Thermal Energy

Question 1

Convection

Answer 1

• Part of a substance (liquid/gas) is heated.
• Particles in the substance gain KE and move around faster, making them spread out (the substance expands).
• This makes the substance less dense that the cooler substance.
• The hotter, less dense substance rises.
• Cooler denser substance replaces the hottie substance which has risen.
• Only happens in liquids and gases.

Question 2

Conduction

Answer 2

• A substance is heated up.
• Atoms are energised and vibration increases.
• Vibration is spread throughout the material - spreading the kinetic energy to the cooler parts by free electrons.

Question 3

What’s an example of a good heat conductor?

Answer 3

Metal

Question 4

Examples of conduction

Answer 4

Pan being heated on a stove

Question 5

Example of convection

Answer 5

Radiator - if you sit in a specific place, you will be able to feel coldness and warmth.

Question 6

Radiation

Answer 6

All objects emit and absorb (infra-red) radiation

Question 7

Are light shiny objects good or bad at absorbing and emitting thermal radiation?

Answer 7

Bad

Question 8

Loft insulation

Answer 8

• Conduction is reduced - air/glass are poor conductors.

* Convection is reduced - air is trapped in the fibre glass.

Question 9

Draught excluders

Answer 9

• Block the movement of air under doors.

* Reduces convection.

Question 10

Cavity wall insulation

Answer 10

• Breeze blocks come with foam - traps air (bad conductor).

* Trapped air won’t convect.

Question 11

Double glazing

Answer 11

• Radiarion can occur.
• Nearly a vacuum between the panes (metal strip) - no energy lost by conduction and convection.
• Very expensive.

Question 12

Carpets/Underlay

Answer 12

• Underlay is an extra layer of insulation.
• Reduces convection.
• Same principal as fibre glass - air trapped in between.
• Carpet is a bad conductor.

Question 13

What does the amount of radiation emitted depend on?

Answer 13

• The surface area of an object.
• The temperature difference between the object and the surroundings.
• The colour/texture of the surface.

Question 14

Example of radiation

Answer 14

Heat from the sun

Question 15

Why does conduction occur?

Answer 15

When a vibrating particle collides with other particles and passes the vibrations on.

Question 16

Why does convection occur?

Answer 16

When more energetic particles move from the hotter region to the cooler region and bring their heat energy with them.

Question 17

Why does radiation occur?

Answer 17

Objects that are hotter than their surroundings emit more radiation than they absorb as they cool down, and vice versa.

Question 18

Why does energy flow out of houses?

Answer 18

The inside of a house is warmer than the outside.