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igcse physics > energy,power,work > Flashcards

energy,power,work Flashcards

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1
Q

Energy is

If something contains a store of energy it is

If something does not store energy then it

A

the capacity of something to do work:

able to do work.

will not work.

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2
Q

The law of conservation of energy states that…

we say taht energy is

What this means is that the

A

Energy cannot be created or destroyed, it can only change from one form to another.

conserved

the total amount of energy in a closed system remains constant, although how much of each form there is may change.

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3
Q

total energy …=total energy out of

A

into system

out of system

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4
Q

the uit of all forms of energy is

A

joules

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5
Q
A
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6
Q

list all forms of energy

A

kinetic, potential, gravitational potential, nuclear , internal, chemical, elastic,

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7
Q

A falling object (in a vacuum):

describe change in energy forms

A

Gravitational potential energy → Kinetic energy

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8
Q

describe change in energy forms

A gas cooker:

A

Chemical → Internal (Heat)

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9
Q

describe change in energy forms

An LED (Light Emitting Diode):

A

Electrical → Light

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10
Q

describe change in energy forms in page 53

A
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11
Q

Conservation of Energy in Multiple Stage….

for example

A fossil fuel power station takes chemical energy (the fuel) and uses it to produce electrical energy, but the individual steps are:…

A

Many processes involve several steps before energy ends up in its final form.

Chemical → Internal (heat) → Kinetic (steam) →
Kinetic (turbine and generator) → Electrical

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12
Q

In addition to the six forms of energy mentioned above, there are four ways in which energy can be transferred from one form to another:

list them

A

forces or mechanical working

eletrical currents or electrical working

heating

waves

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13
Q

In addition to the six forms of energy mentioned above, there are four ways in which energy can be transferred from one form to another:

A
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14
Q
A
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15
Q

describe Energy Dissipation

A

When energy is transferred from one form to another, not all of the energy will end up in the desired form (or place).

This lost energy often ends up being dissipated (spreading out into the environment), usually in the form of heat, light or sound.

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16
Q

The gravitational potential energy (GPE) of an object is the…

If an object is lifted up it will…GPE.

If it falls, it will …GPE.

A

energy it has due to its height in a gravitational field:

gain

lose

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17
Q

when an object is lifted

A

the work done against gravity is transformed into gravitational potential energy

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18
Q

gravitational potential energy is abbrevieted in

A

g.p.e.

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19
Q

the change in g.p.e. can be expreesed in the formula

A
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20
Q

The gravitational field strength (g) on the Earth is approximately

A

10 N/kg.

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21
Q

The kinetic energy (k.e) of an object is the

A

energy it has as a result of its speed.

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22
Q

when speed and velocity increase ….

A

k.e. increases

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23
Q

kinetic energy is related to the mass (m) and speed (v) of the object by the equation:

A
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24
Q
A
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25
Q

do problem page 56

A
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26
Q

calculate speed using k.e. formula

A

root 2k.e./m

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27
Q

the size of the velocity is equal to the …of the object

A

speed

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28
Q

when a car travels at constant speed, its kinetic energy is …as its …

the car still needs fuel(…)

to keep moving at a constant speed because it is doing

A

constant

speed not changing

chemical energy

work against frictional forces

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29
Q

do problem page 55

A
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30
Q

Energy resources are

A

large banks of energy that can be transferred into a form that can be used by society,

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31
Q

list the main energy resources and their energy form

A
32
Q

describe the main energy resources and their energy form

A
33
Q
A
34
Q
A
35
Q

A renewable energy resource is one that

A

is replenished at a faster rate than the rate at which it is being used.

36
Q

A reliable energy resource is one that can

A

roduce energy at any time.
Non-reliable resources can only produce energy some of the time (e.g. when it’s windy).

37
Q
A
38
Q

Most of our energy resources on the Earth come from the

A

Sun

39
Q
A
40
Q

Most of our energy resources on the Earth come from the Sun:

A

The Sun heats up the atmosphere, creating wind and producing waves.

Water evaporated by the Sun falls as rain, filling up reservoirs.

Plants grown using sunlight form the basis for fuels – both biofuels and fossil fuels.

41
Q

The Sun’s energy is produced by through the process of

A

The Sun’s energy is produced by through the process of nuclear fusion in its core.

42
Q

Nuclear fusion involves

A

the collision (and bonding) of hydrogen nuclei to form helium nuclei, releasing nuclear energy in the process.

43
Q

Some forms of energy, however, do not come from the Sun.
These include:

A

Geothermal – this comes from heat produced in the Earth’s core.

Nuclear – this comes from elements which make up a small proportion of the Earth’s crust.

Tidal – this comes (mainly) from the gravitational attraction of the moon.

44
Q
A
45
Q

Whenever energy is transferred from one form to another, some of that energy is

A

usually wasted and is transferred away from the system usually in the form of heat or waves (light and sound).

46
Q

An efficient system is one where

A

most of the energy going into that system ends up in the form that is wanted.

47
Q

An inefficient system is one where

A

most of the energy ends up in forms that weren’t wanted.

E.g. An old incandescent light bulb is inefficient because only a small amount of the electrical energy (5%) ends up as light.

48
Q
A
49
Q

The efficiency of a system is

A

the percentage of energy transferred from the original store that ends up in the intended form.

50
Q
A
51
Q

Efficiency can be calculated using the following equation:

A
52
Q

Efficiency can also be written in terms of power (the energy per second):

A
53
Q

Work is done whenever

The greater the force, the… the work

The larger the distance moved, the…. the work.

A

a force acts on an object that moves (or is moving) in the direction of the force.

greater

larger

54
Q

Whenever any work is done,

The amount of energy transferred (in joules)

A

Whenever any work is done, energy

is equal to the work done (also in joules).

energy transferred (J) = work done (J)

55
Q
A
56
Q
A
57
Q

Usually, if a force acts in the direction that an object is moving then the object will

A

gain energy.

58
Q

If the force acts in the opposite direction to the movement then the object

A

lose energy.

59
Q
A
60
Q

The amount of work that is done if related to the size of the force, and the distance moved by the object, in the direction of the force:

A
61
Q

The units of work are … but can also be given as

A

joules (J)

(Nm).

62
Q

The power of a machine is

A

the rate at which the machine transfers energy.

63
Q

The greater the rate at which energy is transferred,the ….

A

greater the power.

64
Q

power is equal to …

because

A

equal to the rate at which work is done.

Because work done is equal to energy transferred,

65
Q
A
66
Q

Power is the

A

amount of energy transferred (or work done) every second.

67
Q

Power, work and time are related by the following equation:

A
68
Q

The unit of power is the..

which is the same as

A

watt (W

a joule per second (J/s).

69
Q

Think of power as

A

“energy per second”.

Thinking of it this way will help you to remember the relationship between power and energy.

And to help you remember the unit of power: “Watt is the unit of power?”

70
Q

describe solar energy

A

it makes use of energy from the sun

solar cells, wnown as photovoltaic cells convert light energy into electricity

71
Q

wind energy

A

uses wind to turn turbines

wind energy turns the turbine blades in a wind turbine

the kinetic energy of the wind is conveted into electrical energy by the generator

72
Q

wave energy

A

makes use of ocean waves to turn turbines

generatior are driven by the trasverse motion of waves.

the kinetic energy of the wave motion causes water to rise and fall in the air chamber

the air above the water causes the turbine to turn and electricity is produced by the generator

73
Q

tidal energy

A

makes use of incoming and outgoing tides

tidal energy causes the water to move

it turns the turbine and electricity is generated

g.p.e. and k.e. convert into elecrical energy

74
Q

geothermal energy

A

uses heat from the earth’score

water is fed down through pipes several kilometres

underground, passing through hot rocks

these rocks heat the water until it turns into very hot steam.

the steam is fed back up to the ground level and is used to turn turbines and generate electricity

75
Q

hydroelectric energy

A

uses a dam to trap water

a dam is built to trap water, sometimes in a valley where there is an existing lake. Water is allowed to flow through tunnels in the dam, to turn turbines and thus drive the generators that produce electricity

igcse physics (10 decks)

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