Transfer of Thermal Energy

Question 1

Conduction

Answer 1

The transfer of thermal energy from a region of higher temperature to a region of lower temperature through molecular vibration/ free election diffusion (in metals).

Question 2

Molecular Vibration

Answer 2

Molecules at the hot end vibrate vigorously, colliding with their neighbouring molecules, making them vibrate as well.

Question 3

Free-electron diffusion

Answer 3

Free electrons at the hot end move faster as a result of having more kinetic energy, moving quickly to the cooler part of the material, and transferring their energy to other molecules by colliding with them.

Question 4

Convection

Answer 4

The transfer of thermal energy by the bulk movement of the fluid, due to convection current formed by density differences.

Question 5

Application of convection

Answer 5

1. Installation of air conditioner near to the ceiling.
2. Placement of heating elements at the bottom of kettles
3. Sea breeze during the day and land breeze during the night

Question 6

Radiation

Answer 6

The transfer of thermal energy from hot to cold regions by means of electromagnetic waves (infra-red radiation), without the need of a medium.

Question 7

Factors affecting radiation

Answer 7

1) Colour and texture of surface:
Dull, black surfaces are better heat emitters/absorbers of infra-red radiation, Shiny, white surfaces are poorer heat emitters/absorbers of infra-red radiation.
2) Surface temperature:
The higher the surface temperature, the greater the amount of heat transfer will take place.
3) Surface area:
The larger the surface area, the larger the area to emit heat, so the higher the rate of radiation