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Physics > Unit 1A - Energy > Flashcards

Unit 1A - Energy Flashcards

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0
Q

Heat radiation is the transfer of heat energy through?

A

Infrared radiation

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1
Q

What is the three different ways heat energy is transferred?

A

Radiation, conduction or convection

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2
Q

Conduction and convection transfer heat energy by?

A

The movement of particles

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3
Q

Which type of heat transfer can be emitted by solids, liquids and gases?

A

Radiation

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4
Q

Conduction is the main form of heat transfer it which state of matter?

A

Solids

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5
Q

What type of heat transfer happens in liquids and gases?

A

Convection

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6
Q

What causes the energy to be transferred by heating faster?

A

Bigger temperature difference between two things

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7
Q

All objects are continually emitting and absorbing what type of heat transfer?

A

Infrared radiation

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8
Q

If an object is hotter or cooler than it’s surrounding what happens to the amount of radiation?

A

Hotter - emits more radiation than it absorbs as it cools down
Cooler - absorbs more radiation than it emits as it warms up

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9
Q

The more radiation it radiates in a given time is caused by?

A

The hotter the object is

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10
Q

Amount of radiation depends on what two things a lot?

A

Surface colour and texture

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11
Q

How do dark matt surfaces effect the amount of radiation?

A

Absorbs infrared radiation falling on them much better and emit much more infrared radiation

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12
Q

What type of surface reflect a lot of the infrared radiation that is falling on them?

A

Light, shiny surfaces

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13
Q

Why do vacuum flasks have silver inner surfaces?

A

Light shiny surfaces reflect a lot of infrared radiation falling onto them and so it keeps the heat in or out depending on whether it is storing hot or cold liquid

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14
Q

Why do solar hot water panels contain water pipes under a black matt surface?

A

Dark matt surfaces absorb infrared radiation falling on them and so this radiation from the sun is absorbed and is used to heat the water in the pipes, the heated water can be washing for washing or pumped to radiators

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15
Q

What are the three states of matter?

A

Solid, liquid and gas

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16
Q

What changes between each state of matter?

A

The arrangements and energy of the particles

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17
Q

What is the arrangements and energy of the particles in a solid?

A

Strong forces of attraction hold the particles close together in a fixed regular arrangement, as the particles don’t have much energy they can only vibrate about their fixed positions

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18
Q

What is the arrangements and energy of the particles in a liquid?

A

Weaker forces of attraction between the particles and so although the particles are close together they can move past each other and from irregular arrangements, they have more energy and so they more in random directions at low speeds

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19
Q

What is the arrangements and energy of the particles in a gas?

A

Almost no forces of attraction between particles, the particles have more energy than in a liquid or solid and so are free to move in random directions and at high speeds

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20
Q

What happens to the particles when you heat a substance?

A

The particles get more kinetic energy and so vibrate or move faster

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21
Q

What is the definition of conduction?

A

Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles

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22
Q

Why does conduction happen faster in denser solids?

A

The particles are close together and so will collide more often and pass energy between them

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23
Q

Why do insulators slow down the rate of conduction?

A

They have larger spaces between the particles and so so they can pass on the energy much slower

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24
Q

Why makes metals good conductors?

A

Their free electrons

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25
Q

Why do free electrons make conduction happen faster?

A

The electrons can more freely and collide with other free electrons and so they can move and transfer the energy a lot faster

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26
Q

Is condition more effiecent through a short fat rod or a long thin rod and why?

A

Short fat rod because the electrons don’t have to transfer energy as far as in a long rod

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27
Q

What is the 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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28
Q

What three things use convection to heat things?

A

Immersion heaters in kettles, not water tanks and convector heaters

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29
Q

Why can’t convection happen in solids?

A

Because the particles are unable to move to the different regions

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30
Q

How does an immersion heater work?

A

Heat energy is transferred from the heater coils to the water through conduction, particles near coil get more energy and move faster, this means there is more distance between the particles and so the water becomes less dense, the hotter water rises, says it rises it displaces the color water making that sink towards the heater coils, the cold water is then heated and rises and this goes on

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31
Q

What is a convection current?

A

The change in density which causes the liquids to rise and then sink causing a current

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32
Q

Hat type of container are convection currents most efficient in?

A

Roundish or squarish because they allow the currents to work better

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33
Q

Other than an immersion heater what relies of convection currents too?

A

A radiator

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34
Q

What is condensation?

A

When gas turns to liquid

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35
Q

What happens to the particles during condensation?

A

When a gas cools the particles slow down and lose kinetic energy, the attractive forces between the particles pull them close together, when the particles become close enough together then condensation takes places and the gas becomes a liquid

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36
Q

What is evaporation?

A

When liquids turn into gases

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37
Q

What happens to particles during evaporation?

A

They’re escape and leave the liquid

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38
Q

At what temperature can particles evaporate?

A

At room temperature much lower than the liquids boiling point

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39
Q

During evaporation what has to happen to the gas particles for them to escape?

A

The particles have to be travelling at the right direction to escape the liquid, and they have to be travelling fast enough ( have enough kinetic energy ) to overcome the attractive forces of the liquid

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40
Q

What happens to the average particle energy during evaporation?

A

The fastest particles with the most kinetic energy evaporate and so the average speed and kinetic energy of the remaining particles decreases, this causes the temperature to fall and the liquid to cool

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41
Q

What four things cause the rate of evaporation to be faster and why?

A

Higher temperature so particles have more energy
Lower density so the forces between the particles are weaker meaning more particles have enough energy to overcome these forces
Larger surface area so more particles will be close enough to the surface to evaporate
Greater airflow over the liquid so the concentration of the evaporated substance in the air is less increasing rate of evaporation

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42
Q

What four things cause the rate of condensation to be faster and why?

A

Lower temperature so the particles have less enough and are slower
Temperature of the surface the gas touches is lower
Density is higher so the forces of attraction will be stronger, fewer particles have enough energy to overcome these forces
Airflow is less so the concentration of the substance in the air will be higher and so the rate if condensation will be greater

43
Q

Does the rate of heat transfer only depend on a few things?

A

No it depends on many

44
Q

Why does a bigger surface are increase the rate if heat transfer?

A

The bugger the surface area, the more infrared waves that can be emitted from or absorbed by the surface so the quicker the transfer of heat

45
Q

Why do radiators have a large surface area?

A

Because a larger surface area increases the rate of heat transfer and so the larger surface area maximises the amount if heat it transfers

46
Q

Why do car and motorbike engines have fins?

A

Increase surface area so the heat is radiated away quicker, so the engine cools quicker

47
Q

If two objects at the same temperature have the same surface area but different volumes which one would cool more quickly?

A

The one with a smaller volume because a higher proportion of the inject is in contact with its surroundings and so it could more quickly

48
Q

Other than surface area what affects the rate of heat transfer?

A

The type of material

49
Q

If an object is made from a good conductor what is its effect of the rate of heat transfer?

A

They transfer heat away more quickly than insulating materials

50
Q

How are vacuum flasks designed to reduce heat transfer?

A

Doubled walled with a vacuum between the two walls which stops all conduction and convection through the sides as there is no particles , the walls are silvered to keep heat loss by radiation to a minimum and the stopper is made of plastic and filled witch rock or foam to reduce conduction through it

51
Q

How are humans designed to reduce heat loss and why?

A

Hairs on the skin stand up to trap a thick layer of insulating air around the body, reducing convection and when your hot the body diverts more blood to the surface to lose heat through radiation

52
Q

How to animal ears help minimise or increase heat loss?

A

Small ears mean a smaller surface area an so minimise heat loss by radiation
Big ears mean a larger surface area allowing them to lose heat through radiation

53
Q

How do you figure out the payback time?

A

Initial cost / annual saving

54
Q

Are effectiveness and cost effectiveness the same thing?

A

No they are different

55
Q

What does a most effective methods of insulation mean?

A

They give you the biggest annual savings

56
Q

What does a most cost effective method mean?

A

The cheapest methods that tend to have the shortest payback time

57
Q

What is payback time?

A

How long it takes for the money you save each year to equal the initial cost of putting in the insulation

58
Q

What is cavity wall insulation and how does it reduce heat loss?

A

Foam squirted into the gaps between bricks to stop convection currents being set up in the gap, reduced radiation across the gap and the insulating foam helps reduce conduction

59
Q

What is loft insulation and how does it reduce heat loss?

A

A thick layer of fibreglass will laid our across the whole loft floor, reduces conduction and radiation into the roof space from the ceiling

60
Q

What is draught proofing and how does it help to reduce heat loss?

A

Strips of foam and plastic around doors and windows to stop draughts , reduce the amount of convection

61
Q

What is a hot water tank jacket and how does it reduce heat loss?

A

Fibreglass wool jacket across the hot water tank to reduce conduction and radiation from the tank

62
Q

How do thick curtains reduce heat loss?

A

Reduce conduction and radiation

63
Q

What is a u value?

A

They show how fast heat can transfer through a material

64
Q

If heat transfers through materials fast does it have a high or low u value?

A

High

65
Q

Does an insulator have a low or high u value and why?

A

Low because then it means heat can’t transfer through to very fast

66
Q

What does specific heat capacity tell you?

A

How much energy stuff can store

67
Q

What is specific heat capacity?

A

The amount of energy needed to raise the temperature of 1kg of a substance by 1c

68
Q

What is waters specific heat capacity?

A

4200 J/kgc

69
Q

What is the formula to figure out energy transferred in terms of specific heat capacity?

A

Energy transferred = mass x specific heat capacity x temperature change

70
Q

Why do material used in heaters have to have high specific heat capacities?

A

So they can store large amounts of heat energy

71
Q

How does an electric storage heater work?

A

They are designed to store heat energy at night when electricity is cheaper and then release it during the day, they store the heat in conveyed or breaks as they have quiet a high specific heat capacity

72
Q

Why is water good to use in central heating systems?

A

Really high specific heat capacity and it is a liquid and so can be pumped around in pipes

73
Q

Some heaters use oil instead of water, what is an advantage of using oil?

A

It has a higher boiling point which means oil heated can safely reach higher temperatures than water based ones

74
Q

What are the nine types of energy give and example for each?

A
  1. ) electrical energy - whenever a current flows
  2. ) light energy - from the sun or light bulbs
  3. ) sound energy - from a loudspeaker
  4. ) kinetic energy - anything that is moving
  5. ) nuclear energy - released from nuclear reactions
  6. ) heat energy - wasted by light bulbs, flows from hot objects to colder ones
  7. ) gravitational potential energy - possessed by anything that can fall
  8. ) elastic potential - stretched springs, elastic bands
  9. ) chemical energy - in a battery
75
Q

What three energy types are forms of stored energy?

A

Gravitational potential, elastic potential and chemical energy

76
Q

Can energy be created or destroyed?

A

No

77
Q

What is the conversation of energy principal?

A

Energy can be transferred usefully from one form to another, stored or dissipated - but it can never be created or destroyed

78
Q

What does dissipated mean?

A

Energy is spread out and lost

79
Q

Other than the conservation of energy principle what is another important principle you have to know about the usefulness of energy?

A

Energy is only useful when it can be converted from one form to another

80
Q

What are the energy transferred in an electrical device like a tv?

A

Electrical energy —–> light, sound and heat energy

81
Q

Useful devices are only useful because they can do what to energy?

A

Transform energy from one form to another

82
Q

Some of the useful input energy is always lost or wasted, often as what energy type?

A

Heat

83
Q

What makes a more efficient device?

A

Less energy is wasted

84
Q

How can you calculate efficiency of a device?

A

Efficiency = useful energy out / total energy in

85
Q

If you don’t know the energy inputs and outputs if a machine how else could you calculate the efficiency of a device?

A

By using the power input and out put

Efficiency = useful power out / total power in

86
Q

Why is no device 100% efficient?

A

No device is 100% efficient as there is wasted energy which is usually spread out as heat

87
Q

What device is usually 100% efficient ?

A

Electrical heaters because all energy ends up as heat and so there would be no wasted energy

88
Q

If the total amount of energy stays the same, why can’t we use the wasted energy?

A

As it has become increasingly spread out, it can’t be easily used or collected back in again

89
Q

What do you need to think about when choosing new appliances?

A

How cost effective they are and the efficiency

90
Q

To wrk out how cost effective a new appliance will be you need to work out its?

A

Payback time

91
Q

Phone do heat exchangers reduce the amount of heat energy that is lost?

A

They pump a cool fluid through the escaping heat, the temperature of the fluid rises as it gains heat energy, the heat energy from the fluid can be converted into a form of energy that is useful again

92
Q

What is an example of a heat exchanger in a car?

A

Some of the wasted heat from the cars engine can be transferred to the air that’s used to warm the passenger compartment

93
Q

What is the name of an energy transfer diagram?

A

Sankey diagram

94
Q

What do sankey diagrams show?

A

How much of the total energy I’m is being useful usefully transferred compared to how much is being wasted

95
Q

In a sankey diagram what does a thicker arrow show?

A

The thicker the arrow the more energy it represents

96
Q

What is useful energy, wasted energy and total energy in measured in?

A

Joules (J)

97
Q

How can you calculate the amount of energy transferred in relation to power?

A

Energy = power x time

98
Q

What is energy and power measured in?

A

Energy is measured in joules

Power is measure in watts or kilowatts

99
Q

When you’re dealing with large amounts of electrical energy what is it easier to think of power and time as and instead of what?

A

In kilowatts and hours instead of watts and seconds

100
Q

What is the standard unit of electrical energy?

A

Kilowatt - hours

101
Q

What is a kilowatt - hour ?

A

A kilowatt - hour is the amount of electrical energy used by 1kW appliance left on for 1 hour

102
Q

How do you calculate the cost of electricity ?

A

Cost = no. Of units x price per unit

103
Q

If you are given two meter readings how would you work out the total energy that had been used over a particular time period?

A

Subtract the meter reading at the start of the time from reading at the end of the time

104
Q

When choosing electrical appliances what seek should you think about as well as efficiency and how cost effective it is?

A

Practical advantages and disadvantages like it can be used without being connected to the mains

105
Q

Standard of living can be affected by?

A

Access to electricity

106
Q

What things in a developed country does electricity make easier?

A

Electrical lighting, more convenient, improve safety at night
Refrigerators keep food death for longer by slowing down the growth of bacteria, they are also used to keep vaccines cold
Improving public health, hospitals use it for many things to diagnose and treat patients
We use it to communication with other people

Physics (7 decks)

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