Access to the AP 7th Class Science Study Material 3rd Lesson Heat Questions and Answers are aligned with the curriculum standards.
AP 7th Class Science 3rd Lesson Heat Questions and Answers
AP Board Solutions Class 7 Science Chapter 3 Heat
Exercise
Question 1.
State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Similarities :
- Both thermometers consists of a long, narrow uniform glass tubes.
- Both contains mercury in bulb.
- Both have a bulb at one end.
- Both have the celsius or centigrade scale for temperature measurement.
Differences:
- Clinical thermometer is used to measure the human body temperature whereas laboratory thermometer is used to measure the temperature of different objects other than human body.
- Kink is present in clinical thermometer while kink is absent in laboratory thermometer
- Clinical thermometer reads temperature between 35°C to 42°C while the range of a laboratory thermometer is -10°C to 110°C.
Question 2.
Give two examples each of conductors and insulators of heat.
Answer:
Conductors: Iron, Copper, Aluminium.
Insulators : Wood, Plastic.
3. Fill in the blanks:
a) The hotness of an object is determined by its ………….
b) Temperature of boiling water cannot be measured by a ………… thermometer.
c) Temperature is measured in degree …………
d) No medium is required for transfer of heat by the process of ………….
e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of …………
f) Clothes of ………… colours absorb more heat better than clothes of light colours.
Answer:
a) Temperature
b) Clinical
c) Celsius
d) Radiation
e) Conduction
f) Dark/black
4. Match the following:
i) Land breeze blows during — a) summer
ii) Sea breeze blows during — b) winter
iii) Dark coloured clothes are preferred during — c) day
iv) Light coloured clothes are preferred during — d) night
Answer:
i) Land breeze blows during — d) night
ii) Sea breeze blows during — c) day
iii) Dark coloured clothes are preferred during — b) winter
iv) Light coloured clothes are preferred during — a) summer
Question 5.
Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer:
Wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because air gets trapped in between layer. Air is a poor conductor of heat. This increases the insulation and thus becomes more comfortable to us by keeping us warm.
Question 6.
Look at Figure. Mark where the heat is being transferred by conduction, by convection and by radiation.
Answer:
Question 7.
In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Answer:
Objects with white surface reflect most of the heat and absorb less. So, less heat from outside would enter the house through walls.
Question 8.
One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be
a) 80°C
b) more than 50°C but less than 80°C
c) 20°C
d) between 30°C and 50°C
Answer:
d) between 30°C and 50°C
Question 9.
An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will:
a) flow from iron ball to water.
b) not flow from iron ball to water or from water to iron ball.
c) flow from water to iron ball.
d) increase the temperature of both.
Answer:
b) not flow from iron ball to water or from water to iron ball.
Question 10.
A wooden spoon is dipped in a cup of ice cream. It s other end
a) becomes cold by the process of conduction.
b) becomes cold by the process of convection.
c) becomes cold by the process of radiation.
d) does not become cold.
Answer:
d) does not become cold.
Question 11.
Stainless steel pans are usually provided with copper bottoms. The reason for this could be that:
a) copper bottom makes the pan more durable.
b) such pans appear colourful.
c) copper is a better conductor of heat than the stainless steel.
d) copper is easier to clean than the stainless steel.
Answer:
c) copper is a better conductor of heat than the stainless steel.
Questions given in the lesson
Page No. 48
Question 1.
In our day-to-day life, we come across a number of objects. Some of them are hot and some of them are cold. Tea is hot and Ice Is cold. List some objects you use commonly In Table. Mark these objects as hot or cold.
| Hot and cold objects | ||
| Object | Cold/Cool | Warm/Hot |
| Ice cream | ||
| Spoon in a tea cup | ||
| Fruit Juice | ||
| Handle of a frying pan | ||
Answer:
| Hot and cold objects | ||
| Object | Cold/Cool | Warm/Hot |
| Ice cream | ✓ | |
| Spoon in a tea cup | ✓ | |
| Fruit Juice | ✓ | |
| Handle of a frying pan | ✓ | |
Page No.50
Question 2.
Boojho says,”My left hand tells me that the water in mug C is hot and the right hand tells me that the same water is cold. What should I conclude?”
Answer:
Both of the conclusions are true relative to each hand. But a single conclusion cannot be drawn from the given information.
Question 3.
Boojho wondered which of the two scales shown in Figure he should read. Paheli told him that India has adopted the celsius scale and we should read that scale. The other scale with the range 94 -108 degrees is the Fahrenheit scale (°F). It was in use earlier.
Answer:
India has adopted the Celsius scale and we should read this scale. The other scale is Fahrenheit scale (°F) with the range of 94 – 108 degrees. Earlier, Farhenheit scale was in use. Now we use celsius scale.
Page No. 52
Question 4.
Paheli measured her body temperature. She got worried as it was not exactly 37°C
Answer:
Body temperature varies from person to person. It may be slightly higher for some people and may be lower for individual one.This is because a normal temperature of body which is 37°C is actually just an average temperature of a large number of healthy persons.
Page No. 54
Question 5.
Boojho got a naughty idea. He wanted to measure the temperature of hot milk using a clinical thermometer. Paheli stopped him from doing so.
Answer:
The clinical thermometer is designed to measure the temperature of human body only. A clinical thermometer can measure only between 35°C to 42°C. Beyond 42°C the mercury will not move further. Hot milk has very high temperature which cannot be measured by clinical thermometer. It may break. So, Paheli did good by stopping him from doing so.
Page No. 56
Question 6.
Boojho now understands why clinical thermometer cannot be used to measure high temperatures. But still wonders whether a laboratory thermometer can be used to measure his body temperature.
Answer:
A laboratory thermometer also cannot be used to measure the temperature of body due to the absence of the kink above its bulb. It prevents mercury level from falling on its own.
Question 7.
Boojho wonders why the level of mercury should change at all when the bulb of the thermometer is brought in contact with another object?
Answer:
When the bulb of the thermometer is brought in contact with other object mercury present in the bulb expands on taking heat of the object and thus the level of the mercury changes.
Page No. 58
Question 8.
Paheli asks: “Does it mean that heat will not be transferred if the temperature of two objects is the same?
Answer:
Yes, heat will not transfer if both objects are at same temperature.
Extended Learning – Activities and Projects
Question 1.
Go to a doctor or your nearest health centre. Observe the doctor faking temperature of patients. Enquire:
a) why she dips the thermometer in a liquid before use.
b) why the thermometer is kept under the tongue.
c) whether the body temperature can be measured by keeping the thermometer at some place other than the mouth.
d) whether the temperature of different parts of the body is the same or different. You can add more questions which come to your mind.
Answer:
a) The doctor dips the thermometer in a liquid before use. It is done that the infections of the previous person who used the thermometer is removed.
b) The thermometer is kept under the tongue because the intense heat of our body is present under our tongue.
c) We can measure the temperature of the body by keeping the thermometer at some places other than mouth like armpit.
d) The temperature of different parts is not same and it varies with different body parts.
Question 2.
Go to a veterinary doctor (a doctor who treats animals). Discuss and find out the normal temperature of domestic animals and birds.
Answer:
The normal temperature of domestic animals and birds are recorded as follows :
- The normal temperature of Goat varies from 39°C.
- The normal temperature of a dog is about 38.3°C
- The normal temperature of a pigeon (bird) is 40°C
- The normal temperature of a cat is 38°C
- The normal temperature of a duck is 40.7°C
- The normal temperature of a parrot is 41°C
- The normal temperature of a cow is 38.9°C
- The normal temperature of a parrot is 39.3°C
Question 3.
Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation.
Answer:
No, the paper does not burn. Iron is a good conductor of heat it absorbs the heat and doesn’t allow the paper to burn.
Question 4.
Take a sheet of paper. Draw a spiral on it as shown in the Figure. Cut out the paper along the line. Suspend the paper as shown in Figure above a lighted candle. Observe what happens. Think of an explanation.
Answer:
When the spiral paper is suspended at flame, then the paper spiral will keep moving because due to convection process, there will be transfer of heat and the air present above the flame will move up which results in movement of paper spiral.
Question 5.
Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a postcard. Press the postcard firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the postcard. Observe what happens. Explain.
Answer:
It can be observed that the colour of hot water initially rises up and the colour cold water sinks down at the bottom of the first bottle. Gradually, they mixed together to form a uniform colour and temperature. This demonstrate the process of convection.
Activities
Activity 3.1 Page No: 48
Question 1.
Take three small tubs/containers. Label them as A, B and C. Put cold water in container $A$ and hot water in container B. Mix some cold and hot water in container C. Now dip your left hand in container $A$ and the right hand in container B. After keeping the hands in the two containers for 2-3 minutes, put both the hands simultaneously in container C (Figure). Do both the hands get the same feeling?
Answer:
Aim : To find the degree of hotness or coldness by the sense of touch.
Materials required : Three small containers, cold water, hot water.
Procedure:
- Take three small containers.
- Label them as A, B and C . Put cold water in container A and hot water in container B.
- Mix some cold and hot water in container C.
- Now dip your left hand in container A and the right hand in container B.
- After keeping the hands in the two containers for 2-3 minutes, put both the hands simultaneously in container C .
Observation : We observe when we dipped the hands in two containers we feel different in both hands. The right hand feels the water is cool while the left hand feels the water warmer. It means that the touch sensory organs gives the relative responses to the temperature. Therefore, it is required to use a device to measure the temperature of a body. Conclusion : From the above activity, we can conclude that sense of touch fails to give an exact estimation of degree of hotness of a body.
Activity 3.2 Page No: 50
Question 2.
Let us learn how to read a thermometer. First, note the temperature difference 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 1/5 = 0.2°C.
Wash the thermometer, preferably with an antiseptic solution. Hold it firmly and give it a few jerks. The jerks will bring the level of mercury down. Ensure that it falls below 35°C. Now place the bulb of the thermometer under your tongue. After one minute, take the thermometer out and note the reading. This is your body temperature. The temperature should always be stated with its unit, °C
What did you record as your body temperature?
Answer:
A clinical thermometer measures the temperature between 35°C to 42°C. Its mercury level expands on an increase in temperature. We see this rise as a temperature level.
We should first clean the thermometer using soap or sanitizer and shake it vigorously so that mercury level drops below 35°C. Then we should place it below the tongue for 2-3 minutes. During this time mercury level rises as per the body temperature. Now, we should put the thermometer in front of the eye and should examine it throughly.
A mercury thermometer has linings between the two points. If the two-point have a one-degree difference, and between them, there are ten lines, then one line indicates 0.1°C.
Activity 3.3 Page No: 52
Question 3.
Measure the body temperature of some of your friends (at least 10) with a clinical thermometer. Record your observations as in Table.
| Name | Temperature (°Q) |
Answer:
Aim : To measure the body temperature of some of your friends.
Materials required : Clinical thermometer
Observations: The normal temperature of human body is 37°C.The temperature of human body normally does not go below 35°C or above 42°C. Most of friends will have their body temperature in this range. It could be slightly higher In case of fever or slightly lower In case of any illness.
| Name | Temperature (°C) |
| Ramesh | 37.2°C |
| Priya | 37°C |
| Ganesh | 38 °C |
| Pavitra | 36.8°C |
| Radha | 39°C |
| Harsha | 37.3°C |
| Rekha | 37°C |
| Mohith | 36.9°C |
| Surya | 37.9°C |
| Rao | 36.8°C |
Conclusion : From the above activity, we can conclude the temperature of every person may not be 37°C.This is because a normal temperature of body which is 37°C is actually just an average temperature of a large number of healthy persons. It could be slightly higher or slightly lower.
Activity 3.4 Page No : 54
Question 4.
Take some tap water in a beaker or a mug. Dip the thermometer in water so that the bulb is immersed in water but does not touch the bottom or the sides of the container. Hold the thermometer vertically (Figure). Observe the movement of mercury in the thermometer. Wait till the mercury thread becomes steady. Note the reading. Compare the temperature of water recorded by each student in the class.Are there any variations in the readings? Discuss the possible reasons.
Answer:
Aim : To measure temperature using laboratory thermometer. Materials required : Tap water, beaker, laboratory thermometer.
Procedure :
- Take some tap water in a beaker or a mug.
- Dip the thermometer in water so that the bulb is immersed in water but does not touch the bottom or the sides of the container.
- Hold the thermometer vertically (Figure).
- Observe the movement of mercury in the thermometer.
- Wait till the mercury thread becomes steady.
- Note the reading.
Observations: We observe that the temperature of the tap water is 38°C. The mercury level starts to fall as soon as we take out the thermometer from the water.
Question 5.
Take some hot water in a beaker or a mug. Dip the thermometer in water. Wait till the mercury thread becomes steady and note the temperature. Now take out the thermometer from water. Observe carefully what happens now.
Answer:
Aim : To measure that the temperature of hot water is much higher than the room temperature.
Materials required : Hot water, thermometer.
Procedure :
- Take some hot water in a beaker or a mug.
- Dip the thermometer in water.
- Wait for mercury thread becomes steady.
- Note the temperature.
- Now remove the thermometer from water.
Observation : We observe that the level of mercury falls as soon as thermometer is taken out from water.
Conclusion : From the above activity we can conclude that the temperature of hot water is much higher than the room temperature the level of mercury rises but when it is removed from the beaker, the mercury level starts descending as the temperature of the room is less than the temperature of hot water.
Activity 3.6 Page No: 58
Question 6.
Take a rod or flat strip of a metal, say of aluminium or Iron. Fix a few small wax pieces on the rod. These pieces should be at nearly equal distances. Clamp the rod to a stand. If you do not find a stand, you can put one end of the rod in between bricks. Now, heat the other end of the rod and observe.
Answer:
Aim : To demonstrate the process of conduction.
Materials required : Iron rod, few wax pieces, clamp stand.
Procedure:
- Take a rod or flat strip of a metal, say of aluminium or iron.
- Fix a few small wax pieces on the rod.
- These pieces should be at nearly equal distances (Figure).
- Clamp the rod to a stand. Flow of heat through a metal strip
- If you do not find a stand, you can put one end of the rod in between bricks.
- Now, heat the other end of the rod.
- Record your observations.
Observations : We observe when we heat the rod the wax pieces start to melt and fall down.The piece nearest to the flame fall first and the pieces which are far to the flame falls last.
Conclusion : From the above activity, we can conclude that the heat is transferred from the end nearest to the flame to the other end. Based on the activity answer the questions
i) What happens to the wax pieces ?Do these pieces begin to fall?
Answer: Yes, the wax pieces start to melt and fall down.
ii) Which piece falls the first?
Answer: The piece nearest to the flame fall first.
iii) Do you think that heat is transferred from the end nearest to the flame to the other end?
Answer: Yes, heat is transferred from the end nearest to the flame to the other end.
Activity 3.7 Page No: 60
Question 7.
Heat water in a small pan or a beaker. Collect some articles such as a steel spoon, plastic scale, pencil and divider. Dip one end of each of these articles in hot water. Wait for a few minutes. Touch the other end. Enter your observation in Table.
Answer:
Aim : To show the conduction of heat by different materials.
Materials required : Beaker, steel spoon, plastic scale, pencil and divider.
Procedure:
- Heat water in a small pan or a beaker.
- Collect some articles such as a steel spoon, plastic scale, pencil and divider.
- Dip one end of each of these articles in hot water (Figure).
- Wait for a few minutes.
- Touch the other end.
- Record your observations in table.
Observations: We observe pencil and scale are being insulators they do not become heat at the other end.
| Articles | Material with which the article is made of | Does the other end get hot Yes/No |
| Steel spoon | Metal | Yes |
| Scale | Plastic | No |
| Pencil | Wood | No |
| Divider | Steel | Yes |
Steel spoon and divider are the conductors of heat and the other tip become heated.
Conclusion: From the above activity we can conclude that the materials which allow heat to pass through them easily are conductors of heat.The materials which do not allow heat to pass through them easily are poor conductors of heat and also known as insulators.
Activity 3.8 Page No: 60
Question 8.
Take a round bottom flask (if flask is not available, a beaker can be used). Fill it two thirds with water. Place it on a tripod, or make some arrangement to place the flask in such a way that you can heat it by placing a candle below it. Wait till the water in the flask is still. Place a crystal of potassium permanganate at the bottom of the flask gently using a straw. Now, heat the water by placing the candle just below the crystal. Write your observation in your notebook and also draw a picture of what you observe.
Answer:
Aim : To show the convection of heat in water.
Materials required: Round bottom flask, water, tripod stand, candle, potassium permanganate crystals, straw.
Procedure:
- Take a round bottom flask (if flask is not available, a beaker can be used). Fill it two-thirds with water.
- Place it ory a tripod, or make some arrangement to place the flask in such a way that you can heat it by placing a candle below it.
- Wait till the water in the flask is still.
- Place a crystal of potassium permanganate at the bottom of the flask gently using a straw.
- Now, heat the water by placing the candle just below the crystal.
Observation : We observe when water is heated, the water near the flame gets hot. Hot water rises up. The cold water from the sides moves down towards the source of heat. This water also gets hot and rises and water from the sides moves down. This process continues till the whole water gets heated.
Conclusion : From the above activity we can conclude that the convection is the process of transferring from hotter region to cooler region by actual movement of particles. It generally occur in liquid and gaseous medium.
Activity 3.9 Page No: 62
Question 9.
Light a candle. Keep one hand above the flame and one hand on the side of the flame. Do your hands feel equally hot? If not which hand feels hotter? And why?
Answer:
Aim : To show the transfer of heat by convection in air.
Materials required : A candle.
Procedure:
- Light a candle.
- Keep one hand above the flame and one hand on the side of the flame.
Observations: We observe the hand key above the flame feels quite hot, but the hand kept on the side of the flame does not feel so hot.
Conclusion: From the above activity, we can conclude the hand about the flame feels hotter since air gets heated by the convection and rises up. On the other hand, that air on the side does not feel as hot because there is no convection.
Activity 3.10 Page No: 64
Question 10.
Take two identical tin cans. Paint the outer surface of one black and of the other white. Pour equal amounts of water in each and leave them in the mid-day sun for about an hour. Measure the temperature of water in both the cans. Do you find any difference in the temperatures? In which can is the water warmer?
Answer:
Aim: To show the difference in the temperature.
Materials required : Two identical tin cans, water, black and white paints.
Procedure:
- Take two identical tin cans.
- Paint the outer surface of one black and of the other white.
- Pour equal amounts of water in each and leave them in the midday sun for about an hour.
- Measure the temperature of water in both the cans.
Observations: We observe the one with black paint gets heated first. It is because black coloured surface absorbs more heat than white surface.
Conclusion : From the above activity we can conclude that dark surfaces absorb more heat and light colour surfaces reflect most of the heat.
Activity 3.11 Page No: 66
Question 11.
Fill the two cans used in Activity 3.10 with the same amount of hot water at the same temperature (say, at 60°C). Leave the cans in a room or in a shade. Note the temperature of water after 10 – 15 minutes. Does the temperature of water in both the cans fall by the same amount?
Answer:
Aim : To show the difference in the temperature.
Materials required : Two identical tin cans, hot water.
Procedure:
- Fill the two cans with the same amount of hot water at the same temperature (say, at 60°C ).
- Leave the cans in a room or in a shade.
- Note the temperature of water after 10-15 minutes,
Observation : We observe the container with white surface is relatively colder.
Conclusion : From the above activity we can conclude that dark surfaces absorb more heat and light colour surfaces reflect most of the heat.