NCERT Class 7 Science Chapter 7
Heat Transfer in Nature
This chapter explains the three modes of heat transfer — conduction, convection, and radiation — to CBSE Class 7 students with real-world examples. Students discover how heat moves through solids, liquids, and gases and understand natural phenomena such as sea breeze, land breeze, and the warming of Earth by the Sun. Practical experiments help students explore the concept of thermal conductivity.
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Key Terms
- Conduction
- The transfer of heat through a solid material by direct contact, from a region of higher temperature to a region of lower temperature, without the movement of the material itself.
- Convection
- The transfer of heat through fluids (liquids and gases) by the movement of the fluid itself, where warmer, less dense fluid rises and cooler, denser fluid sinks.
- Radiation
- The transfer of heat in the form of electromagnetic waves (infrared radiation) without any medium. The Sun heats the Earth through radiation.
- Conductor (Thermal)
- A material that allows heat to pass through it easily. Metals like copper and iron are good thermal conductors.
- Insulator (Thermal)
- A material that does not allow heat to pass through it easily. Wood, plastic, and air are poor conductors and act as thermal insulators.
- Convection Current
- The circular movement of a fluid caused by differences in temperature and density, responsible for phenomena like sea breeze, land breeze, and atmospheric circulation.
Frequently Asked Questions
What are the three modes of heat transfer in Class 7?▾
The three modes of heat transfer are conduction (through solids by direct contact), convection (through fluids by movement of the fluid), and radiation (through empty space or air in the form of electromagnetic waves).
How does conduction work? Give an example.▾
In conduction, heat passes through a material from particle to particle without the material itself moving. For example, when you hold one end of an iron rod and the other end is in a flame, the heat travels along the rod and you feel the warmth.
What causes sea breeze and land breeze?▾
Sea breeze occurs during the day when land heats up faster than the sea, causing air over land to rise. Cooler air from the sea moves in to replace it, creating a sea breeze. Land breeze occurs at night when the reverse happens — the sea is warmer, so air over the sea rises and cool air from land moves toward the sea.
Why do we use dark-coloured clothes in winter?▾
Dark colours absorb more heat radiation from the Sun than light colours, which reflect heat. Wearing dark clothes in winter helps the body stay warmer by absorbing more of the Sun's heat energy.
How does the Sun heat the Earth if there is no medium in space?▾
The Sun heats the Earth through radiation, which does not require any medium. Solar energy travels as electromagnetic waves (infrared radiation) across the vacuum of space and is absorbed by the Earth's surface and atmosphere.
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