CBSE Class 8

In this page, we are providing Some Natural Phenomena Class 8 Extra Questions and Answers Science Chapter 15 pdf download. NCERT Extra Questions for Class 8 Science Chapter 15 Some Natural Phenomena will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 15 Extra Questions and Answers Some Natural Phenomena

Extra Questions for Class 8 Science Chapter 15 Some Natural Phenomena with Answers Solutions

Some Natural Phenomena Class 8 Extra Questions Very Short Answer Type

Question 1.
What are the two natural calamities?
Answer:

• Lightning and
• Earthquake.

Question 2.
Name other natural calamities except lightning and earthquake.
Answer:
Winds, storms and cyclones.

Question 3.
Name the two types of charges.
Answer:

• Positive; and
• Negative.

Question 4.
Mention the interactions of two types of charges.
Answer:
Like charges repel each other while unlike charges attract each other.

Question 5.
Name the device used to protect buildings from lightning.
Answer:
Lightning conductor.

Question 6.
In which direction does the shock waves produced by an earthquake travel?
Answer:
Both on the surface and inside the earth.

Question 7.
What happens when two clouds with unlike charges approach each other?
Answer:
Lightning strikes

Question 8.
Who discovered the static electricity or lightning in clouds and when?
Answer:
Benjamin Franklin in 1752.

Question 9.
What actually causes lightning?
Answer:
Lightning is caused by the accumulation of charges in the clouds.

Question 10.
What happens when amber is rubbed with fur?
Answer:
It develops the capacity to attract light objects.

Question 11.
What is static electricity?
Answer:
The electrical charge reproduced by rubbing two objects is called static electricity.

Question 12.
What happens when a glass rod and silk cloth are rubbed with each other?
Answer:
The glass rod gets positively charged and silk cloth negatively charged.

Question 13.
What is lightning?
Answer:
Lightning is&an electric spark on huge scale.

Question 14.
What are weak zones called?
Answer:
Seismic or fault zones.

Question 15.
How are most earthquakes caused?
Answer:
Most earthquakes are caused by the movement of earth’s plates.

Question 16.
What is a plate?
Answer:
Each fragment of the outermost layer of the earth is called plate.

Question 17.
What is the uppermost layer of the earth called?
Answer:
Crust

Question 18.
How is an earthquake caused?
Answer:
It is caused by a disturbance deep inside the earth’s crust.

Question 19.
What are seismic waves?
Answer:
Waves produced on the Earth’s surface because of tremors.

Question 20.
When and where a major tsunami took place in India?
Answer:
It occurred in the Indian ocean on 26th December 2004.

Question 21.
What are the natural calamities caused by earthquakes?
Answer:
Earthquakes can cause floods, landslides and tsunamis.

Question 22.
Which kind of material is used to transfer charges from one body to another?
Answer:
Metal conductor

Some Natural Phenomena Class 8 Extra Questions Short Answer Type

Question 1.
What is lightning? What causes lightning?
Answer:
Lightning is also an electric spark, but on a huge scale. It is caused by the accumulation of charges in the clouds.

Question 2.
What is an electric charge? What are charged objects?
Answer:
When a plastic refill is rubbed with polythene it acquires a small electric charge. Similarly when a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects.

Question 3.
What is static charge? How does it differ from electric current? ‘
Answer:
The electric charges generated by rubbing are called static charges. The static charges do not move while charges move in electric current.

Question 4.
What do you mean by electric discharge? How does it occurs?
Answer:
When the negative and positive charges meet, streaks of bright light and sound are produced. This process is called electrical discharge. For example, electric discharge occurring between two or more clouds or between clouds and earth.

Question 5.
What is earthing? What is the application of earthing?
Answer:
The process of transfer of charges from a charged object to the earth is called earthing. It is provided in buildings to protect from electrical shocks due to any leakage of electrical current.

Question 6.
How does electric discharge occur in clouds?
Answer:
At the time of thunder negative charges are accumulated near the clouds and positive charges near the ground. When these charges meet, electric discharge takes place between the ground and clouds. In this process, a large amount of energy is released.

Question 7.
What is lightning conductor? Where is it fixed?
Answer:
Lightning conductor is a device which is used to protect buildings from the danger of lightning. It is fixed at the top of the building.

Question 8.
What is an earthquake? How is it caused?
Answer:
Sudden shaking and trembling of earth is called an earthquake. It is caused mostly due to the movement of earth’s plates inside the crust.

Question 9.
What are fault zones? Name the fault zones in India.
Answer:
Since earthquakes are caused by the movement of plates, the boundaries of the plates are weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones. In India the most threatened areas or fault zones are Kashmir, Western and Central Himalayas, the Indo-Gangetic Plain, Rann of Kutch, etc.

Question 10.
How can tremors be caused?
Tremors on the earth can also be caused when a volcano erupts, or a meteor hits the earth, or an underground nuclear explosion is carried out.

Question 11.
What are seismic waves? How are these waves recorded?
Answer:
The tremors produce waves on the surface of the earth. These are called seismic waves. These waves are recorded by an instrument called the seismograph.

Some Natural Phenomena Class 8 Extra Questions Long Answer Type

Question 1.
What is lightning? How does lightning strike?
Answer:
Lightning is an electric spark, but on a huge scale. It is caused by the accumulation of charges in the clouds. When two clouds carrying opposite charges come very close to each other, the charges flow with great speed from one cloud to another through the air between them. Consequently, a very bright spark is produced.

The spark caused due to the transfer of electric charge between two clouds causes lightning. It can occur when electric charges flow from one part of a cloud to another or from a cloud to the ground. Lightning is accompanied by large amounts of electric charges and very high temperatures. The huge amount of heat produced makes the air expand very suddenly what causes vibration to occur, resulting in a loud sound called thunder.

Question 2.
Explain the process of electric discharge.
Answer:
During the development of a thunderstorm, the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. By a process, the positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower 1 edges. There is accumulation of positive near the ground also.

When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Finally negative and positive charges meet, producing streaks of bright light and sound called lightning and thunderstorm respectively. This process is known as electric discharge. This can occurs between two or more clouds, or between clouds and the earth.

Question 3.
What safety measures should be taken during lightning and thunderstorm?
Answer:
The following safety measures are advisable to be adopted to protect from lightning and thunderstorm:

• No open place is safe. A house or a building is a safe place. If travelling by car or by bus, it is safe to stay inside with windows and doors of the vehicle shut.
• If we are outside, the following things are important to be kept in mind:

(a) Open vehicles, like motorbikes, tractors, construction machinery, fields, tall trees, shelters in parks, elevated places do not protect us from lightning strikes.
(b) Carrying an umbrella is not at all a good idea during thunderstorms.
(c) If no shelter is available and we are in an open field, we should keep away from all trees. We should stay away from poles or other metal objects. We should not lie on the ground. Sitting in a pose as given in the Fig. 15.8 is advisable.

• If we are inside the house, we should take care as advised further: Lightning can strike telephone cords, electrical wires and metal pipes. During a thunderstorm, contact with these should be avoided. It is safer to use mobile phones and cordless phones. However, it is not wise to call up a person with a wired phone. Bathing should be avoided. Electrical appliances should be unplugged.

Question 4.
What is a lightning conductor? How does it work?
Answer:
Lightning conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the buildings during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground as shown in the figure. The rod provides easy route in the transfer of electric charge to the ground. The metal columns used during construction, electrical wires and water pipes in the buildings also protect us to an extent. But we should not touch them during thunderstorm.

Question 5.
What is an earthquake? What causes an earthquake? Explain.
Answer:
An earthquake is a sudden shaking or trembling of the earth. It lasts for a very short time. It is caused by a disturbance deep inside the earth’s crust. We know that tremors are caused by the disturbance deep down inside the uppermost layer of the earth called crust (Fig. 15.10). The outermost layer of the earth is fragmented. Each fragment is called a plate (Fig. 15.11). These plates are in continual motion. When they brush one another, or a plate goes under another due to collision (Fig. 15.12), they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

Question 6.
What are the measures we should adopt to protect against an earthquake?
Answer:
We know that earthquakes cannot be predicted. It is, therefore, important that we should take necessary precautions to protect ourselves all the time as given below:

• In seismic zones it is advisable to make the structure of the buildings simple so that it is ‘Quake Safe’. Modern building technology can make it possible.
• In highly seismic areas, the use of mud or timber is better than using heavy construction materials.
• Since some buildings may catch fire, it is necessary that all buildings, especially tall buildings, have fire fighting equipment in working order.
• If we are at home, we should take shelter under a table and stay there till the shaking stops. We should stay away from tall and heavy objects that may fall on us. If we are in bed, we should protect our head with a pillow.
• If we are at outdoors, we should find a clear spot, away from buildings, trees and overhead power lines and drop to the ground. If travelling in a car or a bus, do not come out and drive slowly to a clear spot.

Some Natural Phenomena Class 8 Extra Questions HOTS

Question 1.
If aluminium strips of an electroscope are replaced by plastic strips and a charged body is brought in contact with the metal clip. What will happen?
Answer:
The plastic strips will show repulsion. Charges from the charge body will be transfer from the metal rod to the plastic strips. As a result, similar charges will develop on the plastic strips and repulsion will occur.

Question 2.
If a charged plastic straw is brought near another uncharged plastic straw, what will happen?
Answer:
They will attract each other due to presence of unlike charges on them.

Question 3.
During construction of a building, the lightning conductor was a little shorter and cannot be buried in the ground. Would the lightning conductor be still effective? Explain.
Answer:
No, it will not be effective. Since lightning conductor was not connected properly to the earth, therefore, the charge will not pass through to the earth.

Question 4.
If air and cloud were good conductors of electricity, do you think lightning could occur? Explain.
Answer:
If air and cloud were good conductors of electricity then charge separation will not take place and hence lightning will not occur.

Question 5.
The strips of an electroscope diverge when a charged body is brought in contact with the metal clip.
What will happen to the strips if we gently touch the metal clip with hands?
Answer:
The strips will collapse due to discharging of the charges through our hand.

Question 6.
On a dry day why do you get a slight shock on touching the screen of a television or computer monitor (with picture tube)?
Answer:
Electric charges accumulated on the screen of television or computer monitor get discharge through our body. Thus, we get a slight shock.

Some Natural Phenomena Class 8 Extra Questions Value Based (VBQs)

Question 1.
Ms Neena, Science teacher of class VIII, taught children how to protect themselves and what to do during an earthquake. She even performed an earthquake drill in school for better understanding in children. Children enjoyed this drill and learned a lot from this.
(a) What to do during an earthquake if you are stuck indoor?
(b) What causes earthquakes?
(c) How you must keep yourself ready for an earthquake?
(d) What values of Ms Neena is shown here?
Answer:
(a) The following must be done if someone had stuck indoor:

• Stay away from glass, windows, outside doors and walls.
• Stay away from anything that could fall such as lightning fixtures or furnitures.
• Get under a sturdy table/desk, hold it firmly and cover your head.
• Stay calm and do not panic. Stay inside until shaking stops and it is safe to go outside.

(b) Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake.

(c) We must keep ourself ready for an earthquake by:

• Having proper knowledge about do’s and don’ts during an earthquake.
• Keeping a disaster kit ready in the time of need.
• Helping needy and injured person after an earthquake.

(d) Ms Neena has future vision, scientific temperament, intelligent, compassionate, caring, dedicated, etc.

In this page, we are providing Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14 pdf download. NCERT Extra Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current with Answers will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 14 Extra Questions and Answers Chemical Effects of Electric Current

Extra Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current with Answers Solutions

Chemical Effects of Electric Current Class 8 Extra Questions Very Short Answer Type

Question 1.
What are good conductors?
Answer:
The substances that conduct electricity through them are called good conductors.

Question 2.
What are insulators or poor conductors?
Answer:
The substances that do not conduct electricity through them are poor conductors or insulators.

Question 3.
Give four examples of conductors.
Answer:
Copper, iron, aluminium and brass.

Question 4.
Give four examples of insulators.
Answer:
Air, wood, rubber and plastic.

Question 5.
Name two metal objects which have a coating of another metal.
Answer:
Handlebars of bicycles, bathroom taps.

Question 6.
What do we get on electrolysis of acidified water?
Answer:
Hydrogen and oxygen gas.

Question 7.
Is air a bad or good conductor?
Answer:
A bad conductor.

Question 8.
Which metal is plated on handle bars of cycles and rim of wheels?
Answer:
Chromium

Question 9.
What is the full form of LED?
Answer:
Light Emitting Diode.

Question 10.
How do we check the electric current?
Answer:
We check the electric current by using a tester.

Question 11.
Which part of an atom is responsible for flow of current?
Answer:
Electron

Question 12.
Why do most liquids conduct electricity?
Answer:
Due to the presence of ions in them, most liquids conduct electricity.

Question 13.
An LED is more efficient device than a bulb. Why?
Answer:
LED is more efficient because it can glow even when a weak or less current flows through it.

Question 14.
Do lemon juice or vinegar conduct electricity?
Answer:
Yes, they conduct electricity.

Question 15.
How is conductivity of liquids tested?
Answer:
By using a tester.

Question 16.
Is water from taps, handpumps, wells and ponds a good conductor?
Answer:
Yes, water from these sources is a good conductor.

Question 17.
What makes distilled water a good conductor?
Answer:
Salts when mixed with distilled water make it a good conductor.

Question 18.
Why is a layer of zinc coated over iron?
Answer:
To prevent iron from corrosion and rust.

Question 19.
Will the solution of sugar in distilled water conduct electricity?
Answer:
No

Question 20.
Why is tin electroplated on iron to make cans used for storing food?
Answer:
Tin is less reactive than iron. Tin coating prevents food from coming in contact with iron and thus pre¬vents it from getting spoiled or corroded.

Question 21.
Why we ifse chromium electroplating on taps and bars of bicycle instead of silver and gold?
Answer:
Silver and gold are very expensive comparatively to chromium.

Question 22.
What type of effect of current do the deposits of metal on electrodes show?
Answer:
Chemical effect

Question 23.
What effect of current does electroplating show?
Answer:
Chemical effect

Question 24.
Which effect of current causes the bulb to glow?
Answer:
Heating effect

Question 25.
Which part of the bulb glows?
Answer:
Filament

Question 26.
Name the three effects of electric current.
Answer:
Heating, magnetic and chemical effect.

Question 27.
How can the magnetic effect of current be checked?
Answer:
By using magnetic compass.

Question 28.
What do we see when the compass needle is brought near a wire in which current is flowing?
Answer:
The needle deflects.

Question 29.
What is electroplating?
Answer:
Deposition of thin layer of a metal over other metal by electrolysis is called electroplating.

Chemical Effects of Electric Current Class 8 Extra Questions Short Answer Type

Question 1.
Define good conductors and poor conductors or insulators.
Answer:
The materials that conduct electricity through them are called good conductors whereas those that do not conduct electricity are called poor conductors or insulators. For example, copper, brass, aluminium, iron, etc., are conductors whereas rubber, plastic, wood, air, etc., are insulators.

Question 2.
How is the conductivity of liquids tested?
Answer:
The free ends of the tester is dipped in the liquid. If the bulb glows, the liquid is said to be a conductor. If not, it is an insulator.

Question 3.
Show with the help of a diagram that lemon juice and vinegar are good conductors of electricity.
Answer:
When the ends of a tester is dipped in lemon juice or vinegar, the bulb glows. This process indicates that lemon juice and vinegar, both, are good conductors of electricity.

Question 4.
What is an LED? Why is it preferred to other type of bulbs?
Answer:
The electric device which is used in the tester instead of bulb is an LED. Its full form is Light Emitting Diode. It is preferred to other bulbs as it can glow even when weak or less current flows through it.

Question 5.
Explain the conductivity of water.
or
Normal water conducts electricity while the pure or distilled water does not. Explain why?
Answer:
Normal water that we get from sources such as taps, handpumps, wells, ponds, etc., is not pure. It may contain several salts dissolved in it naturally. This water is thus good conductor of electricity. The pure or distilled water is free of salts and is a poor conductor.

Question 6.
Give an example of chemical effect of the electric current.
Answer:
The passage of an electric current through a conducting solution causes chemical reactions as a result,
bubbles of a gas are formed, or deposits of metal are seen on electrodes or changes in colour of solution , may occur. These are some of the chemical effects of electric current.

Question 7.
What is electroplating? What are its uses?
Answer:
The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
Electroplating is a very useful process. This is used to make objects appear shiny and resistant to scratches. It prevents corrosion.

Question 8.
What happens when electric current is passed through the copper sulphate solution?
Answer:
When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it.

Question 9.
How does a bulb glow in liquid? Explain.
Answer:
When the liquid between the two ends of a tester allows the electric current to pass through it, then the circuit of the tester becomes complete and the current flows in the circuit of liquid makes the bulb glow. But when the liquid does not allow the electric current to pass through it, then the circuit of the tester is incomplete and the bulb does not glow.

Question 10.
What is the magnetic effect of electricity? Explain.
Answer:
When electric current is passed through a coil or wire, it behaves like a magnet. This is known as mag¬netic effect of current. It depends on amount of current passing through the coil or wire.

Question 11.
Why is magnetic compass needed to test the conduction of electric current?
Answer:
Sometimes, when the current passing through a conductor is so small that filament of the bulb does not get heated up and the bulb does not glow. In this case, we need magnetic compass to test the conduction of current.

Question 12.
What happens when an electric current is passed through a cut potato for a considerable time?
Answer:
When an electric current is passed through a cut potato for a considerable time, greenish blue spot is formed around positive electrode. The chemical effect of the electric current is involved in this process.

Question 13.
Why is chromium used for electroplating? Why the objects have chromium plating are not made of chromium itself?
Answer:
Chromium has a shiny look. It does not get corroded and it resists scratches. Chromium is however expensive and it may not be economical to make the whole object out of it. So the object is made from a cheaper metal and only a coating of chromium is done over it.

Question 14.
Which metals, except chromium, are used for electroplating other metals?
Answer:
Jewellery makers electroplate silver and gold on ornaments of less expensive metals.
Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Hence, food is protected from getting spoilt. Iron used in bridges and automobiles is coated with zinc to protect them from corrosion and formation of rust. •

Question 15.
Current does not flow in a circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain.
Answer:
Air is a poor conductor of electricity if it is dry but in certain cases like during lightning and when air is moist, air may conduct electricity.

Chemical Effects of Electric Current Class 8 Extra Questions Long Answer Type

Question 1.
On what factors thickness of the electroplated items depend?
Answer:
Thickness of electroplated items depend upon:

• The strength of the current passing through the circuit.
• The concentration of the metal ion in the solution.
• The duration of the time the article has been in the solution.

Question 2.
With the help of a suitable diagram, explain electrolytic refining of copper.
Answer:
To purify copper, a thin plate of pure copper and a thick rod of impure copper are used as electrodes in the acidified solution of CuS04. Pure copper is used as cathode and impure copper is used as anode. When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. From impure copper electrode, an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from solution is restored and the process continues. The impurities are left behind at anode.

Question 3.
Does water conduct electricity? Show with the help of an activity.
or
Show the conductivity of water with the help of an activity.
Answer:
Normal or ordinary water is a good conductor of electricity while distilled water is a bad conductor or insulator. Ordinary water may contain small amount of mineral salts dissolved in it naturally; on the other hand, distilled water is free of salts.

The following activity shows this fact:
About 50 mL of distilled water is taken in a clean and dry beaker. When the tester is dipped into the distilled water, the bulb does not glow which shows that distilled water is a bad conductor of electricity. But when a small amount of common salt is dissolved in distilled water and again tested the bulb glows which shows that distilled water when mixed with salts conduct electricity.

Question 4.
What is electroplating? On which effect of the electric current is it based? Why is it done?
Answer:
The process of depositing or coating a layer of any desired metal on the surface of other material by means of electricity is called electroplating. It is one of the most common applications of chemical effects of electric current.
Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects to make them shiny and at¬tractive.

Question 5.
What are the advantages and disadvantages of electroplating?
Answer:
Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of different metal. The advantages and disadvantages of electroplating are:
Advantages:

• It protects the metals from being corroded.
• It prevents the rusting of metals.
• It makes cheap and dull metals shiny and attractive.
• It can make more reactive metals like iron less reactive.
• Chromium coating on metals give lustre to objects.

Disadvantages

• Pollutants from electroplating industries are very harmful. Some chemicals are very lethal for both human and animals.
• It is an expensive process.

Chemical Effects of Electric Current Class 8 Extra Questions HOTS

Question 1.
Why electric fires are extinguished with either using C02 extinguisher or mud but not water?
Answer:
As water is a good conductor of electricity so it can cause electrocution. Hence, water is avoided in ex¬tinguishing electric fires.

Question 2.
Why do you think electroplated jewelleries are in demand?
Answer:
Electroplated jewelleries are in demand because firstly, they are as shiny and attractive as real jewelleries. They are light-weighted and cost effective. Secondly, one feels free to wear it because of the growing problem of snatching and theft.

Question 3.
Do distilled water conduct electricity? What will happen if we add sugar to it and then salt to it? Explain.
Answer:
No, distilled water do not conduct electricity. If we add sugar to distilled water, then also it will not conduct electricity because sugar do not dissociates into ions. But on adding salt, it will conduct electricity because aqueous salt solution is a good conductor of electricity.

Question 4.
Suppose you want to deposit silver on an iron spoon using silver nitrate as electrolyte. Which terminal of the battery you should connect the spoon? What material should the other electrode be made of?
Answer:
Silver ion is positively charge, so the spoon must be connected to negative terminal to deposit silver on it. The other electrode should be made of silver.

Question 5.
Why potato turns green on passing current? Around which terminal greenish patch is observed?
Answer:
Potato turns green due to chemical effect of current. Around positive terminal greenish patch in potato is observed.

Chemical Effects of Electric Current Class 8 Extra Questions Value Based (VBQs)

Question 1.
Yakub made an circuit as shown in the figure. He observed that the bulb did not glow but on bringing a compass needle near it shows deflection.
He was quite confused that if current is flowing through the circuit then why the bulb is not glowing. Meanwhile his friend Sourav arrived and suggested him to add one more cell in the circuit. The bulb, then started glowing.
(a) Define a circuit.
(b) What does the deflection of a compass needle shows?
(c) Why the bulb did not glow in the first case but glow in the second case?
(d) What value of Sourav is shown here?
Answer:
(a) Circuit is a closed path through which an electric current flows.
(b) Deflection of compass needle shows that the current is flowing in the circuit. It is magnetic effect of
current.

(c) The current flowing through the circuit in first case was too low to make the bulb glow but on add-ing a cell in the second case makes the bulb glow.
(d) Sourav is an intelligent, helpful, analytical and with scientific aptitude.

Question 2.
While demonstrating an experiment to show whether the given liquid conduct electricity or not to class VIII students, teacher reminded everybody that one should not conduct experiment with the electric supply from the mains or a generator or an inverter. They should use electric cells for the activity.
(a) Do liquids conduct electricity?
(b) Why we should not use electric source from mains generator or an inverter?
(c) What values do we get from this?
Answer:
(a) Yes, liquids which are solutions of acids, bases and salts conduct electricity. Other liquids such as oil, alcohol, sugar solution and pure water do not conduct electricity.
(b) Current flowing from mains, generator or an inverter is very large. So to avoid the chances of elec-trocution and short-circuit we must use cells for experiments.
(c) We get awareness of not using main electric supply and precaution to be followed while doing experiment.

In this page, we are providing Sound Class 8 Extra Questions and Answers Science Chapter 13 pdf download. NCERT Extra Questions for Class 8 Science Chapter 13 Sound will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 13 Extra Questions and Answers Sound

Extra Questions for Class 8 Science Chapter 13 Sound with Answers Solutions

Sound Class 8 Extra Questions Very Short Answer Type

Question 1.
What does voice box or larynx of human produces?
Answer:
Sound

Question 2.
In which medium sound propagates the maximum?
Answer:
Solid

Question 3.
Name the sound producing organ in human.
Answer:
Larynx

Question 4.
What is vibration?
Answer:
Back and forth motion of an object.

Question 5.
Do all bodies produce sound?
Answer:
No

Question 6.
How is sound produced?
Answer:
By vibrating bodies.

Question 7.
Name a musical instrument which produces sound by blowing air into it.
Answer:
Flute

Question 8.
What is the unit of frequency?
Answer:
Hertz

Question 9.
What do you mean amplitude?
Answer:
Vibrations produced by vibrating body in one second is known as amplitude.

Question 10.
What is the maximum displacement of an oscillating object is called?
Answer:
Amplitude

Question 11.
How does sound help us?
Answer:
Sound help us to communicate.

Question 12.
What is the unit of loudness?
Answer:
Decibel (dB)

Question 13.
What is audible sound?
Answer:
Frequency between 20 Hz to 20,000 Hz is an audible sound.

Question 14.
In which medium sound travels faster?
Answer:
Solid

Sound Class 8 Extra Questions Short Answer Type

Question 1.
A simple pendulum makes 20 oscillations in 40 seconds. What is the time period and frequency of its oscillation?
Answer:

Question 2.
Sonali heard sound of thunderbolt 5 second after she saw flash of lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s)
Answer:
Distance of Sonali from the place of lightning = 330 x 5 = 1650 m

Question 3.
What is frequency?
Answer:
The number of oscillations per second is called frequency. Its unit is hertz.

Question 4.
What do you mean by oscillatory motion?
Answer:
The to and fro motion of an object is called vibration. This motion in both the direction from its mean position is called oscillatory motion.

Question 5.
Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.
Answer:
No, because in space there is no atmosphere and sound needs medium to travel.

Question 6.
What do you mean by time period?
Answer:
The time taken by a vibrating body to complete one oscillation is called the time period.

Question 7.
What are the harms of noise pollution?
Answer:
Lack of sleep, hypertension, anxiety and temporary or even permanent impairment of hearing.

Question 8.
What do you mean by audible sound?
Answer:
The sound which we can hear clearly is known as audible sound. It has a range of frequencies from 20 Hz to 20,000 Hz.

Question 9.
What are infrasonic sounds?
Answer:
Answer:
Sounds which have frequency lower than 20 Hz are called infrasonic sounds.

Question 10.
What is noise pollution?
Answer:
The presence of unwanted and excessive sound in the environment is called noise pollution.

Sound Class 8 Extra Questions Long Answer Type

Question 1.
State the differences between ultrasonic sound and infrasonic sound?

Question 2.
What are the methods to control noise pollution?
Answer:
Following are the methods to control noise pollution:

• The noise pollution can be controlled by reducing the respective sources of noise pollution.
• The blowing of horns and speaker should be strictly avoided near schools and hospitals.
• More and more trees should be planted on the roadside because trees absorb sound.

Question 3.
What is the property of vibration which determines the pitch of the sound?
Answer:
The frequency is the property which determines the shrillness or pitch of a sound. If the frequency of a sound is higher then we say that the sound has lower pitch.

Question 4.
Define frequency.
Answer:
The number of oscillations completed by a vibrating body in one second is called frequency. The unit of frequency is hertz. It is denoted by Hz. If a vibrating body makes 20 oscillations in a second we say that its frequency is 20 Hz. The human voice can produce frequency between 60 Hz and 13,000 Hz. It is interesting that a human ear can hear sound of frequency between 20 Hz to 20,000 Hz.

Question 5.
A string musical instrument was first plucked with a force of smaller magnitude and then with a force of greater magnitude. In which case would the instrument produce a louder sound?
Answer:
The loudness of sound depends upon the amplitude of vibration. The amplitude of string is larger when it is plucked with greater force and hence the sound will be louder in that case.

Question 6.
Differentiate between musical sound and noise.
Answer:

Sound Class 8 Extra Questions HOTS

Question 1.
How is sound produced and how is it transmitted and heard by us?
Answer:
Sound is a form of energy produced and transmitted by a vibrating matter. It travels in form of waves through matter and moves in to and fro direction. When this wave reach eardrum it makes the eardrum to vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain and we are able to hear the sound.

Question 2.
Suppose a bell is ringing in a vacuum. Will you able to hear the sound?
Answer:
We will not be able to hear the sound of vibration because sound cannot travel in vacuum.

Question 3.
What is the function of hair and wax in ear canal?
Answer:
The hair and wax in the ear canal help to keep out foreign debris such as dirt and bugs.

Question 4.
When we speak and hear, does any part of our body vibrate? Name them.
Answer:
Yes. When we speak, vocal cords vibrate to produce sound and when we hear, eardrum vibrate to receive the sound wave.

Question 5.
We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us.
Answer:
If the sound of vibrating body is audible then only we will be able to heard it otherwise we will not be able to hear it.

Question 6.
Why we are able to hear sound of a clock clearer at night than in day?
Answer:
The noise level is quite low at night. Therefore the sound of the clock appears much clearer at night than in the day.

Sound Class 8 Extra Questions Value Based (VBQs)

Question 1.
On Ramesh’s 13th birthday, his father invited all his friends and their relatives. It was a big party with lots of food and DJs. Ramesh didn’t like the loud sound of DJs and asked his father to play it in a low volume so that their neighbours do not get much disturbed and people in the party can also enjoy the music. Ramesh’s father felt good for his wisdom and did as he said.

(a) Do you enjoy loud sound DJs in parties?
(b) Do you think when loud music is played in a party is acceptable to all the people living in , neighbourhood?
(c) How can you control noise pollution at your end?
(d) What value of Ramesh is shown here?
Answer:
(a) Yes/No (according to your choice)
(b) No, it may be not acceptable to all the people living in neighbourhood.
(c) We can control noise pollution at our end by:

• not playing music loudly.
• planting trees around house.
• cushioning gaps in windows and doors.
• using ear plugs at noisy places.
• doing meditation.

(d) Ramesh is wise, mature, knows hazards of noise pollution, concern about others and good-hearted.

In this page, we are providing Friction Class 8 Extra Questions and Answers Science Chapter 12 pdf download. NCERT Extra Questions for Class 8 Science Chapter 12 Friction will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 12 Extra Questions and Answers Friction

Extra Questions for Class 8 Science Chapter 12 Friction with Answers Solutions

Friction Class 8 Extra Questions Very Short Answer Type

Question 1.
What is the force of friction?
Answer:
The force acting on a moving object equal and opposite to the direction of motion is called force of friction.

Question 2.
What is the cause of friction?
Answer:
The irregularities on the two surfaces in contact is the cause of friction.

Question 3.
What is the force responsible for wearing out of bicycles tyres?
Answer:
Frictional force

Question 4.
Is the friction same for all objects?
Answer:
No

Question 5.
Why are wheels of vehicles made circular?
Answer:
Rolling friction is less than sliding friction.

Question 6.
What is the direction of force of friction acting on a moving object?
Answer:
Opposite to the direction of moving objects.

Question 7.
Why do pieces of luggage fit with rollers?
Answer:
To reduce friction and to pull them easily.

Question 8.
Why does a matchstick catch fire when rubbed on the rough surface of the box?
Answer:
Due to friction between the stick and rough surface a matchstick catches fire.

Question 9.
What is the name of special shape given to objects moving in fluids?
Answer:
Streamlined

Question 10.
Give one example where ball bearings are used.
Answer:
Ceiling fan

Question 11.
Does friction depend on the nature of objects?
Answer:
Yes

Question 12.
What is the use of lubricants?
Answer:
They are used to reduce friction.

Question 13.
Which surface does produce more friction smooth or rough surface?
Answer:
Rough surface

Question 14.
Why is fine powder sprinkled on the carrom board?
Answer:
In order to reduce friction powder is sprinkled on carrom board.

Question 15.
Why is it difficult to walk on the wet marble floor?
Answer:
The wet marble floor has less friction. So it is difficult to move on it.

Question 16.
Why does the jar of a mixer become hot when it is run for few minutes?
Answer:
It becomes hot due to friction.

Question 17.
Name the types of friction.
Answer:

• Static friction
• Sliding friction
• Rolling friction
• Fluid friction

Question 18.
Which force helps us to write on the paper or blackboard?
Answer:
Frictional force

Question 19.
What is drag?
Answer:
The frictional force exerted by fluids is called drag.

Question 20.
What are fluids?
Answer:
Commonly gases and liquids are called fluids.

Question 21.
Give some examples having streamlined body.
Answer:
Aeroplanes, birds, ships, etc.

Question 22.
Oil, creams and grease are called lubricants. Why?
Answer:
Because they reduce friction.

Question 23.
How can fluid friction be minimised?
Answer:
By giving suitable shapes to bodies moving in fluids.

Question 24.
When does static friction come into play?
Answer:
When we try to move an object at rest, static friction comes into play.

Question 25.
Can we reduce friction to zero?
Answer:
No

Friction Class 8 Extra Questions Short Answer Type

Question 1.
If we push the book on the table, it stops after sometime. Why?
Answer:
When we push the book on a table, a force is applied on it in the opposite direction of the motion called force of friction. This force opposes the movement and the book stops.

Question 2.
Why are the worn-out tyres discarded?
Answer:
The worn out tyres are discarded because their tread are worn off and limiting their effectiveness of providing required amount of friction.

Question 3.
Why is it easier for the fish to swim in water?
Answer:
Fish can easily swim in water because it has a streamlined body which produces less friction. So it easily cuts through water and moves in it very easily.

Question 4.
Give some examples to show that friction produces heat.
Answer:
The examples are:

• Rubbing of our hands to keep us warm in winter.
• Rubbing of matchsticks on the rough surface to make fire.

Question 5.
Give some examples of smooth and rough surfaces.
Answer:
Smooth surfaces: Surface of the mirror, surface of wet soaps, glazed tiles, surface of an oily pot, etc.
Rough surfaces: Surface of plyboard, unpainted wall, brick, tyres, etc.

Question 6.
What is a spring balance?
Answer:
A spring balance is a device which measures the force acting on an object. It contains a coiled spring. When a force is applied on it, the spring gets stretched. The pointer moves on the scale showing the magnitude of the force.

Question 7.
How does the friction depend on the nature of the surface?
Answer:
Nature of the surface is one of the factors affecting friction. When we move on any surface, we apply a force to overcome the interlocking of the surfaces. Rough surfaces have a larger number of irregularities and greater frictional force.

Question 8.
What are the two factors on which the force of friction depends?
Answer:
These two factors are:

• The nature, i.e., smoothness or roughness of the surfaces in contact.
• How the surfaces in contact pressed together.

Question 9.
When the two surfaces are pressed harder, friction increases. Explain why?
Answer:
The friction is caused by the interlocking of irregularities in the two surfaces. It is obvious that the force of friction will increase if two surfaces are pressed harder. This can be experienced by dragging a mat when nobody is sitting on it and when a person is sitting on it.

Question 10.
What is a measure of static friction?
Answer:
The force required to overcome friction at an instant an object starts moving from rest is a measure of static friction.

Question 11.
What is a measure of sliding friction?
Answer:
The force required to keep the object moving with the same speed is a measure of sliding friction.

Question 12.
Why is it easier to move the box already in motion than to get it started?
or
The sliding friction is slightly smaller than the static friction. Explain why?
Answer:
When the box starts sliding, the contact points on its surface, do not get enough time to lock into the contact points on the floor. So, the sliding friction is slightly smaller than the static friction. Hence, it is somewhat easier to move the box already in motion than to get it started.

Question 13.
Why are the soles of shoes and tyres of vehicles grooved?
Answer:
The soles of shoes and tyres of vehicles like cars, trucks, etc., are grooved to provide better grip on the floor or roads to move safely because grooving increases friction.

Question 14.
We use ball bearings between the hub and axle of ceiling fan and bicycles. Why?
Answer:
The rolling friction is smaller than the sliding friction. In most machines, sliding is replaced by rolling by using ball bearings to reduce friction. This is why ball bearings are used between the hub and axle of ceiling fan and bicycle.

Question 15.
Why are lubricants applied between the moving part of a machine?
Answer:
When lubricants are applied between the moving part of a machine, a thin layer is formed there and moving surfaces do not directly rub against each other. Interlocking of irregularities is avoided to a great extent and the movement becomes smooth.

Question 16.
How brake stop moving bicycles and automobiles?
Answer:
When we press the brake lever, the brake pads arrest the motion of the rim due to friction and the wheel stops moving. This is how brake stops moving bicycles and automobiles.

Question 17.
People often rub their hands in winter. Why?
Answer:
Friction produces heat. When we rub our hands together, the friction arises between them and heat is produced. This makes our hands warm. This is why people often rub their hands in winter.

Question 18.
Which factors affect fluid friction?
Answer:
The speed of the object with respect to the fluid, shape of the object and nature of the fluid affect fluid friction.

Question 19.
In some cases, we deliberately increase friction. Explain why?
Answer:
We need to increase friction in some cases like grooving in the sole of shoes, the treaded tyres of cars, trucks or other vehicles, using brake pads in the brake system of bicycles and automobiles. If we do not do so, we may slip on the floor or roads, vehicles may slip on the roads and they will not stop, our bicycles and automobiles will not stop, etc.

Friction Class 8 Extra Questions Long Answer Type

Question 1.
What are the various types of friction? Explain.
Answer:
There are mainly three types of friction:
(i) Static friction: The friction existing between a stationary object and the surface on which it’s resting is called static friction. This type of friction is more powerful than others. We need a lot of energy to overcome such type of friction.

(ii) Sliding friction: The friction between the two surfaces in contact when one of them just slides , over the other is called sliding friction. It is also known as kinetic friction. It is less than static friction.

(iii) Rolling friction: When one body rolls over the surface of another body, the resistance of its motion is called rolling friction. Rolling friction is less than sliding friction. It is thus the least friction of three types of friction, i.e., Static friction > Sliding friction > Rolling friction.

Question 2.
What are the causes of friction? Explain in detail.
Answer:
Friction is mainly caused by the following factors:
(i) The interlocking of surfaces: The force of friction arises due to interlocking of the irregular projections on the two surfaces. All surfaces have many irregularities. When we attempt to move one object over the other, we have to apply a force to overcome interlocking of the irregularities in their surfaces and friction is produced. The roughness varies from surface to surface due to varying irregularities on the surfaces. So the more is the roughness of the surface, the larger is the number of irregularities and hence the greater will be the friction.

(ii) Force of adhesion: When the two rough surfaces come in contact, it leads to the formation of various contact points. The atoms or molecules present at such points of contact give rise to attractive forces of adhesion that opposes the relative motion of the bodies. Hence, the force of adhesion acting between two surfaces cause friction.

(iii) Deformations: Soft materials will deform when under pressure. This also increase the resistance of motion. For example, when you stand on a sand bed, you sink slightly, which causes resistance when you try to drag your feet along the sand surface. In this case, you must plow through to move, thus creating resistive force.

(iv) Weight of the body: The greater is the weight of the body, the greater will be the force of friction. If we push a heavy box, it will require greater force to move as the force of friction is greater. On the other hand, it is easier to move a lighter box because it produces less friction.

Question 3.
Explain increasing and decreasing friction with suitable examples.
Answer:
In our daily life, in many cases we increase or decrease friction for our own convenience. Some examples are given below:
Increasing friction:

• Soles of our shoes are grooved to provide the shoes better grip on the floor so that we can move safely. Similarly tyres of vehicles are treaded to increase friction to provide better grip.
• We increase friction by using brake pads in the brake system of bicycles and automobiles.
• Gymnasts apply some coarse substance on their hands to increase friction for better grip.
• Kabaddi players rub their hands with soil for a better grip of their opponents.
• Roads are made rough to prevent from slipping.
• Handle of cricket and tennis are made of rough materials to get better grip.

Decreasing friction:
In some situations, however, friction is undesirable and we would want to minimise it.
For example:

• A few drops of oil are poured on the hinges of a door, the door moves smoothly.
• A bicycle and motor mechanic uses grease between the parts of these machines to reduce friction.
• By polishing surfaces, sprinkling powder on carrom board, we reduce friction.
• Wheel and ball bearings are used in machines and vehicles to reduce friction.

Question 4.
What do you mean by fluid friction? How can fluid friction be reduced?
Answer:
The gases and liquids are called fluid. All of them exert force of friction on solid bodies moving in either of them. The force exerted by fluid is called drag. It depends on speed of the object with respect to fluid. It also depends on the shape of the object and the nature of the fluid. is obvious that when objects move through fluids, they have to overcome friction acting on them.

In process they lose energy Efforts are, therefore, made to reduce friction. So, the objects are given special shapes Birds and fishes have to move about in fluide all the time. Their bodies must have evolved to shapes which would make them lose less energy in overcoming friction. Such shapes are called streamlined This is why shapes of aeroplanes, ships and all vehicles are designed to have shapes which minimise fluid friction.

Question 5.
Write advantages and disadvantages of friction.
Answer:
Some points are given below which show that friction is both a friend and a foe:
(a) Friction as friend:

• It allows us to grip and catch any object.
• It helps us to walk comfortably on the floor.
• It helps to minimise the speed or to stop any moving object.
• It helps us to write.

(b) Friction as foe:

• It causes wear and tear in objects.
• It causes damage to the parts of machines and tools which further require money to get them
  repaired.
• It reduces the speed of moving objects, so more force is required.
• It produces hurdles in moving any object freely.

Friction Class 8 Extra Questions HOTS

Question 1.
Will force of friction come into play when a rain drop rolls down a glass window pane?
Answer:
Yes

Question 2.
Will an object experience any force of friction which is falling through a long straight glass having no air in it?
Answer:
No

Question 3.
Cartilage is present in joints of our body, which helps in their smooth movement. 1f cartilage wears off, how would this affect the movement of joints?
Answer:
Wearing off cartilage will make its surface rough and increase the friction. As a result the movement of joints will become difficult which may lead to joint pains.

Question 4.
Why handle of cricket bat or badminton racquet is rough?
Answer:
To have a better grip by increasing friction between handle of the bat and hands.

Question 5.
Two identical metal sheets, A and B, are rubbed with paper and sand paper respectively. Which one of them will shine more?
Answer:
Metal sheet B will shine more because friction between sandpaper and metal sheet is larger than friction between paper and metal sheet. Thus, sandpaper will be able to remove the outer dull layer of metal more effectively than other.

Friction Class 8 Extra Questions Value Based (VBQs)

Question 1.
On Sunday Razak invited everybody to play carrom in his house. While playing, striker was not moving properly from one place to another. Everybody thought it is their bad luck. But Razia. one of the player. quickly got up and sprinkled some talcum powder on the hoard.

(a) Why Razia sprinkled some talcum powder?
(b) Can you give sumo other example which serves the same purpose!
(c)What value of’ Razia is shown here?
Answer:
(a) Reala sprinkled some talcum powder to make the surface of carrom board smooth and hence reduce friction.
(b) Friction can be reduced by using lubricants, hail bearings and painting the rough surface.
(c) Razia is an intelligent girl with scientific aptitude.

Question 2.
Rani and Shyam while returning from school saw labour pushing hard to move a heavy box B. immediately ran to him and started helping hint in pushing the box whereas Shyam brought two in bars and asked the labour to put them below the box and then to push the box.

(a) I What are the factors that affect friction?
(b) I Who will help the labour more Ram or Shyaxn? How?
(c) What values of Raw and Shyam are shown here?
Answer:
(a) Nature of surfaces in contact. weight of the object. the force of adhesion and deformati0n
(b) Shlain’s suggestion of keeping iron bar below the box will help the labour store Putting the iron bar below the box will make it to roll over the bar. As rolling friction is less than building
will help in moving the box with much easier.
(c) Ram and Sham are helping in nature. Shyam is intelligent with çientific aptitude.

In this page, we are providing Force and Pressure Class 8 Extra Questions and Answers Science Chapter 11 pdf download. NCERT Extra Questions for Class 8 Science Chapter 11 Force and Pressure with Answers will help to score more marks in your CBSE Board Exams.

Class 8 Science Chapter 11 Extra Questions and Answers Force and Pressure

Extra Questions for Class 8 Science Chapter 11 Force and Pressure with Answers Solutions

Force and Pressure Class 8 Extra Questions Very Short Answer Type

Question 1.
What is the name of the instrument used to measure atmospheric pressure?
Answer:
Barometer

Question 2.
Give two examples of contact force.
Answer:

• Muscular force
• Force of friction

Question 3.
Name the force exerted on a ball of dough to make a flat chapati.
Answer:
Muscular force

Question 4.
What kind of force is an electrostatic force?
Answer:
Non-contact force

Question 5.
Is the gravity a property of earth only?
Answer:
No

Question 6.
Name the force due to which every object falls on earth.
Answer:
Gravitational force

Question 7.
What do you mean by pressure?
Answer:
Force per unit area (Force/Area)

Question 8.
Do liquids and gases also exert pressure?
Answer:
Yes

Question 9.
What are the two states of motion?
Answer:

• The state of rest.
• The state of motion.

Question 10.
What kind of force is friction?
Answer:
Contact force

Question 11.
What type of force is gravitational force?
Answer:
Non-contact force

Question 12.
Is it true that force acting on an object can also change its shape?
Answer:
Yes, it is true.

Question 13.
While sieving grains, small pieces fall down. Which force pulls them down?
Answer:
Gravitational force

Question 14.
How can we change the speed and the direction of a moving body?
Answer:
By applying force.

Question 15.
What is the distance moved by an object in unit time called?
Answer:
Speed

Question 16.
Does force of gravity act on dust particles?
Answer:
Yes

Question 17.
Does the force of gravitation exist between two astronauts in space?
Answer:
Yes

Question 18.
What is a force?
Answer:
A push or pull on an object is called force.

Question 19.
What is the SI unit of pressure?
Answer:
Pascal (Pa)

Question 20.
At least how many objects are needed to apply a force?
Answer:
At least two objects are needed to apply a force.

Question 21.
Give one example of gravitational force.
Answer:
An apple falling from the tree to ground.

Question 22.
What is meant by atmospheric pressure?
Answer:
The weight of air acting per unit area is known as atmospheric pressure.

Question 23.
What do you mean by magnitude?
Answer:
The strength of a force is usually expressed by its magnitude.

Question 24.
What is muscular force?
Answer:
The force resulting due to the action of muscles is known as muscular force.

Question 25.
What is contact force?
Answer:
Force that can be applied only when it is in contact with an object is called contact force.

Question 26.
What do you mean by the term atmosphere?
Answer:
The envelope of air all around us is known as atmosphere.

Force and Pressure Class 8 Extra Questions Short Answer Type

Question 1.
Define pressure.
Answer:
The force acting per unit surface area is called pressure. SI unit of pressure is measured in Newton/ Metre2, which is equal to 1 Pascal (Pa).

Question 2.
How do fluids exert pressure?
Answer:
Fluids exert pressure in all directions. Fluids also exert pressure on the walls of the container that hold them.

Question 3.
A force of 100 N is applied on an area of 4 m². Compute pressure being applied on the area.
Answer:
Given: Force = 100 N, Area = 4 m²

Question 4.
Which force is responsible for downward movement of a parachutes? Will he come down with the same speed without the parachute?
Answer:
Force of gravity is responsible for this downward movement. No, without parachute he will come down with a higher speed.

Question 5.
Two thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.
Answer:
Electrostatic force is responsible for this phenomenon. The two balls have similar charges, that’s why they move away due to repulsion between them.

Question 6.
How does an applied force changes the speed of an object?
Answer:
If the applied force is in the direction of motion, the speed of the object increases. But if the force applied in the direction opposite to the motion, then it decreases the speed of the object.

Question 7.
Name the forces acting on the car sticking to an electromagnet in a Junkyard. Which one of them is larger?
Answer:
Magnetic force (in the upward direction) and force of gravity or the weight of the car (downward). Magnetic force is larger than the force of gravity.

Question 8.
What is the similarity between electrostatic and magnetic forces?
Answer:

• Both are non-contact forces.
• Both are attractive as well as repulsive forces.

Question 9.
What are the effects of force on an object?
Answer:

• Force can change the state of motion of an object.
• Force changes the speed of a moving object.
• Force can cause an object to turn or change direction.
• Force can change the shape of an object.

Force and Pressure Class 8 Extra Questions Long Answer Type

Question 1.
What is force? State the difference between contact force and non-contact force. A push or pull on an object is called a force.
Answer:

Question 2.
Define the different types of forces.
Answer:
Force can act on a body from a distance or by being in contact with it. Depending on this, forces can be classified as contact and non-contact forces.
(a) Contact forces: When force is applied on an object by direct or indirect physical contact the applied force is called contact force. Muscular and frictional force are example of contact force.

• Muscular force: The force resulting due to the action of muscles is known as the muscular force.
• Frictional force: The force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

(b) Non-contact forces: When a force is applied to an object by another body that is not in direct contact with it is called non-contact force. Gravitational, magnetic and electrostatic force are example of non-contact force.

• Gravitational force: The attractive force of the earth which acts upon all the objects is known as the force of gravity or just gravity.
• Electrostatic force: The force exerted by a charged body on another charged or uncharged 1 body is known as electrostatic force.
• Magnetic force: The force exerted between a magnet and other magnet or magnetic material is known as magnetic force.

Question 3.
Why it is easier to walk on soft sand if we have flat shoes rather than shoes with sharp heels (or pencil heels)?
Answer:
A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this the ‘flat’ shoes do not sink much in soft sand and it is easy to walk on it. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts a greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on it.

Question 4.
What is pressure? What is the relation of pressure with area on which it is applied?
Answer:
Force exerted on per unit area is called pressure. Pressure is related with area on which it is applied. When the area is increased the pressure exerted is less. But when the area on which pressure is exerted is decrease the pressure increases. So we can conclude that pressure increases with decrease in area.
List the characteristics of pressure exerted by a liquid.

• Liquid exerts pressure in all directions.
• Pressure in liquid does not depends on shape, size and surface area of the container.
• Pressure increases with depth.
• All points at the same level in a liquid are at the same pressure.
• Pressure does not depend on the surface of the immersed object.

Force and Pressure Class 8 Extra Questions HOTS

Question 1.
We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect why?
Answer:
The pressure of air inside our body is same as that of the atmosphere. Therefore, we do not experience its effect

Question 2.
Why do sea divers wear specially designed suits?
Answer:
Since the pressure of liquid increases with the increasing depth of sea. Specially designed suits protect scuba divers from the huge pressure of the water underneath.Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction.

Question 3.
What do you infer about the magnitudes and direction of the forces applied?
Answer:
Both the persons are applying forces from opposite direction with equal magnitudes.

Question 4.
An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down.
Answer:
The initial force is muscular force which sets the arrow in motion. The force of gravity that acts on the arrow in the downward direction brings it to the ground.

Question 5.
Two rods: A and B, having same weight and equal length have different thickness. Rod A is thinner while Rod B is thicker. They are held vertically on the surface of sand. Which one of them will sink more? Why?
Answer:
Rod A will go deeper as it has a smaller area of contact, therefore the same force produces more pres¬sure. In case of rod B the same force produces less pressure.

Question 6.
It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.
Answer:
Blunt blades have larger area compared to the sharp-edged blades. Thus, the applied force produces a lower pressure in case of blunt blades, which makes it difficult to cut the cloth.

Question 7.
Observe the figures given below carefully.

Volume of water in each vessel is shown above. Arrange them in order of decreasing pressure at the base of each vessel. Explain the reason.
Answer:
Pressure of a liquid column depends upon the height of the liquid column and not on volume of the liquid. Decreasing order of pressure at the base of each vessel is B>D>A>C.

Force and Pressure Class 8 Extra Questions Value Based (VBQs)

Question 1.
On Lokesh’s birthday Shreya was given charge to amuse children with some little tricks. Shreya sticked balloons to the wall by just rubbing them in her clothes. She bent the water stream from a tap without touching it. She did so by bringing big balloon near to the flowing water. All children were very happy on seeing this little magic. Everybody praised Shreya.

(a) How do balloons stick to walls?
(b) How Shreya bent the water stream by bringing a big balloon near it and without touching it?
(c) What values of Shreya is shown here?
Answer:
(a) On rubbing the balloon with hair or clothes, it acquire negative charges. The negative charges are attracted to the positive charges on the wall and balloon sticks to the wall.
(b) Negative charge on the balloon attracts positive charge on water molecules. Thus, bent the water molecules.
(c) Shreya is dutiful, friendly with scientific aptitude.