Heat Transfer | Class 7 Science Notes
By ConceptScroll Team · Published on 17 July 2026 · 5 min read
Heat Transfer – this guide gives you a concise, exam-ready overview of Heat Transfer from Class 7 Science, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
7.2 Convection
Convection is the process of heat transfer through the actual movement of particles in liquids and gases. When a fluid (liquid or gas) is heated, it expands, becomes less dense, and rises, while the cooler, denser fluid sinks, creating a circulation pattern called a convection current. This section begins with an activity (Activity 7.2) using two paper cups suspended on a stick, where heating one cup causes it to rise due to the expansion and decrease in density of the air inside. The rising smoke from incense sticks and the expansion of air in a balloon heated by the Sun are everyday examples of convection. Another activity (Activity 7.3) demonstrates convection in water by adding potassium permanganate at the bottom of a beaker and heating it. The colored streak rises in the center and descends along the sides, showing convection currents. The section also explains land and sea breezes as natural phenomena caused by convection due to differential heating and cooling of land and water. During the day, land heats faster, causing warm air to rise and cooler air from the sea to move in (sea breeze). At night, land cools faster, causing cooler air to flow from land to sea (land breeze). These convection currents influence local weather and climate.
📊 Diagram: Figures 7.3a and 7.3b show two paper cups suspended on a stick, with a candle placed under one cup causing it to rise due to heated air expansion. Figures 7.5a and 7.5b depict a beaker with water and potassium permanganate at the bottom, showing colored streaks moving upwards and downwards due to convection currents.
🧪 Activity: Activity 7.2: Investigate convection by observing the movement of paper cups suspended on a stick when heated. Activity 7.3: Observe convection currents in water using potassium permanganate and heating.
🔗 Connection: Leads to the next section on radiation by explaining heat transfer in fluids and natural phenomena involving heat movement.
Frequently asked questions
1. Choose the correct option in each case. (i) Your father bought a saucepan made of two different materials, A and B, as shown in Fig. 7.14. The materials A and B have the following properties— (a) Both A and B are good conductors of heat (b) Both A and B are poor conductors of heat (c) A is a good conductor and B is a poor conductor of heat (d) A is a poor conductor and B is a good conductor of heat (ii) Pins are stuck to a metal strip with wax and a burning candle is kept below the rod, as shown in Fig. 7.15. Which of the following will happen? (a) All the pins will fall almost at the same time (b) Pins I and II will fall earlier than pins III and IV (c) Pins I and II will fall later than pins III and IV (d) Pins II and III will fall almost at the same time (iii) A smoke detector is a device that detects smoke and sounds an alarm. Suppose you are fitting a smoke detector in your room. The most suitable place for this device will be: (a) Near the floor (b) In the middle of a wall (c) On the ceiling (d) Anywhere in the room
1.(i) (c) A is a good conductor and B is a poor conductor of heat. Explanation: In a saucepan, the base (A) is usually made of a good conductor like metal to allow heat to pass quickly for cooking, while the handle (B) is made of a poor conductor (insulator) to prevent heat transfer and avoid burning the hand.
1.(ii) (b) Pins I and II will fall earlier than pins III and IV. Explanation: Pins closer to the heat source (pins I and II) will experience the melting of wax earlier due to conduction o
2. A shopkeeper serves you cold lassi in a tumbler. By chance, the tumbler had a small leak. You were given another tumbler by the shopkeeper to put the leaky tumbler in it. Will this arrangement help to keep the lassi cold for a longer time? Explain.
Yes, this arrangement will help keep the lassi cold for a longer time. Placing the leaky tumbler inside another tumbler reduces the direct exposure of the lassi to the external environment. The outer tumbler acts as an insulating layer, reducing heat transfer by conduction and convection from the surroundings to the lassi. This slows down the warming of the lassi, keeping it cold longer.
3. State with reason(s) whether the following statements are True [T] or False [F]. (i) Heat transfer takes place in solids through convection. [ ] (ii) Heat transfer through convection takes place by the actual movement of particles. [ ] (iii) Areas with clay materials allow more seepage of water than those with sandy materials. [ ] (iv) The movement of cooler air from land to sea is called land breeze. [ ]
(i) False. Heat transfer in solids mainly occurs through conduction, not convection.
(ii) True. Convection involves the actual movement of particles carrying heat.
(iii) False. Clay has very small pores and allows less seepage of water compared to sandy soil which has larger pores.
(iv) True. Land breeze is the movement of cooler air from land to sea, usually at night.
4. Some ice cubes placed in a dish melt into water after sometime. Where do the ice cubes get heat for this transformation?
The ice cubes get heat from the surrounding environment (air and the dish) which is at a temperature higher than the melting point of ice. Heat energy is transferred to the ice cubes by conduction and convection, causing them to melt into water.
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