Thermal Processes

Question 1

How is energy transferred by heating

Answer 1

Energy is transferred from a region of higher temperature to a region of lower temperature until both regions have the same temperature

Question 2

Define thermal equilibrium

Answer 2

A state in which two or more objects have same temperature and there is no net transfer of energy between them

Question 3

Define conduction

Answer 3

The transfer of heat through a medium without the physical movement of the medium

Question 4

Describe the process of conduction

Answer 4

Particles at the hotter end gain kinetic energy and vibrate more vigorously. Particles collide with neighbouring particles, transferring energy from one particle to another.
[For metals] metals have free moving electrons that move to cooler regions and transfer kinetic energy upon collisions with other particles

Question 5

Define convection

Answer 5

The transfer of heat from one place to another by physical movement of medium. Occurs in fluids by convection currents due to difference in density

Question 6

Describe heating of water in beaker by convection

Answer 6

Liquid near heat source gets heated, expands, becomes less dense and rises. Cooler, denser liquid at top sinks to take its place. This sets up convection current which heats up the whole liquid

Question 7

Describe cooling of air by air conditioner by convection

Answer 7

Air near air-con gets cooled, contracts, becomes denser and sinks. Warmer, less dense air at the bottom rises to take its place. This sets up convection current which cools down the whole room

Question 8

Define radiation

Answer 8

Transfer of heat in the form of infrared radiation without the need of a medium

Question 9

What are the factors affecting rate of emission and absorption of infrared radiation

Answer 9

Colour and texture of surface - dull/rough, black better than shiny/smooth white
Surface temperature - higher temp of surface of object relative to surrounding temp, higher rate of emission of radiation
Surface area - larger surface area -> greater rate

Question 10

What are answering techniques for “how is water in the bottle kept warm/cold” etc

Answer 10

• Identify feature - material/air spaces/trapped air/surface color or texture/surface area
• increases/decreases rate of heat gain/loss from __ to __ by *process
• State the reason (why feature helps)