Heat Energy Transfer

Question 1

What materials are good at absorbing Infrared Radiation?

Answer 1

Dark, Matt surfaces

Question 2

What surfaces are poor emitters of Infrared radiation?

Answer 2

Light, Shiny surfaces

Question 3

How do radiators primarily transfer thermal energy to a room?

Answer 3

Through Convection.

(Even though they are called radiators…)

Question 4

Why would a wooden block feel warmer than a metal block when they are both at the same temperature?

Answer 4

Metals are better conductors.

Question 5

What factors affect the rate at which an object transfers thermal energy?

Answer 5

• The surface area
• The material of the object
• What the object is in contact with

Question 6

The lower the U-Value the…

Answer 6

better the material is as an insulator.

Question 7

Why do a vacuum flasks have a vacuum?

Answer 7

To stop heat lose through conduction and convection (but not IR).

Question 8

The silver metal object is a heat sink for a computer. It is fitted to help keep the computers components at a low temperature.

• Why does it have ‘fins’?
• Why is it made from a metal?

Answer 8

• So that it has a large surface area (to increase heat transfer)
• Metals are good conductors

Question 9

Why are metals good conductors of thermal energy?

Answer 9

They have free (delocalised) electrons.

Question 10

Explain how can all the air in a fridge be cooled if the unit only cools air at the top of the fridge.

Answer 10

• When the air at the top is cooled down it become more dense.
• The cool air sinks, allowing the wamer air to rise
• The warm air is then cooled
• This allows all the air in the fridge to be cooled

Question 11

How is thermal energy transferred from the sun to earth?Infererd radiation

Why can it only be transferred through that one type of energy transfer?

Answer 11

Inferred radiation.

Conduction and convetion require a medium (particles) but IR does not as it is a EM Wave.