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HEAT: EXERCISE QUESTIONS AND ANSWERS
Class 7 ICSE Physics
Learn, practise and revise the chapter Heat with step-by-step solutions and clickable answers.
MCQs Fill in the Blanks Numericals HOTS RevisionHow to Use This Practice Page
- Read each question carefully.
- Try to answer it independently in your notebook.
- Click the Show Answer button to check your response.
- Read the explanation, especially for numericals and application questions.
- Revise the questions you answered incorrectly.
Study challenge: Try answering every question before
revealing the solution. This will help you prepare more effectively
for your Physics examination.
A. Objective Questions: Choose the Correct Answer
1. Heat is measured in:
Correct answer: (d) Joule.
The SI unit of heat energy is the joule (J). Celsius, Kelvin and Fahrenheit are units used to express temperature.
The SI unit of heat energy is the joule (J). Celsius, Kelvin and Fahrenheit are units used to express temperature.
2. Convert 90°C into Fahrenheit.
Correct answer: (b) 194°F.
°F = (9/5 × °C) + 32
Substituting 90°C:
°F = (9/5 × 90) + 32
°F = 162 + 32
°F = 194°F
3. Which of the following is a flammable substance?
Correct answer: (d) All of these.
Wood, paper and LPG can burn under suitable conditions. Combustion requires fuel, oxygen and a sufficient ignition temperature.
Wood, paper and LPG can burn under suitable conditions. Combustion requires fuel, oxygen and a sufficient ignition temperature.
4. Which material is commonly used to make cooling coils
in refrigerators and air conditioners?
Correct answer: (a) Copper.
Copper is a good conductor of heat. Copper tubing is commonly used in refrigeration and air-conditioning systems, although other materials are also used in modern designs.
Copper is a good conductor of heat. Copper tubing is commonly used in refrigeration and air-conditioning systems, although other materials are also used in modern designs.
5. A land breeze blows from:
Correct answer: (a) Land to sea.
At night, land usually cools faster than the sea. The air above the relatively warmer sea rises, and cooler air flows from the land towards the sea. This movement produces a land breeze.
At night, land usually cools faster than the sea. The air above the relatively warmer sea rises, and cooler air flows from the land towards the sea. This movement produces a land breeze.
B. Fill in the Blanks
1. Sea breeze is caused due to __________ currents in nature.
Answer: Convection.
Uneven heating of land and sea produces convection currents in the air, causing sea breezes during the day.
Uneven heating of land and sea produces convection currents in the air, causing sea breezes during the day.
2. The amount of heat emitted by a body depends on its
__________.
Answer: Nature of its surface.
The amount of heat radiated depends on factors such as the surface's nature, area and temperature. Dark, dull surfaces are generally better emitters than shiny, polished surfaces at the same temperature.
The amount of heat radiated depends on factors such as the surface's nature, area and temperature. Dark, dull surfaces are generally better emitters than shiny, polished surfaces at the same temperature.
3. The heat from the Sun's rays reaches us by __________.
Answer: Radiation.
Radiation can transfer heat through a vacuum. Conduction and convection require a material medium.
Radiation can transfer heat through a vacuum. Conduction and convection require a material medium.
4. The burning of substances due to heat in the presence of
air or oxygen is termed as __________.
Answer: Combustion.
Combustion is a chemical reaction in which a substance reacts with oxygen and releases energy, usually as heat and often light.
Combustion is a chemical reaction in which a substance reacts with oxygen and releases energy, usually as heat and often light.
5. The increase in the size of an object due to heating
is called __________.
Answer: Thermal expansion.
Most solids, liquids and gases expand when heated and contract when cooled.
Most solids, liquids and gases expand when heated and contract when cooled.
C. Match the Following
Match each item in Column A with the correct description in Column B.
Column A
- Particles of the medium do not play any role
- Room heaters
- Actual movement of particles of the medium
- Thermos flask
- No actual movement of particles of the medium
- Minimises the transfer of heat to or from the stored substance
- Conduction
- Radiation
- Heat can be reflected more efficiently
- Convection
Correct matching:
- Particles of the medium do not play any role — Radiation (c)
- Room heaters — Radiation (d, in the textbook's intended sense)
- Actual movement of particles of the medium — Convection (e)
- Thermos flask — Minimises heat transfer (a)
- No actual movement of particles of the medium — Conduction (b)
D. True or False
1. The SI unit of temperature is calorie.
Answer: False.
The SI unit of temperature is kelvin (K). The calorie is a unit of energy.
The SI unit of temperature is kelvin (K). The calorie is a unit of energy.
2. The flow of heat continues until there is thermal equilibrium.
Answer: True.
Heat flows spontaneously from a region of higher temperature to a region of lower temperature. Net heat transfer stops when thermal equilibrium is reached.
Heat flows spontaneously from a region of higher temperature to a region of lower temperature. Net heat transfer stops when thermal equilibrium is reached.
3. Cloudy days are much hotter during the summer.
Answer: False as a general statement.
Clouds reflect and absorb some incoming solar radiation, which can reduce daytime heating. However, cloud cover can also increase humidity and reduce heat loss. The actual temperature depends on weather conditions.
Clouds reflect and absorb some incoming solar radiation, which can reduce daytime heating. However, cloud cover can also increase humidity and reduce heat loss. The actual temperature depends on weather conditions.
4. Heat travels in the form of electromagnetic waves.
Answer: True, for heat transfer by radiation.
Thermal radiation is electromagnetic radiation. Conduction and convection transfer heat by different mechanisms.
Thermal radiation is electromagnetic radiation. Conduction and convection transfer heat by different mechanisms.
5. In factories, chimneys are mounted below furnaces.
Answer: False.
Chimneys are generally placed above furnaces or combustion areas so that hot gases and smoke can rise and escape.
Chimneys are generally placed above furnaces or combustion areas so that hot gases and smoke can rise and escape.
E. Quick Check: Heat Transfer and Thermos Flask
1. Water is heated when kept on the stove by conduction.
True or false?
Answer: False as a description of the whole process.
Heat is conducted through the metal utensil. Water is heated mainly by convection currents within it, although conduction also occurs.
Heat is conducted through the metal utensil. Water is heated mainly by convection currents within it, although conduction also occurs.
2. Heat flows from the warmer part of a solid object to its
cooler part by convection. True or false?
Answer: False.
Heat travels through a solid mainly by conduction. Convection requires the bulk movement of a fluid.
Heat travels through a solid mainly by conduction. Convection requires the bulk movement of a fluid.
3. We receive heat from a fire by radiation. True or false?
Answer: True.
We can feel radiant heat from a fire even without touching it. Hot air may also transfer heat by convection.
We can feel radiant heat from a fire even without touching it. Hot air may also transfer heat by convection.
4. Dark or black bodies are generally good emitters of heat.
True or false?
Answer: True.
Dark, dull surfaces are generally good emitters and absorbers of thermal radiation.
Dark, dull surfaces are generally good emitters and absorbers of thermal radiation.
5. A thermos flask minimises the transfer of heat to or from
the liquid stored in it. True or false?
Answer: True.
The vacuum between the walls reduces conduction and convection. Reflective surfaces reduce heat transfer by radiation. The insulating stopper reduces heat transfer through the opening.
The vacuum between the walls reduces conduction and convection. Reflective surfaces reduce heat transfer by radiation. The insulating stopper reduces heat transfer through the opening.
F. Subjective Questions
1. Distinguish between heat and temperature.
Answer:
| Heat | Temperature |
|---|---|
| Heat is energy transferred because of a temperature difference. | Temperature indicates how hot or cold a body is. |
| Its SI unit is joule (J). | Its SI unit is kelvin (K). |
| Heat is transferred from higher to lower temperature. | Temperature determines the direction of spontaneous heat transfer. |
2. Describe the various effects of heat on matter.
Answer:
Heat can produce several effects.
- Change in temperature: Heating usually raises the temperature of a body.
- Change in state: Heat can melt a solid or change a liquid into vapour. Removing heat can cause condensation or freezing.
- Change in size: Most solids, liquids and gases expand when heated.
- Chemical change: Heat can help bring about chemical reactions, such as cooking food or burning wood.
- Combustion: When a combustible substance reaches its ignition temperature in the presence of oxygen, it may catch fire.
3. A wind is an example of a convection current in the
atmosphere. Explain.
Answer:
The Sun heats different parts of Earth's surface unequally.
Air above a warmer region becomes warmer and generally less
dense, so it rises. Cooler, denser air moves in to replace it.
This movement produces convection currents in the atmosphere.
Differences in atmospheric pressure and Earth's rotation also
influence winds.
4. Why are the bottoms of cooking utensils painted black?
Answer:
Black, dull surfaces are good absorbers of thermal radiation.
A blackened bottom can therefore absorb radiant heat efficiently
from a flame. Actual cooking efficiency also depends on the
utensil material, burner design and contact with the flame.
5. What are the advantages of a mercury thermometer?
Answer:
- Mercury expands fairly uniformly with temperature, allowing a scale with nearly equal intervals.
- Mercury has a high boiling point of approximately 357°C.
- Mercury remains liquid down to approximately −39°C.
- It does not wet the glass, so it forms a distinct column that is comparatively easy to read.
- Its shiny, opaque appearance makes the column easy to see.
G. Numericals: Step-by-Step Solutions
Remember these conversion formulas:
°F = (9/5 × °C) + 32
°C = (5/9) × (°F − 32)
K = °C + 273
For school-level calculations, the Celsius-to-kelvin conversion
is commonly performed using 273. More precise work uses 273.15.
1. Convert 59°F into °C.
Solution:
°C = (5/9) × (°F − 32)
Substitute 59°F:
°C = (5/9) × (59 − 32)
°C = (5/9) × 27
°C = 15°C
Final answer: 15°C.
2. Convert 125°C into kelvin.
Solution:
K = °C + 273
K = 125 + 273
Final answer: 398 K.
3. Convert 90°C into Fahrenheit.
Solution:
°F = (9/5 × 90) + 32
°F = 162 + 32
Final answer: 194°F.
H. Exemplar Problems: Apply Your Concepts
1. Can an alcohol thermometer be used to measure the
temperature of boiling water? Give a reason.
Answer: No, not a conventional alcohol thermometer.
Alcohol boils at approximately 78°C under normal atmospheric
pressure. Since boiling water is approximately 100°C, the
alcohol would boil before it could measure the temperature
reliably.
A suitably designed thermometer using a different sensing
material or technology is needed for this temperature.
2. Why does the level of mercury rise when its bulb comes
in contact with a hot object?
Answer:
The mercury receives heat and expands. Its volume increases,
so the mercury rises through the narrow capillary tube.
3. Why are milk vans carrying milk from factories to depots
painted silver or white?
Answer:
Light-coloured and shiny surfaces generally absorb less solar
radiation than dark, dull surfaces. Silver or white paint
therefore helps reduce heating of the milk van in sunlight.
Insulation and refrigeration are also important for keeping
the milk cool.
4. Which will cool faster: water kept in a black pot or
water kept in a silver pot?
Answer: Generally, the black pot.
A black, dull surface is a better emitter of thermal radiation
than a shiny silver surface at the same temperature.
Therefore, if the pots are otherwise identical and radiation
is the main difference, the black pot can lose heat faster.
The actual cooling rate also depends on the pot's material,
shape, surroundings and other modes of heat transfer.
5. Why are cloudy nights warmer than clear nights?
Answer:
Earth's surface emits infrared radiation after sunset.
Clouds absorb and emit some of this outgoing radiation back
towards the surface. This reduces the rate at which the
ground loses heat compared with many clear nights.
Therefore, cloudy nights are often warmer than clear nights,
although local weather conditions can change the outcome.
I. Thermos Flask: Concept-Based Question
Explain how a thermos flask minimises heat transfer.
Answer:
A thermos flask uses several features to reduce heat transfer.
- Vacuum between the walls: Reduces conduction and convection because very few particles are available to transfer energy across the gap.
- Silvered or reflective surfaces: Reduce heat transfer by thermal radiation.
- Insulating stopper: Reduces heat transfer through the opening.
- Insulating supports: Reduce conduction through the points where the inner container is supported.
J. Learning Beyond the Textbook
1. Identify the Modes of Heat Transfer
Question:
A metal pan containing water is placed over a flame.
Identify how heat is transferred:
- From the flame to the surroundings and pan.
- Through the metal pan.
- Within the water in the pan.
Answers:
- Radiation and convection from the flame and hot gases contribute to heating the pan.
- Conduction transfers heat through the metal pan.
- Convection currents transfer heat through the water, along with conduction.
2. Value-Based Question
Question:
Jyoti feels uncomfortable because smoke and hot air are
accumulating in Seema's kitchen. She suggests installing
a suitable ventilation system.
- How does ventilation help maintain air quality?
- What value does Jyoti demonstrate?
Answer:
Ventilation removes stale, warm or contaminated indoor air
and allows fresh outdoor air to enter. A properly designed
exhaust system can help remove smoke and cooking pollutants.
Jyoti demonstrates concern for others, helpfulness, awareness
of health and safety, and practical problem-solving.
3. Investigate: Temperature Scales
Question:
Take two bowls, one containing lukewarm water and the other
containing tap water. Measure their temperatures using a
suitable thermometer. Record each temperature in Celsius
and Fahrenheit.
Suggested observation table:
These are example readings, not actual measurements.
Use your own observations for the activity.
| Water sample | Temperature in °C | Temperature in °F |
|---|---|---|
| Lukewarm water | 40°C (example) | 104°F |
| Tap water | 25°C (example) | 77°F |
K. Final Revision Challenge
1. Which mode of heat transfer can take place through a vacuum?
Answer: Radiation.
Radiation does not require a material medium.
Radiation does not require a material medium.
2. Why are gaps left between railway tracks?
Answer:
The gaps allow the metal rails to expand in hot weather without excessive stress, bending or buckling.
The gaps allow the metal rails to expand in hot weather without excessive stress, bending or buckling.
3. Why does a hot-air balloon rise?
Answer:
Heating the air inside the balloon makes it less dense than the surrounding cooler air. The buoyant force can then lift the balloon.
Heating the air inside the balloon makes it less dense than the surrounding cooler air. The buoyant force can then lift the balloon.
4. What is thermal equilibrium?
Answer:
Thermal equilibrium is the state in which bodies in thermal contact have the same temperature and there is no net heat transfer between them.
Thermal equilibrium is the state in which bodies in thermal contact have the same temperature and there is no net heat transfer between them.
5. Why are shiny surfaces used inside a thermos flask?
Answer:
Shiny, reflective surfaces are poor emitters and absorbers of thermal radiation. They reduce heat transfer by radiation.
Shiny, reflective surfaces are poor emitters and absorbers of thermal radiation. They reduce heat transfer by radiation.
Well Done, Young Scientist!
You have completed the Heat chapter practice set. Before your examination, make sure you can explain the difference between heat and temperature, the three modes of heat transfer, thermal expansion, combustion, temperature conversions and the working of a thermos flask.
Remember:
Understanding the reason behind an answer is more valuable
than memorising the answer alone.
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