Energy Transfers by Heating

Question 1

What can the thermal conductivity of an object tell you?

Answer 1

How quickly energy is transmitted through it by thermal conduction

Question 2

How can you test the thermal conductivity of rods of different metals?

Answer 2

• Each rod must have the same diameter and length
• Same temperature difference between its ends
• Place rods flat on a tripod
• One end of each rod covered in wax and the other ends heated equally using a bunsen burner
• The faster the wax melts, the higher the thermal conductivity of the metal

Question 3

Why is it important to reduce the rate of heat loss from a building?

Answer 3

Heating bills can be expensive

Question 4

What are 2 factors that can affect the rate of heat loss from a building?

Answer 4

• The thickness of its walls and roof
• The thermal conductivity of its walls and roof

Question 5

How can the thermal conductivity of the walls and roof be reduced?

Answer 5

By using thermal insulators

Question 6

What is a thermal insulator?

Answer 6

• A material that has a low thermal conductivity
• The rate of energy through an insulator is low

Question 7

What are 3 things that the energy transfer per second through a material depends on?

Answer 7

• The material’s thermal conductivity
• The temperature difference between the two sides of the material
• The thickness of the material

Question 8

What are 5 features that can be added to a house to reduce thermal conductivity?

Answer 8

• Loft insulation
• Cavity wall insulation
• Draught excluder
• Aluminium foil between a radiator panel and the wall
• Double-glazed window

Question 9

What does temperature change depend on when a substance is heated or cooled?

Answer 9

• The substance’s mass
• The type of material
• How much energy is transferred to it

Question 10

What is a material’s specific heat capacity?

Answer 10

The amount of energy needed to raise the temperature of 1kg of the substance by 1 degree celsius

Question 11

What is infrared radiation?

Answer 11

• Part of the electromagnetic system
• All objects emit (give out) and absorb (take in) infrared radiation
• The higher the temp, the more infrared it emits
• Good absorbers are also good emitters

Question 12

What is infrared radiation like for an object at a constant temperature?

Answer 12

• Infrared radiation emitted = infrared radiation absorbed
• Infrared radiation is emitted across a continuous range of wavelengths

Question 13

What happens to an object’s temperature when it absorbs infrared emission at a higher rate than it emits it?

Answer 13

It will increase

Question 14

What does the temperature of the Earth depend on?

Answer 14

Rate at which visible light and infrared radiation are:
- Reflected
- Absorbed
- Emitted
By the Earth’s atmosphere and surface

Question 15

What are examples of human activities that are increasing the amount of greenhouse gases in the Earth’s atmosphere?

Answer 15

• Burning fossil fuels
• Deforestation
• Livestock farming

Question 16

What do greenhouse gases do?

Answer 16

• Absorb infrared radiation emitted by the surface of the Earth and prevent it escaping into space
• They then re-emit the infrared radiation back towards the surface of the Earth, increasing the Earth’s temperature

Question 17

What are the greenhouse gases in the Earth’s atmosphere?

Answer 17

• Water vapour
• Carbon dioxide
• Methane

Question 18

What is a black body?

Answer 18

• A theoretical object that absorbs 100% of the radiation that falls on it
• A perfect black body would not reflect or transmit any radiation
• Would also be a perfect emitter of radiation

Question 19

How is radiation transmitted in the Earth’s atmosphere?

Answer 19

• Radiation from the Sun heats the Earth’s atmosphere
• Some radiation is emitted back into space
• Longer wavelength radiation emitted by the Earth’s surface is absorbed by greenhouse gases in the atmosphere
• Greenhouse gases re-emit radiation, increasing the temperature of the Earth