Heat — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Heat" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Heat" — 8 important questions with detailed answers for CBSE board exam preparation.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 7 Science — Heat. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Heat — All 8 Questions Solved
Q1. Define heat.
Heat is a form of energy that flows from a hotter body to a colder body.
It is measured in joules (J) or calories (cal).
1 calorie = 4.2 joules approximately.
Q2. What is the difference between heat and temperature?
Temperature is the measure of the degree of hotness of a body.
Heat is the energy transferred from one body to another due to temperature difference.
Temperature is measured in °C, °F or K; heat is measured in joules or calories.
Q3. A body is heated from 20°C to 50°C. Calculate the rise in temperature.
Rise in temperature = Final temperature - Initial temperature
= 50°C - 20°C
= 30°C
The rise in temperature is 30°C.
Q4. If 100 g of water is heated from 25°C to 75°C, calculate the heat energy required. (Specific heat capacity of water = 4200 J/kg°C)
Given: m = 100 g = 0.1 kg, T₁ = 25°C, T₂ = 75°C, c = 4200 J/kg°C
ΔT = 75 - 25 = 50°C
Q = m × c × ΔT
Q = 0.1 × 4200 × 50
Q = 21,000 J or 21 kJ
Q5. What is thermal expansion?
Thermal expansion is the increase in size of a substance when heated.
Most substances expand when heated and contract when cooled.
Different substances expand at different rates.
Q6. Define specific heat capacity.
Specific heat capacity is the amount of heat energy required to raise the temperature of 1 kg of a substance by 1°C.
Unit: J/kg°C
Different substances have different specific heat capacities.
Q7. How does heat travel through solids?
Heat travels through solids by conduction.
In this process, heat is transferred from one particle to adjacent particles without movement of the particles themselves.
Metals are good conductors of heat due to free electrons.
Q8. If 200 g of iron is heated from 30°C to 80°C, calculate heat required. (Specific heat capacity of iron = 450 J/kg°C)
Given: m = 200 g = 0.2 kg, T₁ = 30°C, T₂ = 80°C, c = 450 J/kg°C
ΔT = 80 - 30 = 50°C
Q = m × c × ΔT
Q = 0.2 × 450 × 50
Q = 4,500 J or 4.5 kJ
Heat — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Which of the following is the standard unit for measuring temperature?
- A. Joule
- B. Calorie
- C. Celsius
- D. Kilogram
Answer: C. Celsius — While Joule and Calorie measure heat energy, Celsius (and Fahrenheit, Kelvin) is a unit used to measure temperature, which indicates the degree of hotness or coldness of an object.
MCQ 2. A clinical thermometer is used to measure the temperature of:
- A. Boiling water
- B. The human body
- C. The atmosphere
- D. Industrial furnaces
Answer: B. The human body — Clinical thermometers are specifically designed to measure human body temperature and have a limited range, typically from 35°C to 42°C.
MCQ 3. The normal human body temperature is approximately:
- A. 98.6°C
- B. 37°C
- C. 0°C
- D. 100°C
Answer: B. 37°C — The normal human body temperature is approximately 37°C or 98.6°F. Options A, C, and D are incorrect for normal human body temperature.
MCQ 4. Heat from the sun reaches the Earth mainly by which mode of transfer?
- A. Conduction
- B. Convection
- C. Radiation
- D. Evaporation
Answer: C. Radiation — Radiation is the mode of heat transfer that does not require any medium. Heat from the sun travels through the vacuum of space to reach the Earth primarily through radiation.
MCQ 5. Which of the following is a good conductor of heat?
- A. Wood
- B. Plastic
- C. Iron
- D. Air
Answer: C. Iron — Good conductors allow heat to pass through them easily. Metals like iron, copper, and aluminum are good conductors, while wood, plastic, and air are insulators.
MCQ 6. Why does a clinical thermometer have a kink or a constriction near the bulb?
- A. To make it look attractive
- B. To prevent the mercury level from falling back on its own
- C. To allow the mercury to expand easily
- D. To make it easier to read the temperature
Answer: B. To prevent the mercury level from falling back on its own — The kink in a clinical thermometer prevents the mercury from falling back into the bulb immediately after being taken out of the patient's mouth, allowing time to read the temperature accurately.
MCQ 7. In which of the following substances is heat transferred mainly by convection?
- A. Solids
- B. Liquids
- C. Gases
- D. Both B and C
Answer: D. Both B and C — Convection is the mode of heat transfer that involves the actual movement of particles. This process occurs primarily in fluids, which include both liquids and gases.
MCQ 8. Why are the handles of cooking pans usually made of wood or plastic?
- A. They are cheaper materials
- B. They are good conductors of heat
- C. They are poor conductors of heat (insulators)
- D. They are lightweight
Answer: C. They are poor conductors of heat (insulators) — Wood and plastic are poor conductors of heat, also known as insulators. This prevents the heat from the pan from transferring to the hand, making it safe to hold.
MCQ 9. Which mode of heat transfer involves the movement of the medium itself?
- A. Conduction
- B. Convection
- C. Radiation
- D. Absorption
Answer: B. Convection — Convection is the process where heat is transferred by the actual movement of fluid (liquid or gas) particles from warmer regions to cooler regions.
MCQ 10. Sea breeze blows during the day because:
- A. Land heats up faster than the sea
- B. Sea heats up faster than the land
- C. Both land and sea heat up at the same rate
- D. There is no difference in heating rates
Answer: A. Land heats up faster than the sea — During the day, land heats up faster than the sea. The warm air above the land rises, and cooler air from the sea moves towards the land to take its place, creating a sea breeze.
MCQ 11. Which of the following thermometers has a much wider range, typically from -10°C to 110°C?
- A. Clinical thermometer
- B. Laboratory thermometer
- C. Digital thermometer
- D. Max-min thermometer
Answer: B. Laboratory thermometer — Laboratory thermometers are designed for general laboratory use and have a wide range, making them suitable for measuring temperatures of various substances other than the human body.
MCQ 12. We prefer to wear light-coloured clothes in summer because:
- A. They are fashionable
- B. They absorb more heat
- C. They reflect most of the heat
- D. They are made of thinner material
Answer: C. They reflect most of the heat — Light-coloured clothes reflect most of the heat radiation that falls on them, keeping our bodies cooler in hot weather. Dark-coloured clothes, conversely, absorb more heat.
MCQ 13. In which state of matter is heat generally transferred most efficiently by conduction?
- A. Solids
- B. Liquids
- C. Gases
- D. Plasma
Answer: A. Solids — Conduction is the primary mode of heat transfer in solids. The particles in solids are closely packed and vibrate, transferring energy to adjacent particles efficiently.
MCQ 14. If you touch a metal object and a wooden object at the same room temperature, the metal object feels colder. Why?
- A. Metal is naturally colder than wood
- B. Metal is a better conductor of heat than wood
- C. Wood has a higher specific heat capacity
- D. Metal reflects more cold from the environment
Answer: B. Metal is a better conductor of heat than wood — Metal feels colder because it is a better conductor of heat. It rapidly conducts heat away from your hand, making your hand lose heat faster and perceive it as colder, even though both are at the same temperature.
MCQ 15. A cooking pot is placed on a gas stove. Heat is transferred from the flame to the pot mainly by:
- A. Conduction
- B. Convection
- C. Radiation
- D. Evaporation
Answer: C. Radiation — Heat from the flame reaches the bottom surface of the pot primarily through radiation, which is the direct transfer of energy without a medium. Conduction and convection also occur with surrounding hot gases, but radiation from the luminous flame is a significant direct mode.
MCQ 16. What is the process by which heat flows from the hotter end to the colder end of an object without the actual movement of particles?
- A. Convection
- B. Radiation
- C. Conduction
- D. Evaporation
Answer: C. Conduction — Conduction is the transfer of heat through direct contact, where energy is passed from one particle to another within the material without the bulk movement of the material itself. This is characteristic of solids.
MCQ 17. Which material would you choose for the base of an electric iron, keeping in mind its function?
- A. Wood
- B. Plastic
- C. Aluminum
- D. Glass
Answer: C. Aluminum — An electric iron needs to transfer heat efficiently to clothes. Aluminum is a metal and an excellent conductor of heat, making it suitable for the base. Wood, plastic, and glass are insulators.
MCQ 18. Why do animals in very cold regions often have thick fur?
- A. Fur looks good
- B. Fur helps them camouflage
- C. Fur traps air, acting as an insulator
- D. Fur is a good conductor of heat
Answer: C. Fur traps air, acting as an insulator — Thick fur traps a layer of air close to the animal's body. Air is a poor conductor of heat (an insulator), which prevents body heat from escaping into the cold surroundings, thus keeping the animal warm.
MCQ 19. Which of these would be most effective in keeping a cold drink cool for a longer time on a hot day?
- A. A steel glass
- B. A plastic bottle
- C. A thermoflask
- D. An open glass filled with ice
Answer: C. A thermoflask — A thermoflask (or vacuum flask) is designed to minimize heat transfer by conduction, convection, and radiation, thus keeping its contents at their original temperature for extended periods.
MCQ 20. What happens to the level of mercury in a thermometer when it is placed in a hot liquid?
- A. It falls
- B. It rises
- C. It remains the same
- D. It solidifies
Answer: B. It rises — When a thermometer is placed in a hot liquid, the heat from the liquid causes the mercury in the bulb to expand. As mercury expands, its level rises in the capillary tube, indicating a higher temperature.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.