SUMMARY
Thermal energy refers to the energy contained within a system that is responsible for its temperature.
Heat is a form of energy. Heat always flows from an object at higher temperature to an object at lower temperature.
Conduction is the transfer of heat through matter without the actual movement of particles from their positions.
Convection is the transfer of heat in which molecules of a medium actually move to the source of heat energy to absorb heat and then move away from it.
Radiation is the transfer of heat from a hot body to a cold body directly, without heating the space in between the two bodies.
Conduction occurs in solids, liquids and gases. But metals are better heat conductors.
Convection occurs only in liquids and gases.
Radiation needs no material medium to transfer heat energy.
Good and bad conductors of heat play very important role in our lives.
Convection causes wind and ocean currents.
Heat from the Sun reaches us by radiation.
Some birds take advantage of convection currents and glide in the air for hours.
A good radiator of heat is also a good absorber of heat.
A vacuum flask reduces the transfer of heat by conduction, convection and radiation to keep things hot or cold.
EVALUATION
What is thermal energy?
Illustrate that when two bodies are in contact, heat flows from the hot to the cold one.
Explain heat conduction and state its two applications.
Describe convection and list two of its applications.
Explain heat radiation and state two of its application.
Give short answers.
i. Why do we use cooking pots made of metals?
ii. What is a convection current?
iii. Which surfaces do absorb maximum heat?
iv. Why do we use woollen clothes and blankets during winter days?
v. What is the advantage of gliding flight for a bird?
Write a note on a vacuum flask.
Write brief notes on:
i. Ocean currents and winds
ii. Gliding flight of birds