Heat

Question 0

Definition of Infra Red Radiation.

Answer 0

All objects give out infra red radiation. The hotter they are; the more they emit.

Question 1

Name the properties of a solid, liquid and gas.

Answer 1

Solid:
Density - Dense because the particles are tightly packed.
Shape - Keeps it’s shape because particles have strong bonds.
Flows - No

Liquid:
Dense - Quite dense because the particles aren’t as tightly packed.
Shape - Takes the shape of the bottom of a container because the particles have weak bonds.
Flows - Yes because the particles have weak bonds.

Gas:
Density - Low density because particles are for apart.
Shape - Takes the shape of the container because the particles have no forces.
Flow - Yes because the particles have no forces.

Question 2

What surfaces are best and worse at emitting IR?

Answer 2

Black matt surfaces emit radiation better than white shiny ones.

Question 3

Definition of conduction.

Answer 3

Conduction occurs mostly in solids (the particles need to be close to each other). Particles vibrate more when they are heated, and pass this energy to neighbouring particles. In a metal, free electrons can travel to other atoms and help transfer heat energy even quicker.

Question 4

Definition of convection.

Answer 4

Convection is all about when a gas or liquid (“fluid”) moves and carries heat with it. When a fluid is heated it expands. This means that it will become less dense than the colder fluid around it. Because of this the warmer fluid will try to “float” over the colder fluid, and this is why warm air or water rises. This is called a convection current.

Question 5

How does the heat from the Sun get to the Earth?

Answer 5

Conduction an convection need a medium. Radiation can pass through a vacuum. That’s how IR gets from the Sun to the Earth.

Question 6

What can you do to keep your house cool and explain why it works?

Answer 6

Paint the house white because white is poor at absorbing IR so the house stays cooler.

Question 7

Explain why it is not so bad to leave the lid off a chest freezer.

Answer 7

Cold air is more dense so it stays in the freezer.

Question 8

How does the plastic lid, vacuum between the glass walls and shiny walls help keep the contents of a vacuum flask hot/cold?

Answer 8

Plastic lid - reduces conduction because plastic is a thermal insulator.
Vacuum between glass walls - convection and conduction cannot take place in a vacuum so less heat transfers by these methods.
Shiny walls - Less IR is emitted from the inner layer because silver is a poor emitter. Also IR is reflected back from the other layer.

Question 9

What factors affect evaporation?

Answer 9

Surface area of water
Temperature of air and water
A breeze (air speed)

Question 10

What is temperature?

Answer 10

How hot something is (measured in oC)

Question 11

What is heat?

Answer 11

The thermal energy in an object (in Joules)

Question 12

What is the specific heat capacity?

Answer 12

Tells us how much heat energy is needed to increase the temperature by 1oC.

Question 13

Specific heat capacity formula.

Answer 13

E=mxcx0

Mass (m)
Energy (E)
Temp. change (0)
SHC (c)

Question 14

What is insulation?

Answer 14

Anything which reduces the heat energy transferred to the surroundings.

Question 15

What are the different types of energy?

Answer 15

Heat energy
Kinetic energy
Gravitational potential energy
Elastic potential energy
Sound energy
Electrical energy
Light energy
Chemical energy

Question 16

What does power mean?

Answer 16

How much energy is transferred (or used) every second.

Question 17

How do you work out power?

Answer 17

P=E/t
P is power
E is energy transferred
t is time taken to transfer

Question 18

How do you work out efficiency?

Answer 18

Useful energy divided by total energy

Question 19

How do you work out how much power something uses?

Answer 19

Power(kW)xtime(hrs)=energy use(kWh)