infrared, energy transfer by design snd specific heat capacity

Question 1

how does cooling by evaporation work

Answer 1

the molecules in the liquids have weak attractive forces

the faster the molecules (with more kinetic energy) break away from the attraction and excape the liquid

after they live the liquid is cooler because there is a lower average of kinetic energy in the remaining molecules

Question 2

what factors increase the rate of evaporation

Answer 2

1. increasing the liquids surface area
2. Increasing the liquids temperature
3. creating a draught of air across the liquids surface

Question 3

what factors increase the rate of condensation

Answer 3

1. increasing the surface area of a surface

2. reducing the temperature of a surface

Question 4

what factors affect the rate of energy transfer

Answer 4

1. the temperature difference between an objects and its surroundings
2. the shape, size and type of material the object comes in contact with
3. the materials the objects come in contact with

Question 5

what is cooling by evaporation work

Answer 5

using a liquid that evaporites easily and has a cooling sensation

Question 6

how fast is the temperature rise when an object with a high mass is heated

Answer 6

the greater the mass of an object the more slowly its tempreture increases when heated

Question 7

what does the rate of a temperature change depend on

Answer 7

1. the energy supplied to it
2. it’s mass
3. it’s specific heat capacity

Question 8

what do storage heaters use to store in special bricks

Answer 8

storage heaters use off- peak electricity to store energy in special bricks

bricks have high specific heat capacity (store lots of energy). they warm up slowly when heater element is in and cool down slowly when it’s off

Question 9

what is the specific heat capacity of a substance

Answer 9

the energy needed/ transferred to the 1kg of the substance to raise its tenpreture by 1*C

Question 10

what is the equation to work out the specific heat capacity

Answer 10

specific heat capacity (C) equals energy transferred (E) divided by mass (M) times tempreture change (ø)

Question 11

how can can energy transfer be reduced in our homes

Answer 11

by fitting:

1. loft insulation- in roof to reduce conduction
2. cavity wall insulation- pockets of air trapped between walls
3. double glazing- layer of air in between glass insulates
4. draught proofing

Question 12

what’s a U- value

Answer 12

the energy per second
that passes through one square metre of material
when the temperature difference across it is 1*C

Question 13

if a u value is low does that mean it’s an effective or not an effective insulator

Answer 13

the lower the u value the more effective the material is an a insulator

Question 14

what do solar panels do

Answer 14

heat water without using fuel

Solar hot water panels contain water pipes under a black surface radiation from the sun is absorbed by the black surface to heat the water in the pipes

connects to a heat exchanger in a water storage tank in the house

Question 15

what’s bad about solar panels

Answer 15

they are expensive to buy and install

unreliable

Question 16

if an object is hotter does it emit more or less infrared radiation

Answer 16

the hotter an object is the more infrared radiation it emits in a given time

Question 17

what’s the electromagnetic spectrum

Answer 17

1. set of radiations
2. that have different wavelengths and frequencies
3. all travel at the same speed in a vacuum

Question 18

what’s an electromagnetic wave

Answer 18

electric and magnetic waves that travel through space

eg infrared, visible light, microwaves, radio waves

Question 19

what does sun emit

Answer 19

electromagnetic radiation

but earths atmosphere doesn’t block infrared radiation because it has short wavelengths

Question 20

what does infrared and light from the sun do to the earth

Answer 20

warms it and is trapped

Question 21

what surfaces are the best emitters of radiation

Answer 21

dark, matt surfaces emit more infrared radiation than lightly shiny surfaces

Question 22

which surfaces are the best absorbers of radiation

Answer 22

dark matt surfaces absorb more infrared radiation than light, shiny surfaces

Question 23

what objects can emit/ absorb IR

Answer 23

any

whether or not conduction or covection are also taking place

Question 24

Where on a object is IR emitted from

Answer 24

IR is emitted from the surface of an object

Question 25

why do hot objects cool down and cold objects warm up

Answer 25

heat flows from the hotter object to the cooler

hotter object emits more radiation than absorbs so cools down

cold object absorbs more then it emits so it warms up

Question 26

what is the unit for specific heat capacity

Answer 26

j/kg*C

Question 27

how can you reduce convection

Answer 27

have something cool at the top of something hot so when the hot fluid rises it cools back down

a vacuum gap (reduces convection and conduction)

have the thing in a cupboard so warm air can’t escape

Question 28

why do radiators have a large surface area

Answer 28

to maximise amount of heat transfer

Question 29

what are things that Emit energy called

Answer 29

sources eh radiators

Question 30

what are things that transfer and waste energy called

Answer 30

sinks eg Windows

Question 31

why is water used to transfer heat around central heating systems

Answer 31

it has a high specific heat capacity and is easily pumped around pipes