CBSE Class 7

In this page, we are providing Winds, Storms and Cyclones Class 7 Extra Questions and Answers Science Chapter 8 pdf download. NCERT Extra Questions for Class 7 Science Chapter 8 Winds, Storms and Cyclones with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 8 Extra Questions and Answers Winds, Storms and Cyclones

Extra Questions for Class 7 Science Chapter 8 Winds, Storms and Cyclones with Answers Solutions

Winds, Storms and Cyclones Class 7 Extra Questions Very Short Answer Type

Question 1.
What is called the wind?
Answer:
The moving air is called the wind.

Question 2.
What was the speed of wind of cyclone hit in Odisha on 18 October 1999?
Answer:
200 km/hr

Question 3.
What is called the eye of the storm?
Answer:
The centre of a cyclone.

Question 4.
From which wind is the word monsoon derived?
Answer:
The Arabic word ‘mausam’.

Question 5.
What does the word ‘mausam’ mean?
Answer:
Season

Question 6.
What do the wind, from the oceans carry?
Answer:
Water

Question 7.
What bring rain?
Answer:
The winds from the oceans carry water and brings rain.

Question 8.
What are monsoon winds?
Answer:
The winds from the oceans carry water and bring rain. These winds are called monsoon winds.

Question 9.
What is natural disaster?
Answer:
Natural disaster are extreme, sudden events caused by environmental factors that injure people and damage property.

Question 10.
Name two natural disasters.
Answer:
Thunderstorms and cyclones.

Question 11.
Why does the can with hot water get distorted?
Answer:
Due to air pressure.

Question 12.
What is the direction of winds in summer?
Answer:
From the ocean towards the land

Question 13.
What is the direction of winds in winter?
Answer:
From the land to the ocean.

Question 14.
In what type of climate do thunderstorms develop?
Answer:
Hot, humid tropical areas.

Question 15.
Define pressure.
Answer:
The force applied per unit area is called pressure.

Question 16.
Which instrument is used to measure the air pressure at any place?
Answer:
Barometer

Question 17.
Which instrument does measure the wind speed?
Answer:
Anemometer

Question 18.
In which direction does the warm air rise?
Answer:
The warm air rises up.

Question 19.
Name two devices that forecast a cyclone.
Answer:

• Satellites
• Radars

Question 20.
Which instrument is used to measure the direction of the wind?
Answer:
Wind vane

Winds, Storms and Cyclones Class 7 Extra Questions Short Answer Type

Question 1.
Describe the two cyclones that hit Odisha in 1999.
Answer:
Odisha was hit by two cyclones, first on 18 October 1999. The wind speed of this cyclone was 200 km/h. It smashed 45000 houses making 7,00,000 people homeless. On 29 October 1999, another cyclone with wind speed of 260 km/h hit Odisha the second time.

It was accompanied by water waves about 9 m high. It was very destructive. Thousands of people lost their lives. Property worth crores of rupees was destroyed. The cyclone affected agriculture, transport, communication and electricity supply.

Question 2.
When we pour cold water over the can half-filled with hot water, the can slowly gets crumpled, why?
or
Show with the help of an activity that air exerts pressure.
Answer:
Take a tin can. Fill it half with water. Boil the water. After the water gets boiled, remove the can from the flame and immediately close the mouth of the can tightly. Place it in a sink and pour cold water over it. The tin can slowly gets crumpled.

This is due to the fact that when we cover the can and pour water over it, the steam condenses to form water reducing the amount of air inside. The air pressure outside the can is more than that inside the can. That is why the can gets distorted. This shows that the air exerts pressure.

Question 3.
Why does the warm air move upwards?
or
The warm air is lighter than the cold air. Explain.
Answer:
When the air is heated, it expands and occupies large space. When the same thing occupies more space, it becomes lighter. The warm air is, thus, lighter than the cold air and rises upwards.

Question 4.
What causes the winds to flow from the oceans towards the land?
Answer:
In summer, near the equator the land warms up faster and most of the time the temperature of the land is higher than that of water in the oceAnswer:The air over the land gets heated and rises. This causes the winds to flow from the oceans towards the land.

Question 5.
What is thunderstorm?
Answer:
The rising temperatures produce strong upward rising winds. These winds carry water droplets upwards, where they freeze, and fall down again. The swift movement of the falling water droplets along with the rising air create lightning and sound. It is this event that is called thunderstorm. It develops in hot, humid tropical areas like India very frequently.

Question 6.
What is a tornado? Describe.
Answer:
A tornado is a dark funnel-shaped cloud that reaches from the sky to the ground. Its diameter can be as small as a metre or even wider. The funnel of a tornado sucks dust, debris and everything near it at the base and throws them out near the top. Most of the tornadoes are weak. A violent tornado can travel at speed of about 300 km/h. Tornadoes may form within cyclones. In our country they are not very frequent.

Question 7.
What happens when high speed wind blow over the roofs of high buildings and why?
Answer:
When high speed wind blows over the roofs, a low pressure area is created above the roof. However, air pressure below the roof is high. This exerts a pressure on the roof and if the roofs are not firmly fixed, they could be lifted and blown away.

Winds, Storms and Cyclones Class 7 Extra Questions Long Answer Type

Question 1.
Explain with the help of an activity that air expands on heating and contracts on cooling.
Answer:
See the ‘NCERT Intext Activity 8.5’.

Question 2.
Give an activity to show that warm air is lighter than cold air.
Answer:
See the ‘NCERT Intext Activity 8.6’.

Question 3.
Explain how are wind currents generated due to uneven heating between the equator and the poles.
Answer:
The areas close to the equator get maximum heat from the sun. As a result, the air in these regions gets warm. The warm air moves upwards and the cooler air from the regions in the 0-30° latitudes belt on either side of the equator moves in.

These winds blow from the north and south towards the equator. At the poles the air is colder than that at latitudes about 60 degrees. The warm air at these latitudes rises up and cold wind from the polar regions rushes in, to take its place. In this way, wind circulation is set up between these poles and the warmer latitudes as shown below (Fig. 8.10).

Question 4.
How do cyclones cause destruction?
Answer:
Cyclones cause destruction to our life and property. The water waves produced by the wind are so powerful that a person cannot overcome them. The rising water may be as high as 3-12 metres. It moves towards the shore. As a result, the sea-water enters the low-lying coastal areas, causing severe loss of life and property.

It also reduces the fertility of the soil. High-speed winds accompanying a cyclone can damage houses, telephones and other communication systems, trees, etc., causing tremendous loss of life and property. Continuous rainfall may further worsen the flood situation.

Question 5.
Explain the formation of a cyclone.
Answer:
The formation of a cyclone is a very complex process (Fig. 8.11). Before formation of the cloud, water takes up heat from the atmosphere to change into vapour. When water vapour changes back to liquid form as raindrops, this heat is released to the atmosphere. This warms the air around. The air tends to rise and causes a drop in pressure.

More air moves to the centre of the storm. This process is repeated. The chain of events ends with the formation of a very low-pressure system with very high-speed winds revolving around it. It is this weather condition that we call a cyclone. Various factors like wind speed, wind direction, temperature and humidity contribute to the development of a cyclone.

Question 6.
What are the precautions we must take if a storm is accompanied by lightning?
Answer:
We must take following precautions if a storm is accompanied by lightning:

1. We should never take shelter under an isolated tree. If we are in a forest, we should take shelter under a small tree. We should never lie on the ground.
2. We should not take shelter under an umbrella with a metallic rod.
3. We should not sit near a window. Open garages, storage sheds, metal sheds are not safer places to take shelter. A car or a bus is a safe place for shelter.
4. If in water, we should get out of water and go inside a building.

Question 7.
What are the effective safety measures to be adopted in case of a cyclone?
Answer:
Steps should be taken both on the government part and on the part of the people as safety measures to save from cyclonic dangers.
(a) On the part of the government:

• A cyclone forecast and warning service.
• Rapid communication of warnings to the Government agencies, the ports, fishermen, ships and to the general public.
• Construction of cyclone shelters in the cyclone-prone areas, and administrative arrangements for shifting people fast to safer places.

(b) Measures to be taken on the part of the public:

1. People should follow the warnings issued by the Government agencies like meteorological department through TV, radio, or newspapers, etc.
2. People should make suitable arrangements to shift the essential household goods, domestic animals and vehicles, etc., to safer places.
3. People should avoid driving on roads through standing water, as floods may have damaged the roads, and keep ready the phone numbers of all emergency services like police, fire brigade and medical centres.

Some other precautions should be taken, if staying in a cyclone hit area as:

1. Avoid drinking contaminated water. People should take water stored for emergencies.
2. People should keep themselves away from wet switches and fallen power lines.
3. People should not unnecessarily go out.
4. People should cooperate and help their neighbours and other people who need any help.

Winds, Storms and Cyclones Class 7 Extra Questions HOTS

Question 1.
Paheli kept an empty bottle made of plastic inside a refrigerator. After few hours, when she opened the refrigerator she found the bottle had collapsed. Explain the possible reason.
Answer:
The air inside the bottle contracts due to low temperature. Hence pressure inside the bottle becomes less than the outside and the bottle collapsed.

Question 2.
Why an umbrella held upright, at times, gets upturned when high speed wind blows?
Answer:
High speed wind passing over the umbrella creates a low pressure. Thus, the umbrella upturns.

Question 3.
Why is it advisable not to shut all the doors and windows during a storm?
Answer:
Low pressure created by storm may blow away the roof. To avoid this condition, it is not advisable to shut all the doors and windows during a storm.

Question 4.
A house near coastal area has a flag on its roof. Towards which direction the flag will be blown in the afternoon? Explain.
Answer:
The flag will be blown towards the land in the afternoon. This is because land get heated up faster comparatively to the water in sea. So air flows from sea to land.

Question 5.
During lightning and thunderstorm, one should not take shelter under a tree or lie on the ground. Why?
Answer:
Tree may be the tallest object around, making it perfect target of lightning and one of the worst place to seek shelter. If we lie down, an electrical current passing through the ground from a nearby lightning strike can pass right through our body. So the above two positions may prove fatal in case lightning strike.

Question 6.
Suggest some precautions to be taken to prevent the roof of a tin sheet from flying away during a fierce wind storm.
Answer:

• Roof should be perfectly nailed with the house.
• Heavy objects should be kept on the roof.

Winds, Storms and Cyclones Class 7 Extra Questions Value Based (VBQs)

Question 1.
Ramaya while going to school found his bicycle’s tyres to be little deflated. He went to a cycle repairing shop and overfilled his bicycle tube. On seeing this, the shopkeeper adviced him that this is not good for his cycle tube. But Ramaya overlooked shopkeeper’s advice and went to his school. He kept his cycle in the cycle stand.
In afternoon when he came to take his cycle, he observed that its tyre has bursted. He got puzzled why his tyres bursted though they were new.
(a) What is air pressure?
(b) What will happen if we use our bicycle with deflated tyres?
(c) Ramaya went to his school with overfilled tyre tubes but nothing happened to his tyres then. Why did it burst when he was not riding and just kept it in cycle stand?
(d) What value of Ramaya is shown here?

Answer:
(a) Air pressure is the force exerted onto a surface by the weight of the air.
(b) Deflated tyres make moving the bicycle harder and also wear and tear of the tyres soon.
(c) The temperature is maximum in afternoon and the heat of the sun warm the air inside the tube, thus rising its pressure to such an extent which caused the tyre to burst.
(d) Ramaya is inexperienced, he overheard the advice of shopkeeper so he is disobedient also. He lacks scientific knowledge on expansion of air.

Question 2.
Saket and Ali, two friends, built a house for themselves. To expel hot air out of kitchen Saket fitted an exhaust fan on the window of his kitchen and Ali fitted a similar exhaust fan on the wall near the ceiling of his kitchen.
(a)Which of the exhaust fan will expel the hot air more effectively? Why?
(b)How a ventilator works in circulating fresh air in the room?
(c)What values of Saket and Ali are shown here?

Answer:
(a) Exhaust fan fitted by Ali will expel the hot air more effectively because hot air has tendency to move up.
(b) The hot and stale air being lighter rises up and get exhausted through the ventilators. The fresh and cold air being heavier than warm air takes its place. So by this way ventilators helps in circulating fresh air within a house.
(c) Saket is impractical whereas Ali is intelligent and practical in placing the exhaust fan at right place.

In this page, we are providing Weather, Climate and Adaptations of Animals to Climate Class 7 Extra Questions and Answers Science Chapter 7 pdf download. NCERT Extra Questions for Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals to Climate with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 7 Extra Questions and Answers Weather, Climate and Adaptations of Animals to Climate

Extra Questions for Class 7 Science Chapter 7 Weather, Climate and Adaptations of Animals to Climate with Answers Solutions

Weather, Climate and Adaptations of Animals to Climate Class 7 Extra Questions Very Short Answer Type

Question 1.
Why desert animals live in burrows?
Answer:
To escape hot and dry weather they live in burrows.

Question 2.
Name some animals found in polar regions.
Answer:
Penguins, polar bears, foxes and walrus.

Question 3.
The weather pattern of nearly how many years is called the climate of the place?
Answer:
25 years

Question 4.
Name some countries which belong to polar regions.
Answer:
Canada, Greenland, Sweden, Norway, etc.

Question 5.
Name the two regions of the earth having extreme climatic conditions.
Answer:
(i) Tropical region
(ii) Polar region

Question 6.
Name the major types of animals living in the rainforests.
Answer:
Monkeys, apes, gorillas, lions, etc.

Question 7.
Name an instrument used to measure rainfall.
Answer:
Rain gauge

Question 8.
What is weather?
Answer:
The day-to-day condition of the atmosphere at a place is called weather.

Question 9.
When does the minimum temperature of the day occur?
Answer:
In the early morning.

Question 10.
What does the daily weather report predict?
Answer:
The weather for the day.

Question 11.
Which department does prepare the weather reports?
Answer:
The Meteorological Department of the Government.

Question 12.
Who record the weather everyday?
Answer:
Meteorologists

Question 13.
What are the sources of getting daily weather reports?
Answer:
Television, radio and newspapers.

Weather, Climate and Adaptations of Animals to Climate Class 7 Extra Questions Short Answer Type

Question 1.
What is climate?
Answer:
The average weather pattern taken over a long time, say 25 years is called climate of the place. If we find that the temperature at a place is high most of the time, then we say that the climate of that place is hot.

Question 2.
How does the sun cause the change in the weather?
Answer:
The sun is a sphere of hot gases which is burning at a very high temperature. Shape of Earth is round and not flat so the sun’s ray don’t fall evenly on the land and oceAnswer:These differences in temperature create wind and water movement and play important role in determining the weather at any place.

Question 3.
What do you mean by the term adaptation?
Answer:
The modifications of the features and the functions of the body of plants and animals according to the climatic condition of a place where they are living is called adaptation.

Question 4.
Describe the climate of polar regions.
Answer:
The polar regions are covered with snow and it is very cold for most parts of the year. The sun does not set for six months and does not rise for six months. In winters, the temperature can be as low as -37°C. These regions are dominated by Earth’s polar ice caps.

Question 5.
How is the mean temperature for a given month calculated?
Answer:
The mean temperature for a given month is found in two steps. First we find the average of the temperatures recorded during the month. Second, we calculate the average of such average temperatures over many years. That gives the mean temperature.

Question 6.
What is a rain gauge?
Answer:
Rain gauge is an instrument to measure rainfall. It is basically a measuring cylinder with a funnel on top to collect rainwater.

Question 7.
What informations does the daily weather report give?
Answer:
The daily weather report gives information about the temperature, humidity and rainfall during the past 24 hours.

Question 8.
Why do we feel so miserable in the summer afternoon and comparatively comfortable early in the morning?
Answer:
The maximum temperature of the day occurs generally in the afternoon while the minimum temperature occurs generally in the early morning. We, therefore, feel so miserable in the summer afternoon and comparatively comfortable early in the morning.

Question 9.
Describe the climatic condition of the western region of India with the example of that of Rajasthan.
Answer:
The climatic condition of the western part of India, for example Rajasthan shows that the temperature is high during most part of the year. But during winter, which lasts only for a few months, the temperature is quite low. This region, receives very little rainfall. This is the typical desert climate. It is hot and dry.

Weather, Climate and Adaptations of Animals to Climate Class 7 Extra Questions Long Answer Type

Question 1.
Answer:

Question 2.
Explain the adaptations of polar bears to live in polar regions. Give the flow chart also.
Answer:
The adaptations that make the polar bears suitable to live in polar region are:

1. The long curved and sharp claws help polar bear to walk on ice.
2. They also have a layer of fat under their skin. In fact, they are so well insulated that they have to move slowly and rest, often to avoid getting overheated.
3. Polar bears have white fur on their body so that they are not easily visible in the snowy background.
4. The two thick-layers of furs on the body of polar bear protects them from extreme cold.
5. They have a strong sense of smell so that it can catch its prey for food.
   The flow chart below clearly explain the adaptations of polar bears.

Question 3.
How are penguins adapted for cold climate?
Answer:
Following are the characteristics that make them suitable to live in cold climate.

1. Penguins have a thick skin and lot of fat under them to protect them from cold.
2. Their bodies are streamlined and their feet have webs, making them good swimmers (Fig. 7.2)
3. Penguin have thick skin and a lot of fat to protect it from cold. It has white coat that merges well with the white background.
4. They often huddled together to remain warm. (Fig. 7.3)

Question 4.
Write a short note on migration.
Answer:
Migration is physical movement of birds or animals from one area to another for food, space, breeding, escaping harsh condition, etc. Migration is commonly seen in birds living in extreme cold climate to long distances for warmer places during the winter season.

Siberian crane and Arctic tern are some of the migratory birds. Mammals, many types of fish and insects are also known to migrate seasonally in search of more hospitable climates.

Question 5.
Explain the climate of tropical regions.
Answer:
The tropical region has generally a hot climate because of its location around the equator. Even in the coldest month, the temperature is generally higher than about 15°C. During hot summers, the temperature may cross 40°C. Days and nights are almost equal in length throughout the year.

These region get plenty of rainfall. An important feature of the tropical region is the tropical rainforests. Tropical rainforests are found in Western Ghats and Assam in India, Southeast Asia, Central America and Central Africa.

Due to continuous warmth and rain, this region supports variety of animals and plants. For example, monkeys, apes, gorillas, tigers, elephants, leopards, lizards, snakes, birds, insects, etc. Many animals are adapted to living on the trees. Red-eyed frog has developed sticky pads on its feet to help it climb trees on which it lives.

To help them live on the trees, monkeys have long tails for grasping branches. Thus, many other animals have adapted to live in the tropical rainforests in tropical regions because of their characteristics like living on the trees, development of strong tails, long and large beaks, bright colours, sharp patterns, loud voice, diet of fruits, sensitive hearing, sharp eyesight, thick skin, ability to camouflage in order to protect themselves from predators, etc.

Weather, Climate and Adaptations of Animals to Climate Class 7 Extra Questions HOTS

Question 1.
Give one example of an animal that can live both in water and on land.
Answer:
Frog.

Question 2.
Write two common adaptive features of a polar bear which help in keeping it warm./
Answer:

• Thick layer of fat under its skin which insulates its body from cold and keeps it warm.
• Two thick layers of fur which keeps it warm.

Question 3.
What is huddling? How it keeps penguin warm in extreme cold climate?
Answer:
Huddling means to come together closely. When it is very cold, penguins huddle together in groups. Warm air gets trapped between the feathers and they get shielded from the full force of the cold wind outside. The penguins standing at the outside of the group continuously shuffle themselves inside to keep them warm. Thus, all penguins remain warm from extreme cold climate.

Question 4.
Mention two adaptive features in penguin which help it in swimming.
Answer:
Penguin have streamlined body and webbed feet which help it in swimming.

Question 5.
Why is it difficult to predict the weather of a place while it is easy to predict its climate?
Answer:
Climate is the average weather pattern taken over a long time, of a place so it is easy to predict. Weather is a complex phenomenon which can vary over a short period of time and thus is difficult to predict.

Weather, Climate and Adaptations of Animals to Climate Class 7 Extra Questions Value Based (VBQs)

Question 1.
A private zoo in tropical region thought of housing penguins to attract more tourists to its place. They arrange an artificial condition to keep them.
(a) Do you think penguins will be able to survive? Why?
(b) What is the difference between the two habitats, i.e., where penguins live and where they will be shifted?
(c) What kind of artificial conditions will be needed to house penguins in tropical region?
(d) Do you agree with the steps taken by the zoo?
(e) What value of private zoo is shown here?

Answer:
(a) No, because they are adaptive to extreme cold climate.
(b) Temperature is the main difference between the two habitat.
(c) Cold temperature, fish, length of days, climate and vegetation, etc.
(d) No because they are doing for their private profit and risking the lives of penguins.
(e) They seems to be money minder, selfish, etc.

In this page, we are providing Physical and Chemical Changes Class 7 Extra Questions and Answers Science Chapter 6 pdf download. NCERT Extra Questions for Class 7 Science Chapter 6 Physical and Chemical Changes with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 6 Extra Questions and Answers Physical and Chemical Changes

Extra Questions for Class 7 Science Chapter 6 Acids, Bases and Salts with Answers Solutions

Physical and Chemical Changes Class 7 Extra Questions Very Short Answer Type

Question 1.
What is the colour of the flame when magnesium is burnt?
Answer:
White

Question 2.
What kind of change is rusting?
Answer:
Chemical

Question 3.
Define galvanisation.
Answer:
The process of depositing a layer of zinc over iron is called galvanisation.

Question 4.
What is the meaning of rusting?
Answer:
The formation of rust over the surface of iron is known as rusting.

Question 5.
State two examples of physical changes.
Answer:
(i) Cutting a piece of paper
(ii) Melting of ice

Question 6.
Name the two main kinds of changes.
Answer:

• Physical
• Chemical

Question 7.
State the decomposition of calcium carbonate with the help of formulae and chemical reactions.
Answer:

Question 8.
Which gas is released when baking soda is mixed with vinegar?
Answer:
Carbon dioxide (Co2)

Question 9.
Name the ultimate colour of the solution when iron nails are dipped in the solution of copper sulphate.
Answer:
Green

Question 10.
What is the nature of aqueous solution of magnesium oxide?
Answer:
The aqueous solution of magnesium oxide is basic in nature, as it turns red litmus blue.

Question 11.
Define rust.
Answer:
Rust is a red or brown oxide coating on iron caused by the action of oxygen and moisture.

Question 12.
Is burning a physical change?
Answer:
No

Question 13.
Name the colour of copper sulphate solution.
Answer:
Blue

Question 14.
What type of change occur when iron reacts with copper sulphate?
Answer:
Chemical change

Question 15.
Name two important factors responsible for rusting.
Answer:

• Water (or moisture)
• Oxygen

Physical and Chemical Changes Class 7 Extra Questions Short Answer Type

Question 1.
Define crystallisation.
Answer:
The process of obtaining pure crystals of substances from their solution is called crystallisation.

Question 2.
What happens when carbon dioxide passes through lime water?
Answer:
When carbon dioxide passes through lime water, calcium carbonate is formed and lime water turns milky.

Question 3.
Name some physical properties of a substance.
Answer:
Shape, size, colour, state of a substance are some of its physical properties.

Question 4.
Give some examples of physical changes.
Answer:
Following are some examples of physical changes:

1. Melting of ice
2. Glowing of electric bulb
3. Change of water into steam
4. Cutting of a block of wood
5. Breaking of a glass tumbler

Question 5.
Give some examples of chemical changes.
Answer:
Following are some examples of chemical changes:

1. Curdling of milk
2. Burning of a piece of paper
3. Cooking of rice
4. Rusting of iron
5. Explosion of firecrackers

Question 6.
Explain the burning of magnesium ribbon.
Answer:
Take a thin ribbon of magnesium. Gently clean the end of the ribbon with sand paper and bring its tip near a candle flame. It is observed that the ribbon burns with a bright white light. After combustion, white powdery ash is left, which is called magnesium oxide.

Question 7.
Define chemical change. Give one example.
Answer:
A change in which one or more new substance(s) is/are formed is called a chemical change; e.g., burning of a matchstick.

Question 8.
What do you mean by physical change?
Answer:
A change in which a substance undergoes a change in its physical properties is called a physical change.

Question 9.
What are the characteristics of a chemical change?
Answer:
The characteristics of a chemical change are:

1. They release or absorb energy.
2. Most of the changes are irreversible.
3. One or more new substances with new properties are formed.
4. The properties of products are entirely different from the reactants.

Question 10.
Write some points about ozone layer.
Answer:

• It acts as a shield against the harmful radiations of the sun.
• Its chemical formula is o3.
• Ozone is entirely different from oxygen.

Physical and Chemical Changes Class 7 Extra Questions Long Answer Type

Question 1.
Why is the burning of a candle considered a chemical change?
Answer:
Candles are made of wax and a long thread of cotton (called wick of the candle). While candle is burnt, the molten wax goes up through the thread and undergoes combustion to form carbon dioxide and water vapour. The ‘wick’ of the candle gets changed to a black mass.

Over the process, heat and light energy is given out. It is not possible to
(i) recover the burnt wax again,
(ii) recover the thread again.
Hence, the burning of a candle is a chemical change.

Question 2.
State the differences between chemical and physical changes.
Answer:

Question 3.
What happens when iron nails are dipped in copper sulphate solution?
Answer:
When iron nails are dipped in copper sulphate solution, a brown layer of copper gets deposited on the surface of iron nails after some time. This happens due to the reaction between copper sulphate and iron. Also, the colour of copper sulphate changes from blue to green due to the formation of iron sulphate.

Question 4.
Most of the physical changes are reversible but some are irreversible. Explain the statement with examples.
Answer:
In physical change, a substance undergoes a change in its physical properties only. Physical change occurs when there is a force applied, change in temperature, etc., on a substance. Most of the physical changes are reversible like rolling a dough into a chapati and then again bringing back into a dough.

Making a toy aeroplane by folding the paper and then again unfolding the toy aeroplane to recover the page. But when a physical change cannot be reversed or we cannot bring the substance back to its original shape, size, state, etc., is known as irreversible change. For example, baking chapati or making a toy aeroplane by cutting the paper instead of folding it.

Question 5.
Give an example of a chemical reaction for each of the following situations:
(a) A change in colour is observed.
(b) A gas is evolved.
(c) Sound is produced.
(d) Heat is produced.
(e) Change in taste is observed.
(f) Light is produced.

Answer:
(a) Reaction between copper sulphate solution and iron metal. Blue colour of copper sulphate solution changes to green colour ferrous sulphate solution.
(b) Reaction between baking soda and vinegar evolves carbon dioxide gas.
(c) Burning of crackers produces sound.
(d) Reaction between hydrochloric acid and sodium hydroxide produces heat.
(e) Setting of curd from milk. Taste of milk changes to sour in curd.
(f) Burning of fuel produces light.

Physical and Chemical Changes Class 7 Extra Questions HOTS

Question 1.
When we keep a piece of iron in the open area for few days, a brownish, flaky substance, called rust, is deposited on it.
(a) Is rust different from iron?
(b) Is formation of rust from iron a chemical change?
(c) Can you change rust back into iron by some simple method?
(c) Give some other examples of a similar type of changes.

Answer:
(a) Yes. Rust is oxide of iron.
(b) Yes, it is a chemical change as properties of iron has changed.
(c) No.
(d) 1. Setting of curd into milk.
2. Burning of magnesium ribbon in air.
3. Cooking of food.

Question 2.
Why lime water turns milky on passing carbon dioxide gas into it?
Answer:
Chemical formula of lime water is calcium hydroxide which is a colourless solution. When we pass carbon dioxide gas into lime water, it forms white coloured insoluble calcium carbonate.
Lime water + Carbon dioxide ➝ Calcium carbonate + Water

Question 3.
Why iron pillar in Qutub Minar in Delhi famous?
Answer:
It is famous because it has not rusted though was built more than 1600 years ago.

Physical and Chemical Changes Class 7 Extra Questions Value Based (VBQs)

Question 1.
Sarita while helping her mother in kitchen work noticed that the slices of potato and brinjal have acquired a brown colour. She asked her mother reason behind this change. Her mother said whenever we keep cut pieces of these vegetables open for long time they acquire such colour.
(a) Are cutting vegetables and change in colour, physical or chemical changes?
(b) Why vegetables acquired brown colour?
(c) Do this brown colouration indicate that the vegetables are spoilt. Can we reverse this process? Why?
(d) Can you suggest ways to avoid this colouration of vegetables?
(e) What value of Sarita is shown here?

Answer:
(a) Cutting vegetables is physical change and change in colour of vegetables is chemical change.
(b) Vegetables acquire brown colour due to chemical reaction and thus, formation of new substance.
(c) No, vegetables are not spoilt and we cannot reverse this process because it is a chemical change.
(d) 1. By not keeping cut vegetables for long time to exposed air.
2. By dipping cut vegetables in cold water.
(e) Sarita is helping in nature, thoughtful and inquisitive.

Question 2.
Ramesh and Shyam both bought a big iron table for their shop individually. Ramesh painted his table with paints whereas Shyam got it laminated.
(a) What conditions are necessary for the process of rusting?
(b) Whose method is effective in preventing rusting? How?
(c) How rusting cause a great economic loss?
(d) What values of Ramesh and Shyam are shown here?

Answer:
(a) For rusting, moisture and oxygen is necessary.
(b) Both, Ramesh’s and Shyam’s methods are effective in preventing rusting. Painting and lamination, both, will prevent air and moisture from coming in contact with the iron table.
(c) Rusting cause a great economic loss as replacement of corroded equipment, their maintenance,
A contamination of other substances, etc., requires a huge amount to be spent on them.
(d) Ramesh and Shyam are both intelligent and responsible.

In this page, we are providing Acids, Bases and Salts Class 7 Extra Questions and Answers Science Chapter 5 pdf download. NCERT Extra Questions for Class 7 Science Chapter 5 Acids, Bases and Salts with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 5 Extra Questions and Answers Acids, Bases and Salts

Extra Questions for Class 7 Science Chapter 5 Acids, Bases and Salts with Answers Solutions

Acids, Bases and Salts Class 7 Extra Questions Very Short Answer Type

Question 1.
Give two examples of acidic substances.
Answer:
Lemon juice and vinegar.

Question 2.
Give two examples of basic substances.
Answer:
Lime water and baking soda.

Question 3.
What is the colour of litmus in distilled water?
Answer:
Mauve (purple) colour.

Question 4.
Name some substances in which tartaric acid is found?
Answer:
Tamarind, grapes, unripe mangoes, etc.

Question 5.
Which base is found in window cleaner?
Answer:
Ammonium hydroxide.

Question 6.
Give an example of an antacid.
Answer:
Milk of magnesia.

Question 7.
What makes the soil acidic?
Answer:
Excessive use of chemical fertilisers.

Question 8.
Which acid is injected into our skin when an ant bites?
Answer:
Formic acid.

Question 9.
What helps us to digest food?
Answer:
Hydrochloric acid helps us to digest food.

Question 10.
Name two types of litmus papers.
Answer:
Red litmus paper and blue litmus paper.

Question 11.
What colour does phenolphthalein give when the solution is basic?
Answer:
Pink

Question 12.
What neutralises the basic nature of the soil?
Answer:
Acids released by organic matter neutralises the basic nature of the soil.

Question 13.
When organic matter is added to the soil?
Answer:
If the soil is basic.

Question 14.
What substance is used to treat the soil when it is too acidic?
Answer:
Bases like quick lime or slaked lime.

Question 15.
What kills fish and other organism present in the water bodies?
Answer:
Releasing of factory wastes containing acids or bases.

Question 16.
What is nature of salt?
Answer:
It may be acidic, basic or neutral in nature.

Question 17.
What happens when an acidic solution is mixed with a basic solution?
Answer:
Both solution neutralises each other with the formation of salt, water and evolution of heat.

Question 18.
What is neutralisation?
Answer:
The reaction between an acid and a base is called neutralisation.

Question 19.
Name two natural indicator.
Answer:

• Litmus
• Turmeric Question

Question 20.
What is a neutral substance?
Answer:
The substance of solution which does not show any effect on litmus paper is called a neutral substance.

Question 21.
What is an acid?
Answer:
The substance having sour taste is called an acid.

Question 22.
What is a base?
Answer:
The substance having bitter taste and feels soapy on touching is called a base.

Acids, Bases and Salts Class 7 Extra Questions Short Answer Type

Question 1.
Explain the terms acids and acidic.
Answer:
The substances that taste sour are called acids, such as curd, lemon juice, orange juice, vinegar, etc. The chemical nature of these substances are acidic.

Question 2.
What are bases? What is their nature?
Answer:
The substances that taste bitter and feel soapy on touching are called bases; e.g., lime water, baking soda, washing soda, etc. The nature of these substances are basic.

Question 3.
What are indicators?
Answer:
Indicators are special type of substances that are used to test whether a substance is acidic or basic. They change their colour when added to a solution containing an acidic or a basic substance. For example, turmeric, China rose petals, litmus, etc., are naturally occurring indicators.

Question 4.
What is litmus?
Answer:
Litmus is the most commonly used natural indicator. It is extracted from lichens. It has mauve (purple) colour in distilled water when added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It may be in the form of a solution or in the form of strips of paper called litmus paper, which are generally red and blue.

Question 5.
What is neutralisation? Give an example of a neutralisation reaction.
Answer:
The reaction between an acid and a base is called neutralisation. In this process, salt and water are formed with the evolution of heat.
Acid + Base ➝ Salt + Water + (heat is evolved)
Here is a reaction showing neutralisation.

Question 6.
Why do you rub baking soda or calamine solution when an ant bites us?
Answer:
When an ant bites, it inject formic acid into our skin, which is painful and may be very harmful sometimes. The effect of the acid can be neutralised by rubbing moist baking soda, i.e., sodium hydrogen carbonate or calamine solution containing zinc carbonate.

Question 7.
How are the factory wastes neutralised?
Answer:
Many factory waste contain acids which kill fish and other organisms, if allowed to flow into the water bodies untreated. These wastes can be neutralised by adding basic substances to them.

Question 8.
What is salt?
Answer:
Salt is a substance obtained from the neutralisation reaction of an acid and a base.
Acid + Base ➝ Salt + Water + Heat
Salt may be acidic, basic or neutral depending on whether the acids or bases used to make salts are weak or strong.

Question 9.
What is meant by acid rain?
Answer:
The rain containing excess of acids is called acid rain. The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide, which are released into the air as pollutants, dissolve in rain water to form carbonic acid, sulphuric acid and nitric acid respectively. Acid rain can cause damage to buildings, historical monuments, plants and animals.

Acids, Bases and Salts Class 7 Extra Questions Long Answer Type

Question 1.
Explain the process of neutralisation with the help of an activity.
Answer:
When an acidic solution is mixed with a basic solution, both the solutions neutralise the effect of each other. The resulting solution is neither acidic nor basic. We can show the process of neutralisation with the help of an activity.

Fill one-fourth of a test tube with dilute hydrochloric acid. Note down its colour and also the colour of . phenolphthalein solution. Add 2-3 drops of the indicator to the acid. Shake the test tube gently. We observe that solution remains colourless. Add sodium hydroxide solution in the test tube drop by drop with continuous stirring till the pink colour just appears. Appearance of pink colour indicates that the neutralisation reaction has completed.

Question 2.
What are the applications of neutralisation reaction in everyday life?
Answer:
Neutralisation helps us in many ways in our everyday life. Some of the applications are:

1. Indigestion: When we suffer from acidity we take antacid to get relief. Antacid neutralises the effect of excessive acid.
2. Ant bite: When an ant bites, moist baking soda solution or calamine solution is rubbed which neutralises the effect of acid injected into the skin when an ant bites.
3. Soil treatment: Plants do not grow well when the soil is too acidic or too basic. When the soil is too acidic, it is treated with bases like quick lime or slaked lime and when it is basic, organic matter is added to it. Organic matter releases acids which neutralise the basic nature of the soil.
4. Factory wastes: The factory wastes contain acids, they are harmful for water bodies. To neutralise these wastes, basic substances are added to them.

Question 3.
Fill in the crossword given with the help of the clues provided.

Across
(2) The solution which does not change the colour of either red or blue litmus.
(4) Phenolphthalein gives pink colour in this type of solution.
(7) Colour of blue litmus in lemon juice.

Down
(1) It is used to test whether a substance is acidic or basic.
(3) It is natural indicator and gives pink colour in basic solution.
(5) Nature of ant’s sting.
(6) It is responsible for increase in temperature during a neutralisation reaction.
Answer:

Acids, Bases and Salts Class 7 Extra Questions HOTS

Question 1.
If we add dilute sulphuric acid to lime water, what will happen to the reaction mixture?
Answer:
The reaction mixture will become hot due to neutralisation reaction between sulphuric acid and lime water.

Question 2.
In a reaction given below, how can we get solid sodium chloride from its solution?
Hydrochloric acid + Sodium hydroxide ➝ Sodium chloride + Water
Answer:
Through the process of evaporation we can get solid sodium chloride from its solution. We must evaporate the water in a container over a burner until all the water from the mixture evaporates.

Question 3.
Shweta took a little sodium hydroxide in a beaker and dipped a red litmus paper into it. She observed red litmus paper turned blue.
She took dilute hydrochloric acid in the same beaker and dipped a blue litmus paper into it. The blue litmus paper did not turn red. Why?
Answer:
Shweta took dilute hydrochloric acid in the same beaker containing sodium hydroxide solution. Mixing of base into acid forms salt which is neutral and does not change colour of either blue or red litmus paper.

Question 4.
Why litmus is better natural indicator than other natural indicator?
Answer:
Litmus give wide range of colour change from weak acid to strong acid and from weak base to strong base. Other natural indicator, on the other hand, do not show a wide colour change.

Question 5.
Is it advisable to drink lemonade during indigestion? Why?
Answer:
No it is not advisable to drink lemonade during indigestion because it is acidic in nature. Too much acidity in stomach causes indigestion. Drinking lemonade may worsen the condition.

Acids, Bases and Salts Class 7 Extra Questions Value Based (VBQs)

During performing an experiment on neutralisation reaction, Ravi took about 100 mL of sodium hydroxide solution and pour approximately the same amount of concentrated hydrochloric acid to it.
He observed a very vigorous reaction with evolution of large amount of heat. When he dipped litmus paper into the solution it turned red. He was surprised with the result though he had read all the instructions and precautions given to him by his teacher.
(a) What was the expected result of the experiment?
(b) What went wrong in the experiment performed by Ravi?
(c) Why Ravi observed a very vigorous reaction with evolution of large amount of heat when he added concentrated hydrochloric acid to sodium hydroxide?
(d) What value of Ravi is shown here?
Answer:
(a) It was expected that the solution form will be neutral and would not change colour of the litmus.
(b) Ravi added concentrated hydrochloric acid instead of dilute hydrochloric acid. This mistake can prove very dangerous.
(c) Hydrochloric acid is a strong acid and sodium hydroxide is a strong base themselves to produce enough heat when mixed together. In addition to this, Ravi used concentrated form of this acid which can even cause burns.
(d) Ravi showed carelessness over here by not reading the instructions and precautions carefully before performing an experiment.

Question 2.
Class VII students went for an educational trip to see how various industries and human settlements around river Yamuna, in Delhi, is polluting it deliberately. They saw that factory wastes and municipal wastes are dumped into it untreated. They thought of spreading an awareness programme. They even wrote to Municipal Corporation of the state suggesting ways to reduce this kind of pollution.
(a) How factory or domestic wastes affect the quality of river?
(b) How the process of neutralisation is effective in changing some of the quality of water?
(c) Suggest any two ways to reduce pollution of river Yamuna.
(d) Why is it important to check river pollution?
(e) What methods will you adopt to spread awareness against river pollution?
Answer:
(a) Factory or domestic waste changes colour, turbidity, acidity or basicity, temperature, microbial growth, etc., of the water.
(b) If the river water is too acidic or basic, it can affect the aquatic life. So by neutralising the pollutants before discharging into the river can at least change water quality to neutral.
(c) Pollution of river Yamuna can be reduced largely by making the people aware that how can they contribute in their own level to control water pollution and giving strict guidelines to industries situated near river bank to treat their waste suitably before discharging it into the river.
(d) It is important to check river pollution because they are our lifeline. We all are dependent mainly on river water for various activities like drinking water, irrigation, fishing, etc. Pollution of river water also affect the aquatic life.
(e) We will make poster, do some street dramas, will write an article in newspaper or social sites and most important will follow the rules to minimise water pollution by ourselves.

In this page, we are providing Food Where Does it Come From Class 7 Extra Questions and Answers Science Chapter 4 pdf download. NCERT Extra Questions for Class 7 Science Chapter 4 Food Where Does it Come From with Answers will help to score more marks in your CBSE Board Exams.

Class 7 Science Chapter 4 Extra Questions and Answers Heat

Extra Questions for Class 7 Science Chapter 4 Heat with Answers Solutions

Heat Class 7 Extra Questions Very Short Answer Type

Question 1.
How does the transfer of heat take place in water or air?
Answer:
By the process of convection.

Question 2.
Write the range of laboratory thermometer.
Answer:
-10°C to 110°C

Question 3.
Name the process in which a solid directly changes into gas on heating.
Answer:
Sublimation

Question 4.
What is the range of a clinical thermometer?
Answer:
35°C to 42°C

Question 5.
Why do we wear woollen clothes during winter?
Answer:
The wool traps air in it which is a poor conductor of heat and hence it keeps us warm in winter.

Question 6.
Name the scales used to measure body temperature in humans.
Answer:
Celsius and Fahrenheit

Question 7.
Give any two examples of good conductors of heat.
Answer:
Silver, iron

Question 8.
Give an example of insulator.
Answer:
Plastic

Question 9.
Which physical state of matter expands the most on heating?
Answer:
Gas

Question 10.
What is the SI unit of temperature?
Answer:
Kelvin (K)

Question 11.
What are the various methods of transfer of heat?
Answer:

• Conduction
• Convection
• Radiation

Question 12.
Define conductor.
Answer:
A substance that readily conducts electricity or heat is called conductor.

Question 13.
Define insulator.
Answer:
A substance with negligible electrical or thermal conductivity is called an insulator.

Question 14.
What type of clothes should we wear in the summer?
Answer:
Light-coloured cotton clothes.

Question 15.
Define heat.
Answer:
Heat is a form of energy that is transferred by a difference in temperature between one object to another.

Heat Class 7 Extra Questions Short Answer Type

Question 1.
Define sea breeze.
Answer:
Sea breeze is the movement of air from the sea towards the land in coastal areas during day time. It is a cooling breeze.

Question 2.
Define land breeze.
Answer:
Land breeze is the movement of cool air from the land towards the sea in coastal areas during night.

Question 3.
State the effects of heat.
Answer:
Heat can bring many changes in an object. An object might expand on heating, as it becomes hotter. Heat can also cause a change in the state of a body. For example, on heating, ice(solid), eventually changes into water (liquid). Heat can burn an object or even kill harmful bacteria. It can also increase the speed of chemical reactions.

Question 4.
Write about clinical thermometer.
Answer:
A thermometer specifically designed for the measurement of the temperature of our body is called a clinical thermometer. It consists of a long, narrow glass tube. It has a bulb at one end, which contains mercury. It reads temperature from 35°C to 42°C.

Question 5.
What is laboratory thermometer?
Answer:
The thermometer which is used to measure the temperature of objects in laboratory is called a laboratory thermometer. Its range is -10°C to 110°C.

Question 6.
What are the differences between temperature and heat?
Answer:

Question 7.
Write any three precautions to be taken while reading a clinical thermometer.
Answer:

• Do not hold the thermometer by the bulb.
• Read the thermometer keeping the level of mercury along the line of sight.
• Ensure that before use the mercury level is below 35°C.

Question 8.
Can a clinical thermometer be used to measure the temperature of boiling water?
Answer:
No, a clinical thermometer cannot be used to measure the temperature of boiling water because the temperature of boiling water is more than the fixed range of the clinical thermometer, i.e., 42°C. If we try to measure the temperature of boiling water, it will break down.

Question 9.
Explain how the temperature of water can be measured by using a laboratory thermometer.
Answer:
To measure the temperature of water by using a laboratory thermometer, we follow the following steps:

1. Take water in a beaker.
2. Dip the laboratory thermometer in the water so that its bulb gets completely immersed in it, but make sure the bulb doesn’t touch the bottom of the beaker.
3. Hold the thermometer vertically.
4. Consider the movement of the thread of mercury.
5. After it becomes static, notice the reading.

Question 10.
Why is the handle of a metallic kettle covered with strips of cane?
Answer:
It is because when the kettle is heated the heat does not pass through strips of cane as these are bad conductors of heat and we can hold the handle barehanded.

Heat Class 7 Extra Questions Long Answer Type

Question 1.
What is temperature? Describe two types of thermometers used to measure the temperature.
Answer:
A reliable measure of the hotness of an object is called its temperature. It is measured by a device called thermometer.
There are two types of thermometer:
(i) Clinical thermometer: The thermometer that measures the temperature of our body is called clinical thermometer (Fig. 4.15). It consists of a long, narrow, uniform glass tube. It has a bulb at one end which contains mercury. Outside the bulb a small shining thread of mercury can be seen. There is also a scale on the thermometer. The scale used in it is the celsius scale, indicated by °C. A clinical thermometer reads temperature from 35°C to 42°C.

(ii) Laboratory thermometer: This type of thermometer is used to measure the temperature of different objects in laboratories. It is made of a thin glass tube sealed at one end and a bulb with mercury at the other end. The portion of the capillary tube above the bulb is graduated in degrees usually from -10°C to 110°C.

Question 2.
How is a thermometer read? What are the precautions to be observed while reading a clinical thermometer?
Answer:
First, note the difference of temperature indicated between the two bigger marks. Also note down the number of divisions (shown by smaller marks) between these marks. Suppose the bigger marks read one degree and there are five divisions between them. Then one small division can read \(\frac {1}{5}\) = 0.2°C.

Now wash the thermometer, preferably with an antiseptic solution. Hold it firmly and give it a few jerks to bring the level of mercury down to below 35°C. Now place the bulb of the thermometer under your tongue or armpit and take it out after one minute and note the reading. This is your body temperature. This should always be stated with its unit °C.

Some precautions one must observe while reading a clinical thermometer are:

1. It should be washed before and after use, preferably with an antiseptic solution.
2. It should be ensured that the mercury level is below 35°C before use.
3. It should be read keeping the level of mercury along the line of sight (Fig. 4.17)
4. The thermometer must be handled with care.
5. It should not be held by the bulb while reading.

Question 3.
What do you mean by transfer of heat? Explain the process of transfer of heat in solids, liquids and gases.
or
What do you mean by transfer of heat? Explain the process of transfer of heat.
Answer:
Flow of heat from one object to another whether solid or liquid is called transfer of heat. Heat always flows from a body at higher temperature to another body at lower temperature. In other words, heat always flows from a hotter body to a colder. In this process, the temperature of hot body falls as it releases heat which is received by the colder body or a body having lower temperatures. Thus the temperature of the colder body or less hotter body rises. The flow of heat stops when temperature of both the bodies becomes equal.

Transfer of heat take place through conduction, convection and radiation. Conduction is the process of transfer of heat from one particle to the next particle in a solid without the particles actually moving from their position.

Convection is the process of heat transfer in which the particles change their positions by constantly moving from the hotter region to the cooler region, thus causing heat energy to flow. In convection heat travels through the liquids and gases.

Radiation is the process of heat transfer from a hot body to a colder body without any medium between the two.

Question 4.
How does the heat travel in air? Explain the sea breeze and land breeze in coastal areas in this reference.
Answer:
Heat travels in air through the process of convection. The air near the heat source gets hot and rises up. The cool air from the sides comes in to take its place. In this way the air gets heated up.

In the coastal areas, people experience an interesting phenomenon. The land gets heated faster than the water during the day. The air over the land becomes hotter and rises up. The cooler air from the sea rushes in towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle.

The flow of cool air from the sea towards the land to replace the hot air on land, is called sea breeze. At night it is just the reverse: The water cools down more slowly than land. So the cool air from land moves toward the sea. This is called land breeze.

Question 5. Explain the term radiation.
or
Explain how can heat travel in vacuum or without medium.
Answer:
The heat from the sun cannot reach us by conduction or convection as there is no medium such as air in most part of the space between the earth and the sun. This is possible through the process of radiation. The mode of transfer of heat energy in which no medium is needed to transfer heat from a hotter body to a colder body is called radiation. It can take place whether a medium is present or not. For example, when we sit in front of a room heater we get heat by this process.

A hot utensil kept away from the flame cools down as it transfers heat to the surroundings by radiation. Our body too, gives heat to the surroundings and receives heat from it by radiation. The figure below show the radiation by the sun. It also shows that when radiation falls on an object a part of it is reflected, a part is absorbed and a part may be transmitted. (Fig. 4.19).

Question 6.
List any four effects of heat. Explain them.
Answer:
When heat energy is absorbed by a body various changes can happen. Some of them are:

1. Rise in temperature: When a body absorbs heat, it gains energy. As a result of this, temperature of the body rises and body becomes hot.
2. Change in state of matter: On heating, most of the substances change its state, like solid to liquid, liquid to gas, etc.
3. Expansion: All state of matter i.e., solid, liquid or gas expand on heating and contract on cooling. Expansion is most in gases, less in liquids and least in solids. Expansion due to heat is known as thermal expansion.
4. Combustion: On heating, some of the substance reach their ignition temperature and starts burning. So heat causes combustion.

Heat Class 7 Extra Questions HOTS

Question 1.
Why the level of mercury rises when its bulb comes in contact with a hot object?
Answer:
Mercury expands when it is heated. Hence, it rises in the capillary tube.

Question 2.
Shopkeepers selling ice blocks usually cover them with jute sacks or saw dust. Explain why.
Answer:
Jute sacks or saw dust act as insulating material and reduces melting of ice. Thus, blocks of ice are covered with jute sacks or saw dust.

Question 3.
While constructing a house in coastal area, in which direction should the windows preferably face and why?
Answer:
The windows preferably face towards the sea as sea breeze will keep the house cool in day time.

Question 4.
Why are milk vans carrying milk from the factory to the depots painted silver or white?
Answer:
Milk vans are painted silver or white because white absorbs minimum light or reflects maximum light and thus keep the milk fresh.

Question 5.
Ventilators are situated close to the ceilings and not near the floor. Why?
Answer:
Warm air being lighter rises up and cool air takes it place. This warm air finds its exit from the ventilators located close to ceilings and thus helps in circulation of fresh air.

Heat Class 7 Extra Questions Value Based (VBQs)

Question 1.
Sarika likes to have curd in her lunch. She even knows that for setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting the curd, if the temperature of the mixture remains approximately between 35°C to 40°C. But she is worried because it is winter and the room temperature remains much below the range which makes setting of curd difficult.
(a) Suggest a way to Sarika to set curd in such a situation.
(b) Why setting of curd during winter season become difficult?
(c) Is eating curd good for health?
(d) What value of Sarika is shown here?
Answer:
(a) Sarika can set curd by

• Keeping the container wrapped in woollen material or inside a heat resistant container.
• Keeping the container near the gas stove while cooking.

(b) In winter season temperature is very low. Low temperature inhibits the activity and growth of microbes present in curd and thus makes setting of curd difficult.
(c) Yes, as eating curd helps in digestion, boost our immunity and gives us many nutrients required for our growth.
(d) Sarika is an intelligent girl with good food habits but she lacks a little information about how insulators can help to keep things warm.

Question 2.
Ramjas lived in an old house. His father thought of reconstructing the house. He brought a new house plan design to home to show it to every family member. Ramjas pointed out that the house lack ventilators and he is unhappy for that.
(a) Are ventilators important? Why?
(b) In summer, which colour will you choose to paint outer wall of your house?
(c) What value of Ramjas is shown here?

Answer:
(a) Yes. A ventilator helps in circulating fresh and cool air from outside and taking out stale and warm air from the room. Thus, it helps in maintaining the quality of air.
(b) In summer, I would like to paint outer wall with lighter colour to reflect most of the heat and keeping house cool.
(c) Ramjas is thoughtful, intelligent, health conscious with scientific aptitude.