Transfer Of Thermal Energy

Question 1

How is thermal energy transferred?

Answer 1

Thermal energy is transferred form a region of higher temperature to a region of lower temperature through conduction, convection and radiation

Question 2

What is conduction?

Answer 2

Conduction is the process by which thermal energy is transmitted through a medium from one particle to another

Question 3

How does conduction work?

Answer 3

1) when one end of a rod is heated, atoms there gain energy and vibrate faster
2) these atoms collide with their less energetic neighbors
3) some of their energy is transferred to these neighboring atoms, which in turn gain kinetic energy
4) in this way, energy is passed along the rod by vibrating atoms

Question 4

Conduction in liquids and gases

Answer 4

Solids are better conductors of thermal energy compared to liquids and gases

The molecules are closer together in solids allowing kinetic energy to be transferred more quickly

Question 5

What is convection?

Answer 5

Convection is the process by which thermal energy is transmitted from one place to another by the movement of gas or liquid

Question 6

Convection currents

Answer 6

When part of a liquid is heated, it expands in volume, becomes less dense than the surrounding liquid, and moves upwards

Cooler and denser liquid moved down to replace it. The cooler liquid in turn gets heated up and rises, resulting in a continuous convection current

Question 7

Convection in gases

Answer 7

Convection occurs much more readily in gases because gases expand much more quickly than liquids when their temperature rises

Question 8

How air conditioners work

Answer 8

Air conditioners should be positioned nearer to the ceiling of the room. Cold air sinks as it is denser than the warm air

Warm air in turn rises when it is displaced by the cold air and is drawn into the air conditioner

Question 9

What is radiation?

Answer 9

Radiation is the process by which thermal energy is transferred by electromagnetic waves

Question 10

Infra red radiation

Answer 10

From the sun, travels in the form of electromagnetic waves

When absorbed, infra-red radiation transforms into thermal energy of the receiving body

All objects emit infra-red radiation, and all objects absorb it

Question 11

Factors affecting emission of infra-red radiation

Answer 11

Surface temperature (hotter faster) 
Surface colour (darker) and texture (rougher) 
Surface area (larger)

Question 12

Absorption of infra-red radiation

Answer 12

A good emitter is also a good absorber of infra-red radiation

On the other hand, a shiny surface is a good reflector of infra-red radiation