Chapter 8: Transfer Of Themal Energy

Question 1

Flow of thermal energy

Answer 1

Thermal energy always flow from a region of higher temperature to a region of lower temperature

Question 2

Net flow

Answer 2

Net flow of thermal energy occurs when this is a difference in temperature

Question 3

How is thermal energy transferred?

Answer 3

1. Conduction
2. Convection
3. Radiation

Question 4

What is conduction?

Answer 4

The transfer of thermal energy through a medium without any flow of the medium

Question 5

How does conduction work? (Non-metals)

Answer 5

1. Particles at the heated end vibrate vigorously
2. They collide with neighbouring particles and transfer their energy
3. Eventually particles at the cooler end are set into vigorous vibration

Question 6

How does conduction work? (Metals)

Answer 6

OTW

Question 7

What is convection?

Answer 7

The transfer of thermal energy by means of convection currents in a fluid, due to a difference in density

Question 8

What is radiation?

Answer 8

The transfer of thermal energy in the form of electromagnetic waves such as infrared radiation without the aid of a medium

Question 9

Factors affecting the rate of emissions and absorption of infrared radiation

Answer 9

1. Colour and texture of the surface
2. Surface temperature
3. Surface area

Question 10

Colour and texture of the surface

Answer 10

Dull and black surface —> better emitters

Shiny and silver surface —> worser emitters

Question 11

Surface temperature

Answer 11

Higher temperature —> higher rate

Lower temperature —> lower rate

Question 12

Surface area

Answer 12

Larger surface area —> emit/absorb at a higher rate

Smaller surface area —> emit/absorb at a lower rate

Question 13

Differences between conduction, convection and radiation

Answer 13

CONDUCTION
Thermal energy is transferred from one particle to another
CONVECTION
Thermal energy is transferred through the actual movement of the heated particles from the warmer to cooler parts of the fluid
RADIATION
Do not require a medium for energy transfer

Question 14

Common applications of conduction

Answer 14

GOOD CONDUCTORS OF HEAT
1. Cooking utensils
2. Soldering iron rods
3. Heat exchanges
POOR CONDUCTORS OF HEAT (USES OF INSULATORS)

Question 15

What is free electron diffusion?

Answer 15

The process by which free electrons at the heated end of the metal rod gain thermal energy and moves to cooler regions

Question 16

Process of convection

Answer 16

1. The fluid near the heat source gets heated up
2. The part of the fluid at higher temperature expands, becomes less dense and rises
3. The surrounding fluid, being denser, sinks to replace the rising, hotter fluid
4. The movement of fluid sets up a convection current