P1: Heat Transfer

Question 0

If two objects of opposite temperature are put in contact with each other. What happens?

Answer 0

Heat energy will flow from the hotter to the colder object until they are in thermal equilibrium

Question 1

What is heat?

Answer 1

Energy that flows for on a hot region to cold region due to temperature differences between the two region.

Question 2

What are the processes where heat energy flows?

Answer 2

Conduction

Convection

Radiation

Question 3

What is conduction?

Answer 3

How heat energy flows from a hot to cold region of a substance without the molecules of the substance moving from the hot to cold region

Question 4

What is conduction by molecules?

Answer 4

Molecules vibrate more when they are heated
Intermolecular forces allow the molecules to pass their vibrations from one to another
The stronger the forces the faster the vibrations are passed
Solids are the best conductors and gases the worst
A poor conductor is called an insulator
A vacuum does not allow conduction

Question 5

What is conduction through metals?

Answer 5

Metals have an additional method of conduction.
Metals have electrons that can move from one atom to another
These free electrons can pass energy through the metal very quickly
Most of the best conductors are metals

Question 6

How can heat transfer by conduction be increased?

Answer 6

Better conducting substance

Decreasing thickness of substance

Increasing surface area of substance

Increasing temperature difference across the substance

Question 7

What is specific heat capacity?

Answer 7

The specific heat capacity of a substance is the amount of energy that is needed to raise the temperature of 1kg of the substance by 1°

Question 8

What is the specific heat capacity of water?

Answer 8

4200 J/Kg°C

Question 9

What is the unit of specific heat capacity?

Answer 9

J/Kg°C

Question 10

When there is a phase change what is happening to the molecules as heat is added?

Answer 10

It gives it a chance to stay vibrating at the same speed which means they can spread out and form the next state. Energy is being used to break bonds

Question 11

What is the process when a solid is going to a gas?

Answer 11

Vaporisation/Boiling

Question 12

What is the process when a solid changes directly into a vapour?

Answer 12

Sublimation

Question 13

Where does convection occur?

Answer 13

Liquid and gas

Question 14

What is convection?

Answer 14

When heat energy flows from a hot to cold region of a substance by molecules of the substance moving from the hot to cold region

Question 15

What happens when molecules are heated?

Answer 15

They move more quickly and occupy more space

Question 16

What are denser hotter or colder fluids?

Answer 16

Hotter fluids are less dense than colder fluids

Question 17

Which forms on top? Hotter or colder fluids?

Answer 17

Hotter

Question 18

What is a convection current?

Answer 18

The path taken by rising hot fluids and sinking cold fluids

Question 19

What is thermal radiation?

Answer 19

How heat energy moves from a hot to a cold region by means of electromagnetic waves

Question 20

What is thermal radiation also called?

Answer 20

Infra red or IR radiation

Question 21

Radiation travels far more quickly than the other forms of heat transfer. True or false?

Answer 21

True

Question 22

What is the only type of heat transfer thy can travel through a vacuum?

Answer 22

Radiation

Question 23

What allows radiation through best?

Answer 23

Gases are better than liquids, and liquids are better than solids.

Question 24

How can we detect thermal radiation?

Answer 24

Skin

Thermopile

Special cameras

Question 25

What objects give off thermal radiation?

Answer 25

All objects above absolute zero (-273°)

Question 26

The hotter an object gets, the more radiation it lets off. True or false?

Answer 26

True

Question 27

What are the best and worst emitters and absorbers of radiation?

Answer 27

Black rough surface
Black shiny surface
White rough surface
White shiny surface

Question 28

What are some uses of a silvered surfaces?

Answer 28

Kettle
Firefighter
Marathon runner

Question 29

What is evaporation?

Answer 29

The change of state from liquid to a gas, below the boiling temperature of the liquid

Question 30

Where is the heat energy taken from?

Answer 30

Surroundings

Question 31

Why does evaporation occur?

Answer 31

Because some molecules have more kinetic energy than others as if they are near the surface they can escape.

Question 32

How is the rate of evaporation increased?

Answer 32

Temperature is higher

Surface are is larger

Windy

Question 33

What is condensation?

Answer 33

Opposite of evaporation, a gas turns into a liquid. Heat energy is given to the surroundings. Hence condensation tends to occur on cold surfaces.

Question 34

What is the most effective and least effective heat lost preventions?

Answer 34

Draught excluder
Loft insulation
Cavity wall
Carpets
Double glazing

Question 35

What is payback time?

Answer 35

Pay back time is the time t takes you to get your money back. E.g. If loft insulation costs £400, but saves you £200 a year, the pay back time is 2 years

Question 36

What is a U-Value?

Answer 36

Determines the quality of an insulator. The lower the U-Value the better the insulator.

Question 37

What does a U-Value measure?

Answer 37

Rate at which heat energy is lost per metre squared for each degree temperature difference.

Question 38

How does a flask work?

Answer 38

It keeps hot things hot and cold things cold. It does this by stopping or reducing the transfer of heat by conduction, convections or radiation