Energy Flashcards
1
Q
What are the units of energy?
A
Joules (J)
2
Q
What are the units of 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 are the 8 energy stores?
A
Chemical
Kinetic
Gravitational potential
Elastic
Thermal
Magnetic
Electrostatic
Nuclear
6
Q
What are the 4 ways of transferring energy from one to another?
A
Mechanically
Electrically
Heating
Radiation
7
Q
What is chemical energy?
A
Held in chemical bonds
8
Q
What is kinetic energy?
A
Energy that the object possesses, due to its motion
9
Q
What is gravitational potential energy?
A
Position in a gravitational field
10
Q
What is elastic energy?
A
Energy stored in a stretched spring or rubber band
11
Q
What is thermal energy?
A
Heat energy
12
Q
What is magnetic energy?
A
Energy in magnets when they pull or push on things
13
Q
What is electrostatic energy?
A
Energy when things with electric charges pull or push on each other
E.g. an electric shock from a light switch
14
Q
What is nuclear energy?
A
From breaking atoms apart
—> stored in the nucleus of an atom
15
Q
Equation for density
A
Density = mass/volume
16
Q
What are the units of volume?
A
m3
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
Example of a mechanical transfer
A
Stretching a rubber band
20
Q
What is an electrical transfer?
A
When energy moves through electric charges
21
Q
Example of electrical transfer
A
Plugging something into a socket
22
Q
What is heat transfer?
A
When thermal energy moves from something hot to something cooler
23
Q
Example of heat transfer
A
A pan on a stove
24
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
25
Example of radiation sound
Opera singer singing
26
Example of radiation light
Light bulb is illuminated
27
Example of infrared radiation
Feeling the heat from a campfire
28
Is metal a conductor or an insulator?
Conductor
29
Is air a conductor or insulator?
Insulator
30
What is a collection of matter (group of objects) called?
System
31
What happens when a system changes?
Energy is transferred either between objects or between different forms
32
Why isn’t efficiency always transferred to the form we intend it to?
Because most devices aren’t 100% efficient
33
What is the input energy of a lamp?
Electrical energy
34
What is the output energy of a lamp?
Light and heat energy
35
What is the useful energy output from a lamp?
Light energy
36
What is the non-useful (waste) energy output from a lamp?
Heat energy
37
What is efficiency?
The proportion of the energy supplied (input energy) that’s actually transferred into the useful energy output
38
Equation for efficiency
Useful energy output
—————————— (x100 for a %)
Total energy input
39
What can the answer only be between for efficiency?
0.00 and 1.00
0% and 100%
40
What is the most common form of waste energy?
Thermal energy
41
What happens when coal is burned?
The chemical energy is transferred by heating to the thermal energy store of the coal
42
How do hot coals and flames transfer energy to their surroundings?
By heating and radiation
43
What does coal has a large store of?
Chemical energy
44
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
45
What happens when an archer fires a bow and arrow?
String or 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 stored of the arrow
46
What is a sankey diagram?
A visual representation of all the energy transfers taking place in a process
47
What does the thicker the line or arrow in a sankey diagram mean?
The greater the amount of energy involved
48
What is each square of an arrows width equal to? (Sankey diagram)
Equal to 1 joule of energy
49
What do sankey diagrams show?
The flow of energy (joules)
The power (watts) of a system
50
How is heat transferred in solids?
By conduction
51
How is heat transferred in fluids?
Via convection
52
How is heat transferred in empty space?
In the form of radiation
53
What is conduction?
Vibrating particles transfer energy to neighbouring particles
54
Why does conduction only occur in solids?
The particles are closely held together
—> lots of collisions that pass on energy
55
How does conduction work?
The heat warms up the particles giving them kinetic energy
They vibrate and when they collide with neighbouring particles they transfer kinetic energy
The neighbours will also vibrate faster and collide more with their neighbours
—> process repeats until the heat is spread out evenly
56
What is thermal conductivity?
How well objects transfer energy by conduction
57
Which way does heat energy flow?
From high temperature to low temperature
58
Metals (conduction)
Metals have high thermal conductivity
—> transfer heat energy rapidly
59
Plastics (conduction)
Plastics have low thermal conductivity
60
What do we use plastics for, since they have a low thermal conductivity?
Insulators
61
Fluids (conduction)
Low thermal conductivity
62
What is a fluid?
Liquid
Gas
—> as they can flow
63
What does fluid in the warmer region do? (Convection)
Expands as it heats up
—> becomes less dense than the cooler fluid
64
How does convection work?
1) particles near the heat source gain kinetic energy and spread out becoming less dense
2) since their less dense they rise above the colder particles
3) at the same time the cooler particles sink down and heat up, gaining kinetic energy
4) whilst happening the hot particles lose their energy and cool down and sink to the bottom
—> cycle keeps repeating for as long as the fluid was being heated
65
What is it called when fluids flow in a cycle due to temperature differences?
Convection current
66
Where do convection currents take place?
Oceans
Inside buildings - radiators warm the nearby air and set off the cycle
67
How can you reduce convection?
Stop the free flow of fluids
—> sleeping under a blanket (stopping warm air from escaping)
68
What do conduction and convection both involve?
Particles gaining kinetic energy
69
What is only transferred between the different particles in conduction?
Energy
70
What moves in convection?
The particles themselves
71
What is radiation?
Heat energy being transferred without particles (could travel through a vacuum)
72
What happens to the density of a fluid as it gets hot?
It decreases
73
What happens to the density of a fluid as it cools down?
It increases
74
What is a convection current?
When a fluid flows in a cycle due to temperature differences
75
What does vacuum mean?
A region of space with no particles
76
Why do birds ruffle their feathers when the weather is cold?
To trap air
77
Why do sleeping bags contain air pockets?
Air is a good insulator
78
In radiation what is energy carried by?
Infrared waves
79
What do all objects constantly do?
Absorb and emit radiation
—> do both at the same time
80
The hotter the object is …
The more radiation it emits
81
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 it is emitting a lot of infrared radiation which is absorbed by your hand
82
Which surfaces absorb and emit radiation more than shiny, light surfaces?
Dark, matte surfaces
83
Why do dark, matte surfaces absorb more radiation than light, shiny surfaces?
They don’t reflect much light or heat so they absorb more radiation instead of bouncing it away
84
Why do dark, matte surfaces emit more radiation than shiny, light surfaces?
Because they absorb more radiation
Shiny, light surfaces don’t absorb much radiation so can’t emit much radiation and they tend to reflect radiation back in
85
What is making sure your house is sealed closed an example of?
Thermal insulation
86
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
87
What are examples of keeping your house seal closed?
Have foam seals around doors and windows
Houses have thick walls
Windows are double glazed
88
Why do doors and windows have foam seals around them?
To reduce heat loss by conduction
89
What are house walls made from?
Materials with a low thermal conductivity
90
What is a cavity wall?
Two layers of bricks with a small air gap/cavity between them
91
Why do houses have cavity walls?
The air gap reduces conduction (air is a poor conductor of heat)
92
Air does allow convection, so what do they fill cavity walls with?
Insulating foam
93
Insulating foam in cavity walls
Has lots of isolated air bubbles
—> gas between the wall isn’t a solid or a gas so hardly any conduction or convection occurs
94
Why are single glazed windows not great?
One layer of glass
—> heat is easily lost by conduction
95
Why are double glazed windows good?
Two layers of glass with a tiny air gap between them
—> reduces conduction as heat can’t be conducted across the air gap
(Heat can’t be conducted from inside the house to outside the house)
96
What is friction?
The resistance that one object encounters when moving over a solid or through a liquid
97
What does friction reduce?
The efficiency of energy transfers
—> can cause the objects to heat up
98
What does friction between the cogs and chains of a bicycle do?
Makes it harder to pedal
99
What is added to the chains of a bicycle?
Oil (a lubricant) to reduce the friction
—> makes the cycling easier
100
Why are cars and planes streamlined?
To reduce the friction from air resistance
—> allows them to use less fuel - makes them more efficient
101
What is gravity?
Forces of attraction between two objects
102
What does the size of the force of gravity depend on?
The mass of those two objects
How far apart those two objects are
103
What is the gravitational field?
Field of influence around an object
104
What is the strength of the gravitational field called?
Gravitational field strength (g)
105
What is the gravitational field strength on Earth?
9.8 newtons/kg
106
What is the gravitational field strength on the moon?
1.6 newtons/kg (smaller than Earth)
107
When an object comes into a gravitation field what does it experience?
A force of attraction
108
What is the force of attraction referred to as?
An object’s weight
109
Equation for weight
Mass x gravitational field strength
110
What is weight measured in?
Newtons (N)
111
What is weight?
The force acting on an object due to gravity
112
What is mass?
How much something weighs
E.g. a human = 65kg
113
What is required to lift up an object and overcome this force of gravity?
Energy or work
114
What will energy be transferred to when lifting up an object?
To the object’s gravitational potential energy store
115
Equation for gravitational potential energy (GPE, Ep)
Mass x gravitational field strength x height
mgh
116
What is GPE measured in?
Joules (J)
117
What is mass measured in?
Kg
118
What is the gravitational field strength measured in?
N/kg
119
What is height measured in?
Metres (m)
120
What is the same anywhere in the universe?
The mass of an object
121
How much energy an object has depends on what two things?
Speed
Mass
122
The faster the speed of an object the more …
Kinetic energy it has
123
If the objects are moving at the same speed, the more mass the object has the more …
Kinetic energy it has
124
Equation for kinetic energy
1/2 x mass x velocity squared
1/2mv2
125
Ek means?
(Kinetic) energy
126
Joules —> kJ
Divide by 1000
