Unit 1A - Energy Flashcards
0
Q
Heat radiation is the transfer of heat energy through?
A
Infrared radiation
1
Q
What is the three different ways heat energy is transferred?
A
Radiation, conduction or convection
2
Q
Conduction and convection transfer heat energy by?
A
The movement of particles
3
Q
Which type of heat transfer can be emitted by solids, liquids and gases?
A
Radiation
4
Q
Conduction is the main form of heat transfer it which state of matter?
A
Solids
5
Q
What type of heat transfer happens in liquids and gases?
A
Convection
6
Q
What causes the energy to be transferred by heating faster?
A
Bigger temperature difference between two things
7
Q
All objects are continually emitting and absorbing what type of heat transfer?
A
Infrared radiation
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
9
Q
The more radiation it radiates in a given time is caused by?
A
The hotter the object is
10
Q
Amount of radiation depends on what two things a lot?
A
Surface colour and texture
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
12
Q
What type of surface reflect a lot of the infrared radiation that is falling on them?
A
Light, shiny surfaces
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
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
15
Q
What are the three states of matter?
A
Solid, liquid and gas
16
Q
What changes between each state of matter?
A
The arrangements and energy of the particles
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
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
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
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
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
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
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
24
Why makes metals good conductors?
Their free electrons
25
Why do free electrons make conduction happen faster?
The electrons can more freely and collide with other free electrons and so they can move and transfer the energy a lot faster
26
Is condition more effiecent through a short fat rod or a long thin rod and why?
Short fat rod because the electrons don't have to transfer energy as far as in a long rod
27
What is the definition of convection?
Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them
28
What three things use convection to heat things?
Immersion heaters in kettles, not water tanks and convector heaters
29
Why can't convection happen in solids?
Because the particles are unable to move to the different regions
30
How does an immersion heater work?
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
31
What is a convection current?
The change in density which causes the liquids to rise and then sink causing a current
32
Hat type of container are convection currents most efficient in?
Roundish or squarish because they allow the currents to work better
33
Other than an immersion heater what relies of convection currents too?
A radiator
34
What is condensation?
When gas turns to liquid
35
What happens to the particles during condensation?
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
36
What is evaporation?
When liquids turn into gases
37
What happens to particles during evaporation?
They're escape and leave the liquid
38
At what temperature can particles evaporate?
At room temperature much lower than the liquids boiling point
39
During evaporation what has to happen to the gas particles for them to escape?
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
40
What happens to the average particle energy during evaporation?
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
41
What four things cause the rate of evaporation to be faster and why?
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
42
What four things cause the rate of condensation to be faster and why?
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
Does the rate of heat transfer only depend on a few things?
No it depends on many
44
Why does a bigger surface are increase the rate if heat transfer?
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
Why do radiators have a large surface area?
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
Why do car and motorbike engines have fins?
Increase surface area so the heat is radiated away quicker, so the engine cools quicker
47
If two objects at the same temperature have the same surface area but different volumes which one would cool more quickly?
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
Other than surface area what affects the rate of heat transfer?
The type of material
49
If an object is made from a good conductor what is its effect of the rate of heat transfer?
They transfer heat away more quickly than insulating materials
50
How are vacuum flasks designed to reduce heat transfer?
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
How are humans designed to reduce heat loss and why?
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
How to animal ears help minimise or increase heat loss?
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
How do you figure out the payback time?
Initial cost / annual saving
54
Are effectiveness and cost effectiveness the same thing?
No they are different
55
What does a most effective methods of insulation mean?
They give you the biggest annual savings
56
What does a most cost effective method mean?
The cheapest methods that tend to have the shortest payback time
57
What is payback time?
How long it takes for the money you save each year to equal the initial cost of putting in the insulation
58
What is cavity wall insulation and how does it reduce heat loss?
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
What is loft insulation and how does it reduce heat loss?
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
What is draught proofing and how does it help to reduce heat loss?
Strips of foam and plastic around doors and windows to stop draughts , reduce the amount of convection
61
What is a hot water tank jacket and how does it reduce heat loss?
Fibreglass wool jacket across the hot water tank to reduce conduction and radiation from the tank
62
How do thick curtains reduce heat loss?
Reduce conduction and radiation
63
What is a u value?
They show how fast heat can transfer through a material
64
If heat transfers through materials fast does it have a high or low u value?
High
65
Does an insulator have a low or high u value and why?
Low because then it means heat can't transfer through to very fast
66
What does specific heat capacity tell you?
How much energy stuff can store
67
What is specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of a substance by 1c
68
What is waters specific heat capacity?
4200 J/kgc
69
What is the formula to figure out energy transferred in terms of specific heat capacity?
Energy transferred = mass x specific heat capacity x temperature change
70
Why do material used in heaters have to have high specific heat capacities?
So they can store large amounts of heat energy
71
How does an electric storage heater work?
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
Why is water good to use in central heating systems?
Really high specific heat capacity and it is a liquid and so can be pumped around in pipes
73
Some heaters use oil instead of water, what is an advantage of using oil?
It has a higher boiling point which means oil heated can safely reach higher temperatures than water based ones
74
What are the nine types of energy give and example for each?
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
What three energy types are forms of stored energy?
Gravitational potential, elastic potential and chemical energy
76
Can energy be created or destroyed?
No
77
What is the conversation of energy principal?
Energy can be transferred usefully from one form to another, stored or dissipated - but it can never be created or destroyed
78
What does dissipated mean?
Energy is spread out and lost
79
Other than the conservation of energy principle what is another important principle you have to know about the usefulness of energy?
Energy is only useful when it can be converted from one form to another
80
What are the energy transferred in an electrical device like a tv?
Electrical energy -----> light, sound and heat energy
81
Useful devices are only useful because they can do what to energy?
Transform energy from one form to another
82
Some of the useful input energy is always lost or wasted, often as what energy type?
Heat
83
What makes a more efficient device?
Less energy is wasted
84
How can you calculate efficiency of a device?
Efficiency = useful energy out / total energy in
85
If you don't know the energy inputs and outputs if a machine how else could you calculate the efficiency of a device?
By using the power input and out put
| Efficiency = useful power out / total power in
86
Why is no device 100% efficient?
No device is 100% efficient as there is wasted energy which is usually spread out as heat
87
What device is usually 100% efficient ?
Electrical heaters because all energy ends up as heat and so there would be no wasted energy
88
If the total amount of energy stays the same, why can't we use the wasted energy?
As it has become increasingly spread out, it can't be easily used or collected back in again
89
What do you need to think about when choosing new appliances?
How cost effective they are and the efficiency
90
To wrk out how cost effective a new appliance will be you need to work out its?
Payback time
91
Phone do heat exchangers reduce the amount of heat energy that is lost?
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
What is an example of a heat exchanger in a car?
Some of the wasted heat from the cars engine can be transferred to the air that's used to warm the passenger compartment
93
What is the name of an energy transfer diagram?
Sankey diagram
94
What do sankey diagrams show?
How much of the total energy I'm is being useful usefully transferred compared to how much is being wasted
95
In a sankey diagram what does a thicker arrow show?
The thicker the arrow the more energy it represents
96
What is useful energy, wasted energy and total energy in measured in?
Joules (J)
97
How can you calculate the amount of energy transferred in relation to power?
Energy = power x time
98
What is energy and power measured in?
Energy is measured in joules
| Power is measure in watts or kilowatts
99
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?
In kilowatts and hours instead of watts and seconds
100
What is the standard unit of electrical energy?
Kilowatt - hours
101
What is a kilowatt - hour ?
A kilowatt - hour is the amount of electrical energy used by 1kW appliance left on for 1 hour
102
How do you calculate the cost of electricity ?
Cost = no. Of units x price per unit
103
If you are given two meter readings how would you work out the total energy that had been used over a particular time period?
Subtract the meter reading at the start of the time from reading at the end of the time
104
When choosing electrical appliances what seek should you think about as well as efficiency and how cost effective it is?
Practical advantages and disadvantages like it can be used without being connected to the mains
105
Standard of living can be affected by?
Access to electricity
106
What things in a developed country does electricity make easier?
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
