CBSE Class 8

On this page, you will find Light Class 8 Notes Science Chapter 16 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 16 Light will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 16 Light

Light Class 8 Notes Understanding the Lesson

1. Light is a form of energy.

2. When light reaches our eyes after striking an object, we are able to see an object.

3. The bouncing back of light into the same medium after it falls on a surface is called reflection.

4. The ray of light striking the surface is called an incident ray.

5. The ray of light which is returned back into the same medium is known as the reflected ray.

7. The perpendicular drawn to the reflecting surface at the point where incident ray strikes the mirror is called normal.

8. The angle between the incident ray and the normal is called the angle of incidence.

9. The angle between the reflected ray and the normal is called the angle, of reflection.

10. Laws of reflection:

• The angle of incidence is equal to the angle of reflection.
• The incident ray, the reflected ray and the normal all lie in the same plane.

11. When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as irregular reflection.

12. The reflection of light from a smooth and polished surface is known as regular reflection.

13. Two mirrors inclined to each other give multiple images.

14. Kaleidoscope is a device based on the principle of multiple reflections.

15. Sunlight is referred to as white light which consists of seven colours.

16. Splitting of white light into its constituent colours is called dispersion.

15. The human eye is an important sense organ that enables us to see the world around us. It is nearly spheri¬cal in shape.

16. Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.

17. Blind spot is a portion on the retina where the nerve fibres enter the optic nerve. The image falling on the portion can’t be seen.

18. A normal eye can see nearby and distant objects clearly.

19. Long-sightedness or hypermetropia is a defect of the eye where the person cannot clearly see the nearby objects while in short-sightedness or myopia, the far-away objects can not be seen clearly. Visually challenged persons can read and write using the Braille system.

20. Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

Class 8 Science Chapter 16 Notes Important Terms

Angle of incidence: The angle between the incident ray and the normal is called the angle of incidence.

Angle of reflection: The angle between the reflected ray and the normal is called the angle of reflection.

felind spot: The portion on the retina where the nerve fibres enter the optic nerve is called blind spot. The image falling on this portion can’t be seen.

Braille: The system of representing characters by raised dots which enables the blind person to read is called Braille.

Cones: Visual receptor cells in retina, which are sensitive to bright light and sense colour are called cones.

Cornea: The transparent front part of the eye is called cornea.

Diffused/Irregular reflection: When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as irregular/diffused reflection.

Dispersion: The splitting of light into its constituent colours is known as dispersion.

Incident ray: The ray of light striking the surface is called as incident ray.

Iris: The dark muscular structure behind the cornea is called iris.

Kaleidoscope: A device based on the principle of multiple reflections is called kaleidoscope.

Lateral inversion: The phenomenon of changing side, i.e, left to right and right to left by the mirror while forming an image is called lateral inversion.

Pupil: The small opening in the cornea is called pupil.

Reflected rays: The rays of light which returns back from the surface after reflection is known as refl ected ray.

Reflection: The bouncing back of light into the same medium after it falls on a surfac is called reflection.

Regular reflection: When all the parallel rays reflected from a smooth and polished surface is also parallel is called regular reflection.

Retina: The site where the image is formed in the eye is called retina.

Rods: The nerve cells on retina which are sensitive to dim light are called rods.

On this page, you will find Some Natural Phenomena Class 8 Notes Science Chapter 15 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 15 Some Natural Phenomena will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 15 Some Natural Phenomena

Some Natural Phenomena Class 8 Notes Understanding the Lesson

1. Lightning is an electric spark on a huge scale. It is caused by the accumulation of charges in the clouds.

2. Some objects can be charged by rubbing with other objects. These objects are called charged objects.

3. There are two types of charges – positive and negative.

4. The charge acquired by a glass rod when it is rubbed with silk is called positive.

5. The charge on an ebonite rod when rubbed with fur, wool or flannel is considered as negative.

6. The electric charges generated by rubbing are called static charges.

7. When charges move they constitute an electric current. Thus, moving charges are called current.

8. Like charges repel each other and unlike charges attract each other.

9. A device used to test whether an object is carrying charge or not is called an electroscope.

10. Electric charge can be transferred from a charged object to another through a metal conductor.

11. The process of transferring of charge from a charged object to the earth is called earthing.

12. When a body loses charges to the earth or any other it is said to be discharged.

13. The process of electric discharge between clouds and the earth or between different clouds causes lightning.

14. Lightning strike could destroy life and property. It is, therefore, necessary to take measures to protect ourselves.

15. During lightning and thunderstorm no open place is safe. A house or a building is a safe place. During travelling by car or by bus, it is safe to stay inside with windows and doors of the vehicle shut. Carrying an umbrella is not at all a good idea during thunderstorm. If in a forest, shelter should be taken under shorter trees.

16. Lightning can strike telephone cords, electrical wires and metal pipes. Electrical appliances like computer, TV, etc., should be unplugged. Electrical lights can remain on.

17. Lightning conductor is a device used to protect buildings from the effect of lightning.

18. 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.

19. Earthquake can cause a great loss to our life and property. It can cause immense damage to buildings, bridges, dams and people. It can also cause floods, landslides and tsunamis.

20. Unfortunately, we are not yet able to predict an earthquake accurately.

21. The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale.

22. Earthquakes having magnitudes higher than 7 on the Richter scale cause a great destruction to our life and property.

23. Earthquakes are caused by the movement of plates, the boundaries of the plates are the weak zones where earthquakes are more likely to occur. The weak zones are known as seismic or fault zones.

24. We should adopt precautionary and protective measures to save ourselves from the upcoming damages of an earthquake.

Class 8 Science Chapter 15 Notes Important Terms

Crust: The uppermost layer of Earth’s surface (8 km – 32 km) is termed as crust.

Discharge: Discharge is the release or transmission of charges from one object to another through a medium like liquid, gas or solid.

Earth’s plates: The outermost layer of the earth is fragmented. Each fragment is called a plate.

Earthquake: An earthquake is a sudden shaking or trembling of the earth which lasts for a very short time. It is caused by deep disturbances caused by movement of earth’s plates inside the earth’s crust.

Electroscope: It is a device used to test whether an object is charged or not.

Lightning: It is the process of electric discharge between cloud and the earth or between different clouds.

Lightning conductor: It is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed on the roof of elevated structure.

Negative charge: The charge of an object due to excess of electrons is called negative charge.

Positive charge: The charge of an object due to loss of electrons is called positive charge.

Richter scale: The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale.

Seismograph: It is an instrument which measures and records the magnitude of an earthquake in terms of the shock waves it produces.

Thunder: The loud noise accompanied by lightning is called thunder.

Thunderstorm: A storm accompanied by thunder and lightning is called thunderstorm.

Transfer of charge: Electric charges can be transferred from a charged object to another through a metal conductor.

Tsunami: A sudden violent change in the earth’s surface resulting from a destructive sea wave caused by an earthquake or volcanic eruption is known as tsunami. Coastal areas around the ocean suffer huge Mosses.

Tremor: A small earthquake is called tremor.

On this page, you will find Sound Class 8 Notes Science Chapter 13 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 13 Sound will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 13 Notes Sound

Sound Class 8 Notes Understanding the Lesson

1. Sound is defined as a form of energy that travels through medium in the form of vibrations.

2. A sound can be produced by:

• beating
• rubbing
• blowing
• plucking

3. The movement that produces sound in rapid to and fro motion is called vibration.

4. Sound requires medium to travel. Sound can travel through solids, liquids and gases but not through vacuum.

5. Sound travel fastest in solid and slowest in gases.

6. In human beings, the sound is produced by the voice box or the larynx.

7. Voice box is located at the upper end of the windpipe.

8. The eardrum senses the vibration of sound and sends the signal to the brain. This process is called hearing.

9. A vibration has three important characteristics – frequency, amplitude and time period.

10. Frequency is defined as the number of vibrations made by a vibrating body in one second. Its unit is hertz (Hz).

11. Amplitude is defined as the maximum extent to which a vibrating body can vibrate.

12. Time period is defined as the time taken by a vibrating body for one complete vibration.

13. Loudness is the characteristic of sound that enables us to distinguish a loud sound from low sound.

14. Pitch is a characteristic of sound that enables us to distinguish a shrill sound from the grave (hoarse) sound.

15. The term quality is defined as the characteristic of sound by virtue of which we can easily differentiate the two sounds of same pitch.

16. The unwanted and unpleasant sound that causes discomfort is called noise.

17. The sound that we enjoy from musical instruments are called musical sound.

18. Presence of excessive or unwanted sounds in the environment is called noise pollution.

19. Plantation on the roadside and elsewhere can reduce noise pollution.

Class 8 Science Chapter 13 Notes Important Terms

Amplitude: is defined as the maximum extent to which a vibrating body can vibrate.

Audible: The type of sounds which we are able to hear are called audible sounds.

Eardrum: Eardrum is a thin membrane through which the sound waves passed.

Hertz: The frequency is expressed in hertz (Hz).

Larynx: Larynx is the organ which produces sound in the human being. It is also called voice box.

Loudness: Is the characteristic of sound that enables us to distinguish a loud sound from low sound.

Noise: The sound which are unpleasant to hear are termed as noise.

Oscillation: The to and fro motion of the vibrating particles about its mean position is called oscillation.

Pitch: The characteristic of sound by which we distinguish between different sounds of the same loudness is known as pitch.

Shrillness: The property of sound that depends upon frequency of vibrating object is known as shrillness.

Time period: The time taken by the bob of the pendulum to complete one oscillation, is called its time period.

Ultrasonic sound: The sound which have frequencies greater than 20,000 Hz is called ultrasonic sound.

Vibration: The movement of a body from one extreme position to the other is termed as vibration.

Voice box: It is that part by which sound is produced in humans.

Windpipe: The pipe which connects the larynx with the lungs is called windpipe.

On this page, you will find Chemical Effects of Electric Current Class 8 Notes Science Chapter 14 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 14 Chemical Effects of Electric Current will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Chapter 14 Notes Chemical Effects of Electric Current

Chemical Effects of Electric Current Class 8 Notes Understanding the Lesson

1. The substances that allow the electric current to pass through them are called conductors; e.g., copper, aluminium, etc.

2. The substances that do not allow the electric current to pass through them are called insulators; e.g., I rubber, plastic, wood, etc.

3. Some liquids are good conductors of electricity and some are poor conductors.

4. Most liquids that conduct electricity are solutions of acids, bases and salts.

5. Pure or distilled water is free of salts and thus act as insulator or a bad conductor of electricity. Water from tap, handpumps, wells, etc., is not pure but a solution. It contains small amount of mineral salts dissolved in it. This water is thus a good conductor of electricity.

6. Common salts when dissolved in distilled water, makes it a good conductor.

7. The passage of an electric current through a conducting solution causes chemical reactions such as formation of bubbles of a gas on the electrodes, deposits of metals on the electrodes, changes of colour of solutions, etc., is known as chemical effects of current.

8. Electroplating is one of the most common application of chemical effects of current. It is the process of depositing a layer of any desired metal on another material by means of electricity.

9. Electroplating is done to make objects shiny in appearance, resistant to scratches and corrosion.

Class 8 Science Chapter 14 Notes Important Terms

Electrode: An electrode is a conductor that allows electric current to pass from one medium to another using the graphite or metal plates or rods.

Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. It is done by using an electrolytic cell.

Good conductor: The materials which allow electric current to pass through them are called good conductors of electricity; e.g., copper, aluminium, etc.

Poor conductor: The materials which do not allow electric current to pass through them are called poor or bad conductors of electricity. They are also known as insulators; e.g., rubber, plastic, wood, etc.

LED: It is an electronic device containing two wires called leads, one lead (longer) is connected to the positive (+) terminal and the other (smaller) to the negative (-) terminal of the battery. It starts emitting light even when a very weak current flows through it. It is actually Light Emitting Diode.

On this page, you will find Friction Class 8 Notes Science Chapter 12 Pdf free download. CBSE NCERT Class 8 Science Notes Chapter 12 Friction will seemingly help them to revise the important concepts in less time.

CBSE Class 8 Science Notes Chapter 12 Friction

Friction Class 8 Notes Understanding the Lesson

1. Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.

2. Friction always acts in a direction opposite to the direction of motion.

3. The force of friction always opposes the applied force. So it is defined as a force that opposes motion.

4. Friction depends upon the nature of surfaces in contact. It also depends upon the weight of the body.

5. Friction is greater in rough surface and smaller in smooth surface.

6. Friction is caused by the interlocking of irregularities between the two surfaces, Friction is independent of the area of contact.

7. Friction is both a friend and a foe. It is a necessary

8. Friction can never be reduced to zero.

9. Friction is also caused due to the force of adhesion.

10. The substances that reduce friction are known as I lubricants. They form a thin layer on the moving I surfaces. So, they do not rub directly against each other.

11. Friction can be reduced by using grease, oil, powder, ball bearings and a cushion of dry air between the 1 moving surfaces.

12. The force required to overcome friction at the instant an object starts moving from rest is a measure of static friction. It comes into play when try to move an object at rest.

13. When one body or object rolls over the surface of another body or object, the resistance to its motion is known as rolling friction.

14. When one object slides over another object, the friction that comes into action is called sliding friction.

15. The force of friction exerted by fluids is also known as drag. The common name of gases and liquids is fluid.

16. Ball bearings are used to reduce friction.

17. Fluid friction of an object depends upon its speed with respect to the fluid, the shape of the object and the nature of the fluid.

18. A special shape is given to overcome drag of an object. For example, shape of an aeroplane and ship are streamlined. Birds and fish have naturally got such shape.

19. Sometimes we deliberately increase friction by using brake pads in the brake system of bicycles and auto¬mobiles and by grooving soles of shoes or tyres of vehicles, etc.

Class 8 Science Chapter 12 Notes Important Terms

Ball bearing: A bearing in which the parts are separated by a ring of small freely rotating metal balls.Ball bearings are used to reduce friction.

Drag: The frictional force exerted by fluids is called drag.

Fluid friction: Friction that occurs in liquids or gases is called fluid friction.

Friction: The resistance that one surface or object encounters when moving over another is known as friction. It opposes the relative motion between two surfaces in contact.

Interlocking: Irregularities in two surface may clasp with each other, resulting in their interlocking.

Lubricants: The substances that reduce friction are called lubricants.

Rolling friction: When one object rolls over another object, the resistance to its motion is called rolling friction.

Sliding friction: When one surface slides over another surface, sliding friction gets into action.

Static friction: To counter balance the applied force on the object, static friction comes into action.