Energy transfer in the home

Question 1

What is condensation?

Answer 1

When a gas turns into a liquid

Question 2

What happens when a gas cools? (3)

Answer 2

The particles slow down
lose kinetic energy
The attractive forces between the particles pulls them closer together

Question 3

When can condensation take place? (2)

Answer 3

If the gas gets cool enough

If the particles get close enough together so that it becomes a liquid

Question 4

When does water vapour in the air condense?

Answer 4

When it comes into contact with a cold surface

Question 5

What is steam coming out of the kettle?

Answer 5

Invisible water vapour condensing into water droplets

Question 6

Evaporation is when?

Answer 6

A liquid turns into a gas, particles escape from a liquid

Question 7

When can particles near the surface of liquids evaporate?

What do the particles have to be doing to do this? (2)

Answer 7

At temperatures lower than its boiling point

1. Travelling in the right direction to escape the liquid
2. Travelling fast enough to overcome the attractive forces of the other particles in the liquid

Question 8

What happens when the particles with the most kinetic energy leave the liquid through evaporation? (2 steps)
Why is this effect useful?

Answer 8

The average speed or kinetic energy of the remaining particles decreases
so there is less energy in the liquid so the temperature of the liquid decreases
The cooling effect is useful which is why you sweat to cool you down

Question 9

The rate of evaporation will be faster if: (4)
Why? for each point…
P = particle

Answer 9

Temperature is higher - the average P energy will be higher so more P will have enough energy to escape
Density is lower - forces between P will be weaker so more P will have the energy to overcome the attraction and escape the liquid.
Surface area is larger - more P will be nearer to the surface to escape the liquid
Airflow over the liquid is greater - if there is a low concentration of the evaporating substance in the in the air then the rate of evap will be higher, a greater airflow means the air above the liquid will be replaced more often so the concentration will be lower.

Question 10

The rate of condensation will be faster if: (4)
Why? for each point…
P = particle

Answer 10

Temperature of the gas is lower - the average P energy will be lower so more P will slow down enough to clump into liquid droplets
Airflow is less - the concentration of substance in the air will be higher so the rate of condensation will be greater
Temp of the surface the gas touches is lower
Density is higher - the forces between the particles will be stronger so few particle swill have the energy to overcome these and instead will clump together

Question 11

What does the rate of heat and energy transfer depend upon? (3)

Answer 11

Surface area
Volume
Type of material

Question 12

Where is heat energy radiated form on an object?

Answer 12

its surface

Question 13

The bigger the surface area of an object …….. (to do with heat transfer)
so the quicker the ….

Answer 13

…. the more infrared waves can emitted from or absorbed by the surface, transfer of heat
….. transfer of heat

Question 14

Why do vehicle engines have fins?

Answer 14

To increase surface area so heat is radiated away quicker so the engine cools quicker

Question 15

What are heat sinks?

What do they have to do this?

Answer 15

Devices designed to transfer heat away from objects they’re in contact with quickly
Fins with large surface areas so they can emit heat quicly

Question 16

If two objects have the same temperature and the same surface area but different volumes:
the object with the smaller volume will…
because ….

Answer 16

… cool more quickly

…. a higher proportion of the object will be in contact with its surroundings

Question 17

Objects made from good …. transfer heat away more quickly than objects made from …… materials
It also matters if the object is in contact with an … or ….

Answer 17

conductors, insulating

insulator or conductor

Question 18

If an object is in contact with a conductor the heat will…

Answer 18

be conducted away much faster than if it is in contact with an insulator.

Question 19

Describe how a vacuum flask is designed to keep heat in and heat out: - link to energy transfer e.g radiation

1. The bottle:
2. The walls…… are ….
3. Bottle is supported with…
4. The stopper is made from …

Answer 19

1. is glass and double walled with a vacuum between the walls to stop all conduction and convection
2. either side of the vacuum are silvered to stop heat loss through radiation
3. Insulating foam to minimize heat loss (conduction) to or from the glass bottle from the plastic outside
4. Plastic filled with cork or foam to reduce any heat conduction through it.

Question 20

In the cold what happens to animals’ hairs and fur and why?

Answer 20

They stand on end to trap a thick layer of insulating air around the body limiting the amount of heat lost through convection

Question 21

Why does skin go pink when people get hot?

Answer 21

the body diverts more blood flow to the capillaries near the surface of the skin so more energy can be lost through heat radiation

Question 22

Why do some animals have larger or smaller ears?

Answer 22

In warm climates they have larger ears to give a large surface area for them to lose heat by radiation to keep cool, when they’re small in the cold to conserve heat lost through radiation