Energy Flashcards
(137 cards)
1
Q
What are the units for energy?
A
Joules (J)
2
Q
What are the units for distance?
A
Metres (m)
3
Q
What type of energy is stored in a cell?
A
Chemical
4
Q
What is the law of conservation of energy?
A
Energy cannot be created or destroyed
5
Q
What can energy only ever be?
A
Transferred between different forms and objects
6
Q
What are the 8 energy stores?
A
Chemical
Kinetic
Gravitational potential
Elastic
Thermal
Magnetic
Electrostatic
Nuclear
7
Q
What are the 4 ways of transferring energy from one to another?
A
Mechanically
Electrically
Heating
Radiation - light and sound waves, infrared
8
Q
What is the energy in these stores not?
A
Not fixed - can be transferred from one to another
9
Q
What is chemical energy?
A
Held in chemical bonds
10
Q
What is kinetic energy?
A
The energy that the object possesses due to its motion
11
Q
What is gravitational potential energy?
A
Position in a gravitational field
12
Q
What is elastic energy?
A
Energy stored in a stretched spring or rubber band
13
Q
What is thermal energy?
A
Heat energy
14
Q
What is magnetic energy?
A
Energy is magnets when they pull or push on things
15
Q
What is electrostatic energy?
A
Energy when things with electric charges pull or push on each other
16
Q
What is nuclear energy?
A
From breaking atoms apart
17
Q
What are the units of mass?
A
Kg
18
Q
What is a mechanical transfer?
A
When energy moves through a force making something move
19
Q
What is an electrical transfer?
A
When energy moves through electric charges
20
Q
What is heat transfer?
A
When thermal energy moves from something hot to something cooler
21
Q
What is a radiation transfer?
A
When energy is transferred through electromagnetic waves (light, sound, infrared) without needing a medium
—> can travel through space
22
Q
What is an open system?
A
A collection of matter that can gain or lose energy and matter to the ‘outside world’
23
Q
What is a closed system?
A
A collection of matter that cannot gain or lose energy and matter to the ‘outside world’
- energy can be transferred within the system
24
Q
What is the overall change of a closed system?
A
ALWAYS zero
25
What are the two types of work?
Mechanical
Electrical
26
What does mechanical work done mean?
Using a force to move an object
27
What does electrical work done mean?
When current flows
- the energy required to overcome the resistance in the wires
28
Why isn’t efficiency always transferred to the form we intend it to?
Because most devices aren’t 100% efficient
29
What is the input energy of a lamp?
Electrical energy
30
What is the output energy of a lamp?
Light and heat energy
31
What is the useful energy output from a lamp?
Light energy
32
What is the non-useful (waste) energy output from a lamp?
Heat energy
33
What is efficiency?
The proportion of the energy supplied (input energy) that’s actually transferred into the useful energy output
34
Equation for efficiency
Useful energy output
—————————— (x100 for a %)
Total energy input
35
What can the answer only be between for efficiency?
0.00 and 1.00
0% and 100%
36
Why is no device 100% efficient?
They all produce some form of waste energy
37
What is the most common form of waste energy?
Thermal energy
38
What happens when coal is burned?
The chemical energy is transferred by heating to the thermal energy store of the coal
39
How do hot coals and flames transfer energy to their surroundings?
By heating and radiation
40
What does coal have a large store of?
Chemical energy
41
What happens when a car brakes?
The brakes mechanically do work on the car to slow it down
The kinetic energy of the car decreases
The thermal energy store of the brakes increase
42
What happens when an archer fires a bow and arrow?
String of the bow is pulled back:
Chemical energy in their muscles is transferred chemically to the elastic potential of the bow
Release of the bow: the elastic potential energy of the string is transferred mechanically to the kinetic energy store of the arrow
43
What is a sankey diagram?
A visual representation of all the energy transfers taking place in a process
44
What does the thicker line or arrow in a sankey diagram mean?
The greater the amount of energy involved
45
What is each square of an arrows width equal to (sankey diagram)?
Each square = 1 joule of energy
46
What do sankey diagrams show?
The flow of energy (joules)
The power (watts) of a system
47
How is heat transferred in solids?
By conduction
48
How is heat transferred in fluids?
Via convection
49
How is heat transferred in empty space?
In the form of radiation
50
What is conduction?
Vibrating particles transfer energy to neighbouring particles
51
Why does conduction only occur in solids?
The particles are held closely together so lots of collisions occur that pass on energy
52
How does conduction work?
53
What is thermal conductivity?
How well objects transfer energy by conduction
54
Which way does heat energy flow?
From high temperature to low temperature
55
Do metals have low or high thermal conductivity?
High
- can transfer heat energy rapidly
56
Do plastics have low or high thermal conductivity?
Low
57
What do we use plastics for since they have a low thermal conductivity?
Insulators
58
Do fluids have a low or high thermal conductivity?
Low
59
What is a fluid?
A substance in which the particles are free to move around including liquids and gases
60
What does fluid in the warmer region do (convection)?
Expands as it heats up
—> becomes less dense than the cooler fluid
61
How does convection work?
62
What does convection mainly occur in?
Fluids
63
What is a convection current?
When fluids flow in a cycle due to temperature differences
64
Where do convection currents take place?
Oceans
Inside buildings - radiators warm the nearby air and set off the cycle
65
How can you reduce convection?
Stop the free flow of fluids
—> sleeping under a blanket (stopping warm air from escaping)
66
What do conduction and convection both involve?
Particles gaining kinetic energy
67
What is only transferred between the different particles in conduction?
Energy
68
What moves in convection?
The particles themselves
69
What is radiation?
Heat energy being transferred without particles (could travel through a vacuum)
70
What happens to the density of a fluid as it gets hot?
It decreases
71
What happens to the density of a fluid as it cools down?
It increases
72
What does vacuum mean?
A region of space with no particles
73
Why do birds ruffle their feathers when the weather is cold?
To trap air
74
Why do sleeping bags contain air pockets?
Air is a good insulator
75
In radiation what is energy carried by?
Infrared waves
76
What so all objects constantly do?
Absorb and emit radiation
—> do both at the same time
77
The hotter the object is the …?
More radiation it emits
78
Why does it feel hot when you put your hand over a barbecue even if you don’t touch it?
The barbecue is very hot so it is emitting a lot of infrared radiation which is absorbed by your hand
79
Which surfaces absorb and emit radiation more?
Dark, matte surfaces
80
Which surfaces absorb and emit radiation less?
Shiny, light surfaces
81
Why for dark matte surfaces absorb and emit more radiation?
They don’t reflect much light or heat so they absorb and emit more radiation
82
Why can’t shiny, light surfaces absorb and emit much radiation?
They reflect most radiation
83
What is making sure your house is sealed closed an example of?
Thermal insulation
84
Why do you want to make sure your house is sealed closed?
To stop any air from passing out of the house
—> otherwise we’d lose heat energy by convection
85
Examples of keeping your house sealed
Having foam seals around doors and windows
Houses have thick walls
Windows are double glazed
86
Why do doors and windows have foam seals around them?
To reduce heat loss by conduction
87
What are house walls made from?
Materials with a low thermal conductivity
88
What is a cavity wall?
Two layers of bricks with a small air gap/cavity between them
89
Why do houses have cavity walls?
The air gap reduces conduction (air is a poor conductor of heat)
90
Air does allow convection, so what do they fill cavity walls with?
Insulating foam
91
Insulating foam in cavity walls
Has lots of isolated air bubbles
—> gap between the wall isn’t a solid or a gas so hardly any conduction or convection occurs
92
Why are single glazed windows not great?
One layer of glass so heat is easily lost by conduction
93
Why are double glazed windows good?
Two layers of glass with tiny air gaps between them which reduces conduction as air is a bad conductor of heat
(Heat can’t be conducted from inside the house to outside the house)
94
What is friction?
The resistance that one object encounters when moving over a solid or through a liquid
95
What does friction reduce?
The efficiency of energy transfers
—> can cause the objects to heat up
96
What does friction between the cogs and chains of a bicycle do?
Makes it harder to pedal
97
What is added to the chains of a bicycle?
Oil (a lubricant) to reduce the friction which makes cycling easier
98
Why are cars and planes streamlined?
To reduce the friction from air resistance
—> allows them to use less fuel which makes the more efficient
99
What is gravity?
Forces of attraction between two objects
100
What does the size of the force of gravity depend on?
The mass of those two objects
How far apart those two objects are
101
What is the gravitational field?
Field of influence around an object
102
What is the strength of the gravitational field?
Gravitational field strength (g)
103
What is the gravitational field strength on Earth?
9.8 newtons/kg
(Usually used as 10 N/Kg)
104
What is the gravitational field strength on the moon?
1.6 newtons/kg
(Smaller than Earth)
105
When an object comes into a gravitational field what does it experience?
A force of attraction
106
What is weight?
The force acting on an object in a gravitational field
107
What is mass?
An intrinsic property of an object
- how much something weighs e.g. a human 65kg
108
Equation for weight
Mass x gravitational field strength
w = mg
109
What are the units for weight?
Newtons (N)
110
What is required to lift up an object and overcome this force of gravity?
Energy for work
111
What will energy be transferred to when lifting up an object?
To the object’s gravitation potential energy store
112
Equation for gravitational potential energy (GPE, Ep)
Mass x gravitational field strength x height
GPE = mgh
113
What are the units for GPE?
Joules (J)
114
What are the units for gravitational field strength?
N/Kg
115
What are the units for mass?
Kg
116
What are the units for height?
Metres (m)
117
What is the same everywhere in the universe?
The mass of an object
118
How much energy an object has depends on what two things?
Speed
Mass
119
The faster the speed of an object the …?
More kinetic energy it has
120
If the objects are moving at the same speed, the more mass the object has, the …?
More kinetic energy it has
121
Equation for kinetic energy
Ke = 1/2 x mass x velocity squared
Ke = 1/2mv2
122
What does Ek mean?
Energy which is kinetic
(Kinetic energy)
123
How do you covert Joules to KJ?
Divide by 1000
124
What is power?
1) the rate at which energy is transferred, P = E/t
2) the rate at which work is done, P = w/t
125
What are the units for power?
Watts (w)
126
What are the units for work done?
Joules (J)
127
Work done = …?
Energy transferred
128
What does work done mean?
The energy transfer that occurs when a force is used to move an object by a certain distance
129
Equation to use if two objects have different speeds and mass
Ek = 1/2mv2
130
Object rising (energy transfers)
Kinetic energy is transferred to the object’s GPE energy store
131
Object falling (energy transfers)
GPE is transferred to the object’s kinetic energy store
132
Kinetic energy lost = …?
GPE gained
133
Kinetic energy gained = …?
GPE lost
134
GPE gained = …?
Kinetic energy lost
135
GPE lost = …?
Kinetic energy gained
136
Equation for work done
Work done = force x distance moved
W = F x d
137
Equation for power
Power = energy transferred/time taken (P = E/t)
Power = work done/time taken (P = W/t)
