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GCSE physics foundation > Energy > Flashcards

Energy Flashcards

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1
Q

State the 8 different stores of energy

A

Magnetic potential energy

Kinetic energy

Thermal energy

Gravitational potential energy

Chemical potential energy

Elastic potential energy

Electric potential energy

Nuclear potential energy

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2
Q

What are the energy transfers for a torch

A

Chemical potential energy –> Electric potential energy –> Light energy

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3
Q

What are the energy transfers for a falling ball?

A

Gravitational potential energy –> Kinetic energy –> Sound and thermal energy

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4
Q

What is the law of conservation of energy?

A

Energy cannot be created or destroyed, it can only be transferred from one store to another

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5
Q

A car with an energy input of 500,000J from chemical potential energy transfers 350,000J into kinetic energy and 25,000J into light energy. Explain how you would calculate the energy it transfers into the thermal energy store.

A

The law of conservation of energy states that the total energy at the start and end of the process is the same.

This means that the total energy output must be 500,000J, becuase the total energy input is 500,000J. This means thermal energy is 500,000 - 350,000 - 25,000 = 125,000J

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6
Q

How do you calculate the energy transferred by a force?

A

Force transfer energy when they act over a distance. The formula relating force and distance is:

Work done (J) = Force (N) x distance (m)

‘Work done’ is the scientic way of saying ‘energy transferred’

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7
Q

Explain how energy is transferred when you apply the breaks on a car

A

When you apply the breaks on a car a force acts over a distance. This means that energy is transferred.

The transfers of energy are from the kinetic energy store (the car slows down) into the thermal energy store (the breaks get hotter)

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8
Q

What does the term ‘energy dissipation’ mean?

How does it happen?

A

Energy dissipation means that energy is transferred into stores where humans cannot make use of it.

The most common form of energy dissipation is when the energy is transferred into thermal energy in the environment. When this occurs the energy becomes ‘spread out’ and we are unable to access it.

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9
Q

Why is it possible that humans might ‘run out’ of energy even though it cannot be created or destroyed

A

When we transfer energy, some of it is dissipated into thermal energy in the environment, where we cannot access it. The energy is still present but we are unable to make use of it, so we could run out of the energy that we are able to use.

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10
Q

What is the unit of energy?

A

The Joule (J)

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11
Q

How would you calculate the distance that you would have to push an object with a force of 15N to transfer a force of 90N?

A

The equation for work done can be placed in an equation triangle to help rearrange it.

Coving up distance gives work ÷ force = 90 ÷ 15 = 6m

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12
Q

State the equation to calculate gravitational potential energy.

What are the units that each part of the equation is measured in?

A

Gravitational potential energy = mass x acceleration due to gravity x height

GPE = m x g x h

Gravitaitonal potential energy is measured in Joules (J)

Mass is measured in kilograms (kg)

Acceleration due to gravity is measured in meters per second squared (m/s2)

Height is measured in meters(m)

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13
Q

How do you calculate the amount of energy stored in the kinetic energy store of an object.

Example calculation: what is the kinetic energy store of an object that is moving at 5 m/s and has a mass of 10kg.

A

The kinetic energy store of an object can be calculated from this equation

Kinetic energy= 1/2 x mass x velocity squared

KE = 1/2 x m x v2

Mass is measured in kilograms (kg)

velocity is measured in meters per second (m/s)

Kinetice energy is measured in joules (J)

Example = 1/2 x 10 x 52

= 125J

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14
Q

Describe the energy changes of a catapault

A

elastic potential energy –> kinetic energy

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15
Q

What are the useful and not useful energy stores that a car transfers energy into

A

Useful energy transfers

Kinetic energy

Light energy

Not useful energy transfers

Sound energy

Thermal energy

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16
Q

What factors affect the size of the friction force acting between an object and the floor it is sliding over

A

The friction force increases if the object has a higher mass and if the surface of the object or the floor is rougher.

Lubricants, such as oil, wil reduce the size of the friction force by reducing the roughness of the surface

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17
Q

What are the two formula for calculating the eficiency of an energy transfer?

A

Efficiency = useful energy output/total energy input x 100%

Efficiency = useful power output/total energy input x 100%

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18
Q

Why do we try to make the energy transfers of machines as efficient as possible?

A

When a process is more efficient there is less energy dissipated as thermal energy and transferred into other not useful forms. This means that you do not have to put as much extra energy into the energy transfer to get the energy output that you want.

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19
Q

What are the energy transfers of a kettle

A

electrical potential energy –> thermal energy, sound energy and kinetic energy

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20
Q

What are the main differences between the operation of a mains power device and a battery powered device.

A

A mains power device has a much higher potential difference, which means that it has a much higher power. They therfore can peform larger tasks, but also makes it more dangerous if there is a short circuit or a problem with the device

Mains power devices work on alternating current (the electric current moves backwards and forwards) while battery powered devices work on direct current (the current only goes one way)

21
Q

Define the term power

What is the equation for power?

What are the units of the terms in the equation?

A

Power is the rate of transfer of energy (how fast energy is transferred)

Power = energy/time

P=E/t

Power is measured in Watts (W)

Energy is measured in Joules (J)

time is measured in seconds (s)

22
Q

How do you calculate the power of an electrical device?

A

The power of an electrical device can be found from this formula

Power = current x potential difference

P = IV

Current is measured in Amps (A)

Potential difference is measured in Volts (V)

23
Q

Explain how you calculate the useful power output of a light bulb that has a power input of 200W and an efficiency of 5%

A

First you find the power that is transferred usefully using the efficiency equation

efficiency = useful power output/total power input x 100

therefore useful power output = efficiency x total power input/100

= 10W

24
Q

What do the terms thermal conductor and thermal insulator mean?

A

A thermal conductor is a matrial that allows heat to transfer through it easily

A thermal insulator does not allow heat to transfer through it easily

25
Q

How does cavity wall insulation help to reduce heat loss from your house?

A

Cavity wall insulation is a better insulator than the brick and the air cavity. This means that it does not let heat pass through it as quickly, reducing the heat loss from your house

26
Q

Why are frying pans made of metal, but have plastic handles?

A

Frying pans are made of metal becuase metal is a good thermal conductor, it allows heat to pass from the hob to the food.

The handles are made of plastic because plastic is a good thermal insulator. It means the heat does not conduct down the handle, so you do not burn yourself when you pick the pan up

27
Q

What is the effect of the colour of a surface on heating and cooling?

A

Dark coloured surfaces absorb heat quickly and emit heat quickly

Light coloured surfaces reflect more of the heat that hits it through radiation. This means that they absorb and emit heat much more slowly.

28
Q

How does heat transfer by radiation?

A

One way that heat can be transfered is through infra-red radiation, which is a type of light wave that we cannot see.

When an object absorbs infra-red radiaiton it heats up. When it emits infra-red radiation it cools down

29
Q

What happens to the movement of the particles in solids, liquids and gasses when they are heated up.

A

In all states of matter, the particles will move more when a substance is heated up.

In solids this means that the particles vibrate backwards and forwards faster

In liquids and gasses it means that the particles move about more quickly

30
Q

What is the relationship between the rate of infrared radiation emission and the rate of cooling?

A

The faster an object emits infra-red radiation, the faster it cools.

31
Q

What is the link between the rate of infra-red radiaiton absobtion and the rate of heating

A

The faster an object absorbs infra-red radiaiotn

32
Q

What is specific heat capacity?

A

Specific heat capacity measures how much energy it takes to heat something up.

If something has a high specific heat capacity it takes a lot of energy to heat it up, this means it is hard to make it heat up or cool down.

Something with a low specific heat capacity is easy to heat up or cool down becuase it does not take a lot of energy to change its temperature

33
Q

What factors affect how much energy it takes to heat something up?

A
  1. The temperature change (how much you heat it up by)
  2. The material (specific heat capacity - how hard it is to heat up)
  3. The mass (Things with more mass are harder to heat up)
34
Q

How to you calculate the amount of energy needed to heat something up?

What are the units for the equation?

Example: how much energy does it take to heat up a 3kg platinum block by 10 degrees. The specific heat capacity of platinum is 126 J/kg

A

The amount of energy needed to heat something up can be found from the specific heat capacity equation

Energy = mass x specific heat capapcity x change of temperature

E = m x c x T

Energy is measured in Joules (J)

mass is measured in kilograms (kg)

temperature is measured in degrees celcius (oC)

specific heat capacity is measured in joules per kilogram per degree celcius (J/kgoC)

Example: 3 x 126 x 10 = 3780J

35
Q

What is payback time?

How do you calculate the payback time of a home improvement?

A

Payback time is the time it takes for a money saving device to save back the cost of having it installed

To calculate the payback time you use the equation:

Payback time (years) = cost of installation ÷ the money saved per year

36
Q

How does cavity wall and loft insulation work?

A

The insulating material traps pockets of air. Air is a good insulator as long as it is not allowed to move. The pockets of air do not let the thermal energy pass through it very easily, so the energy does not leave your house.

37
Q

Give some examples of renewable and non-renewable energy generation

A

Non-renewable

Fossil fuels (coal, crude oil and natural gas)

Nuclear

Renewable

Wind

Solar

Geothermal

Biomass

Tidal

Wave

Hydroelectric

38
Q

Explain why biofuels are carbon neutral but fossil fuels are not

A

Fossil fuels contain the carbon from plants that died millions of years ago. By burning them carbon dioxide is released into the atomsphere, which causes a rise in carbon dioxide levels in the short term

Biofuels are fuels that are made by bacteria. The bacteria remove carbon dioxide from the air via photosynthesis to make the fuel. When the fuel is burnt it only releases carbon into the air which has recently been removed from it. This makes them carbon neutral.

39
Q

In general, what are the advantages and disadvantages of renewable energy generation?

A

Advantages

They are renewable so they will not run out

They do not contribute to global warming through the emission of greenhouse gasses

Disadvantages

They are unreliable - most of them only work in certain weather conditions

They rely on the environment so can only be built in certain areas

They are much more expensive to build than fossil fuel power stations

40
Q

What is the difference between a solar cell and a solar heating system?

A

A solar cell transfers light energy into electrical potential energy which can be used to power electrical equipment

A solar heating system absobs energy from the sun to heat water, which can be used to heat are homes and provide hot tap water

41
Q

Explain the environmental problems caused by burning fossil fuels

A
  1. Global warming - burning fossil fuels releases carbon dioxide, which is a greenhouse gas. This traps heat around the earth, causing global warming
  2. Acid rain - Burning fossil fuels produces sulphur dioxide. This mixes with the water in clouds to form sulphuric acid, which then falls as acid rain.

When car engines get hot they react the nitrogen in the air with oxygen to form nitrogen oxide, this forms nitric acid in the air, contributing to acid rain.

42
Q

What are the problems caused by nuclear waste from nuclear power stations?

A
  1. The waste is radioactive and people need to be protected from the radiation
  2. The waste can be turned into nuclear bombs so needs to be guarded

It costs a lot of money to protect people from these two problems in the long term

43
Q

What is the start up time of a power station?

A

This is the time it takes for the power station to turn on and start generating electricity

44
Q

Rank the start up times of these power stations from shortest to longest:

coal

oil

Natural gas

Nuclear

A

Shortest: Natural gass

oil

coal

Longest: Nuclear

45
Q

What are the problems caused by global warming?

A

Ice caps melt causing sea levels to rise

Hotter weather means disease carrying (malaria) mosquitos move north towards the UK

Worse weather (e.g. storms)

46
Q

What are the problems caused by acid rain?

A

Damage to buildings and statues

Lakes become acidic, killing fish

Soil becomes acidic, killing plants

47
Q

State the 5 transfers of energy

A

Heat

Sound

Light

Force

Electric current

48
Q

What is the main problem caused by fossil fuels?

A

global warming

49
Q

State 5 ways that you can reduce heat loss from a house

A
  1. Cavity wall insulation can reduce the heat lost through your walls
  2. Loft insulation can reduce heat loss through the roof
  3. Placing reflective foil behind radiators can reduce heat loss through walls
  4. Double glazing your windows can stop heat being lost through the windows
  5. Draft excluders can stop the warm air from escaping and being replaced by cold air (convection)

GCSE physics foundation (7 decks)

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