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Physics - P1 > P1.1 Transfer of energy > Flashcards

P1.1 Transfer of energy Flashcards

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1
Q

The bigger the temperature difference between a body and its surroundings…

A

, the faster the energy is transferred by heating. QA

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2
Q

5 key points about infrared radiation

A
  • ALL object emit + absorb IR
  • hotter the object- more IR it radiates in a given time
  • dark, matt surfaces- good absorbers + emitters of IR
  • light shiny surfaces- poor absorbers + emitters of IR
  • light shiny surfaces- good reflectors of IR
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3
Q

What are the 3 states of matter?

A

solid, liquid, gas

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4
Q

Describe the arrangement and energy of particles in solids

A
  • Strong forces of attraction hold the particles together in a fixed regular arrangement
  • Do not have much energy- vibrate around fixed positions
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5
Q

Describe the arrangement and energy of particles in liquids

A
  • weaker forces of attraction between particles.
  • Close together but can move past each other
  • irregular arrangement
  • more energy than particles in a solid
  • move in random directions at low speeds
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6
Q

Describe the arrangement and energy of particles in gasses

A
  • almost no forces of attraction between particles
  • have more energy than those in liquids and solids
  • free to move
  • travel in random directions at high speeds
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7
Q

What happens when you heat a substance?

A

particles have more kinetic energy .

vibrate or move faster

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8
Q

What is conduction of heat energy?

A

the process where vibrating particles pass on their extra kinetic energy to neighbouring particles

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9
Q

What is an insulator?

A

A material that has large spaces between it’s particles so conduct heat energy much slower.

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10
Q

Why are metals good conductors?

A

There are free electrons, which are free to move around the metal. - more collisions

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11
Q

What is a conductor?

A

A material that has smaller spaces between its particles (denser) - conduction is faster

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12
Q

Definition of convection

A

convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.

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13
Q

Why can’t convection happen in solids?

A

As the particles cant move

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14
Q

Describe convection in a hot water tank

A
  • heat energy transferred fro heat coils to water by conduction
  • particles near coils gain more energy- move faster
  • particles move apart so water expands + becomes less dense
  • hotter water rises above cooler water
  • as hot water rises it displaces the colder water, making it sink
  • process continues
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15
Q

Describe the process of condensation

A
  • when gas cools, particles slow down- kinetic energy of particles is reduced
  • Attractive forces between particles pull them closer together
  • if particles get close enough, condensation occurs
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16
Q

Describe the process of evaporation

A
  • liquid temperature increases- particles have more kinetic energy, move faster
  • becomes less dense
  • weaker attractive forces between particles
  • if hot enough, evaporation takes place
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17
Q

When does evaporation occur? (2 factors)

A
  • if particles are travelling in right direction to escape liquid
  • if particles are travelling fast enough (enough kinetic energy) to overcome attractive forces of other particles in liquid
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18
Q

Why does the temperature of the liquid in a container decrease as the liquid evaporates?

A

Particles with the most energy leave the surface of the liquid

So the average energy of the remaining particles goes down

and the lower the average energy of the particles the lower the temperature of the liquid

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19
Q

What increases the rate of evaporation? (4 factors)

A
  • Temperature is higher
  • Density is lower- as forces between particles will be weaker
  • surface area is larger- more particles will be near the surface to escape
  • Airflow over the liquid is greater- so lower concentration of evaporating substance in the air, so air above liquid is replaced more quickly
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20
Q

What increases the rate of condensation?

A
  • Temperature of gas is lower- lower kinetic energy
  • Temperature of surfaces gas touches is lower
  • Density is higher- forces between particles is stronger
  • Airflow is less- concentration of substances in air will be higher
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21
Q

what 4 factors increase the rate at which an object transfers energy by heating (cooling)

A
  • Larger surface area- more infrared waves can be emitted
  • Smaller volume- higher proportion of the object will be in contact with the surroundings
  • Conductors- metal (Material from which the object is made)
  • If object is in contact with a conductor (The nature of the surface with which the object is in contact )
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22
Q

Describe some adaptations humans and animals have to control the rate of heat transfer

A
  • Hairs on skin stand up when cold-traps a thicker layer of insulating air round body
  • Body diverts more blood to flow near surface of skin when hot - so more heat can be lost by radiation
  • Animals in warm environments have larger ears- large surface area to lose heat by radiation
  • Animals in cold environments have smaller ears- small surface area- minimise heat loss by radiation
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23
Q

Describe how a flask is designed to limit heat transfer

A
  • double-walled with a vacuum- stops all conduction and convection
  • walls are silvered- reduce heat loss by radiation
  • insulating foam- minimises heat conduction
24
Q

What do U-values measure?

A

how effective a material is as an insulator

25
Q

The lower the U-value….

A

the better the material is as an insulator

26
Q

How are solar panels used?

A

contain water that is heated by radiation from the sun

hot water may be used to heat buildings or to provide domestic hot water

27
Q

What is the specific heat capacity of a substance?

A

the amount of energy required to change the temperature of 1 kilogram of the substance by 1 degree celsius

28
Q

The equation for specific heat capacity is E=m x c x q

What do each of the letters stand for and what are they measured in?

A

E- energy transfer - joules J

m- mass- kilograms kg

q- temperature change- degrees celsius oC

c- specific heat capacity- J/kg oC

29
Q

What are some types of materials used for insulation?

A

CAVITY WALL INSULATION- foam squirted into a gap between brick- reduces convection and radiation across the gap.

LOFT INSULATION- thick layer of fibreglass wool laid out across the whole floor reduces conduction and radiation into roof space from ceiling

30
Q

Name some materials that have a high specific heat capacity

A

water, concrete, bricks, oil

31
Q

Why are oil heating systems not as good as water based systems?

A

as oil has a lower specific heat capacity than water

32
Q

Describe electric storage heaters

A

store heat energy at night (when electricity is cheeper) then release it during the day

they store heat using concrete or bricks- high specific heat capacity

33
Q

Describe why if a window is double glazed rather than single glazed, there is less condensation on the inside of the glass

A

as double glazing provides better insulation

therefore the inside of the glass is not as cold

34
Q

Explain the process of conduction through metals

A

metals have free electrons

the kinetic energy of free electrons increases when the metal is heated

this causes the free electrons to move faster and throughout the metal

free electrons collide with ions in the metal, transferring energy to them

35
Q

How does plastic foam reduce energy transfer by convection?

A

Air bubbles are trapped in the foam

and so the air can not circulate and form convection currents

36
Q

Why is a radiator painted black?

A

as black is a good emitter of infrared radiation

This gives the maximum rate of energy transferred to the surroundings

37
Q

Why do radiators have cooling thins?

A

As the fins increase the surface area, increasing the rate of energy transfer

38
Q

Why does one kilogram of gas have a much larger volume than one kilogram of solid?

A

There are strong forces of attraction between the particles in a solid

they hold the particles close together in a fixed position

but in a gas, the forces between the particles is very small

so the particles spread out

39
Q

Describe why a mirror gets misty when a person uses a shower

A

water evaporates producing water vapour

the mirror surface is cooler than the air

water molecules hit the mirror and lose energy

This causes the particles to move closer together which causes condensation on the mirror

40
Q

Why does a heated mirror not become misty if you have a shower?

A

as the mirror surface is warmer

so the rate of condensation is reduced

41
Q

Describe how a plastic cap on a flask helps to keep the liquid inside hot

A

plastic is an insulator

it stops convection currents forming at the top of the flask so stopping energy transfer by convection

also, particles evaporating from the hot liquid cannot move into the surrounding air so the cap stops energy transfer by evaporation

Also it reduces energy transfer by conduction

42
Q

Describe how the glass container in a flask keeps the liquid inside hot

A

glass is an insulator so reduces energy transfer by conduction

43
Q

Describe how the vacuum created in a flask helps to keep the liquid inside it hot

A

both conduction and convection require particles

so it stops energy transfer between the 2 walls by conduction and convection

44
Q

Describe how the silvered surface on the inside of the flask helps to keep the liquid inside it hot

A

silvered surfaces reflect infrared radiation so infrared radiation is partly reflected back towards the hot liquid

silvered surfaces are poor emitters of infrared radiation

they reduce energy transfer by radiation

45
Q

When there is a bigger temperature difference between water and the surrounding air….

A

the transfer of energy is faster

46
Q

Explain why fitting an insulating jacket to a hot water tank saves money

A

water stays hotter for longer

so heater is on for less time

so the cost of the jacket is soon recovered from the lower energy bills

47
Q

Explain why copper pipes inside solar panels are painted black?

A

because black is a good absorber of radiation

therefore there will be a faster transfer of energy

48
Q

Explain how an alcohol based hand gel makes your hands feel cold

A

to evaporate, the alcohol requires energy

this energy is taken away from the skin and the skin feels cold

49
Q

Explain why a liquid cools down when it evaporates

EXAM ANSWER- LEARN

A
  • there are attractive forces between molecules
  • only the fastest molecules have enough energy to break away from other molecules
  • these molecules escape from the surface of the liquid
  • therefore the average speed and energy of the remaining molecules goes down
  • the lower the average speed and energy of the molecules, the lower the temperature of the liquid
50
Q

How is the U-value affected by increasing the amount of insulation?

A

it decreases

51
Q

What is meant by the term ‘U-value’?

A

how EFFECTIVE a material is as an INSULATOR

52
Q

Why is it important that material X has a high specific heat capacity?

A

so it can store large amounts of energy

53
Q

What is specific heat capacity measured in?

A

J/Kg degrees

54
Q

Explain how energy is transferred though the metal walls of a can through conduction

A
  • in the metal there are free electrons
  • they gain kinetic energy
  • free electrons transfer energy to other electrons and ions
  • by collision
55
Q

Give 2 features that would help metal cooling fins to transfer energy quickly to the surroundings

A

large surface area

black

Physics - P1 (5 decks)

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