hot to cold - physics revision

Question 1

what is heat?

Answer 1

the energy stored within the particles on an object (J)

Question 2

what is temperature?

Answer 2

the effect of the energy on each particle (°C)

Question 3

what happens to the particles and temperature when energy is added?

Answer 3

• the temperature increases
• the particles move faster

Question 4

what happens to the particles and temperature when energy is taken away?

Answer 4

• the temperature decreases
• the particles move slower

Question 5

what happens to the temperature and particles when the energy is at equilibrium ( the amount of heat energy going in and out are equal)?

Answer 5

• the temperature stays the same
• the particles move at the same place

Question 6

what occurs in the A point in a cooling curve - with A being at the top, B being in the middle, and C being at the bottom

Answer 6

• the shape of a graph is a steep downwards curve
• the temp decreases quickly
• there is a large temperature difference between the object and the room

Question 7

what occurs in the B point in a cooling curve - with A being at the top, B being in the middle, and C being at the bottom

Answer 7

• the shape of a graph is a less steep downward curve
• the temperature decreases slightly slower
• there is a smaller temperature difference between the object and the room

Question 8

what occurs in the C point in a cooling curve - with A being at the top, B being in the middle, and C being at the bottom

Answer 8

• the graph is a plateau shape
• the temperature stays the same
• there is a no temperature difference between the object and the room

Question 9

what affects temperature?

Answer 9

• material (density)
• the mass
• the amount of energy given

Question 10

in the core practical ‘investigate how masterial affects temperature change’, what are the IV’s, DV’s, and CV’s

Answer 10

IV (change) - material
DV (material) - temperature change
CV (same) - mass, and amount of energy

Question 11

what happens to temperature with time?

Answer 11

it increases

Question 12

out of copper aluminium, brass, water and iron, which one would have the biggest temp change to smallest temp change?

Answer 12

copper, iron, brass, aluminium, water

each material has a different temperature rise for the same amount of energy supplied to the same mass

this means that for 1kg to rise by 1°C they need different amounts of energy - water needs the most energy

Question 13

what is specific heat capacity?

Answer 13

the amount of energy needed to raise the temperature of 1kg of a substance by 1°C

Question 14

what is the formula for specific heat capacity?

Answer 14

specific heat capacity = energy (J)
(J/kg/°C) —————————————
mass (kg) x temp change (°C)

energy = mass x SHC x temp change

temp change = energy
————-
mass x SHC

Question 15

what are the three ways of heat transfer?

Answer 15

• convection
• thermal radiation
• convection

Question 16

how does convection occur?

Answer 16

convection occurs in fluids (liquids in gases)
1. the radiator/ heat source heats the air
2. the air particles move apart, they have more kinetic energy - the air expands and becomes less dense. this then rises or floats
3. convection current
4. cooler air sinks as it’s more dense

Question 17

what is convection?

Answer 17

heat transfer in liquids and gases

Question 18

what is thermal radiation?

Answer 18

• thermal radiation occurs in a vacuum meaning no particles are needed
• it travels as a wave - like light
• also called infrared (IR)
• thermal energy radiates through space from the sun
• it is a form of heat transfer which is affected by colours

Question 19

how does thermal energy occur?

Answer 19

• when absorbing, the colour black attracts the most heat ( it gets hotter)
• when emitting, black also emits the most heat (loses the most heat)

Question 20

what are the IV’s DV’s and CV’s in the core practical ‘how good is insulation’, when a can of hot water is wrapped with insulation to see what the the temperature change is?

Answer 20

IV - the insulation
DV - change in temperature
CV - volume of water

Question 21

out of all the insulations, what would be the best?

Answer 21

thick and white cream foam - we know this because it had the smallest temperature change

it’s the best because it is a light colour (bad emitter of thermal radiation) it traps the heat in (bad at convection) and gases are trapped in the holes in the foam (bad at conduction)

Question 22

how does conduction occur?

Answer 22

• when heated particles move more they collide with other particles and pass the energy on
• particles in a solid are closer and regularly arranged so they conduct heat well. the free delocalised electrons take the energy through the solid quicker
• liquids and gases conduct poorly
• a vacuum doesn’t conduct as there aren’t any particles to pass the energy along to
• metals are the best conductors

Question 23

what is conduction?

Answer 23

conduction is a method of heat transfer that occurs in particles

Question 24

what is the best to worst conductor from aluminium, steel, brass and copper?

Answer 24

copper, aluminium, brass, steel

copper conducts the best because it has the most delocalised/free electrons

Question 25

what things are poor and good at conduction, convection and thermal radiation?

Answer 25

poor: conduction - gases convection - ? thermal radiation - light colours good: conduction - metals (solids) convection - free moving fluids thermal radiation - dark colours

Question 26

what is the units for energy in an energy bill?

Answer 26

since we use so much energy, an energy bill doesn't use joules, instead we use kWh - kilowatthour

Question 27

what is the equation for energy in an energy bill?

Answer 27

energy (kWh) = power (kW) x time (hours) time = energy ----------- power power = energy ----------- time