Energy up to level 6 Flashcards
State the 10 different stores of energy
Magnetic potential energy
Kinetic energy
Thermal energy
Light energy
Gravitational potential energy
Chemical potential energy
Sound energy
Elastic potential energy
Electric potential energy
Nuclear potential energy
What are the energy transfers for a torch
Chemical potential energy –> Electric potential energy –> Light energy
What are the energy transfers for a falling ball?
Gravitational potential energy –> Kinetic energy –> Sound and thermal energy
What is the law of conservation of energy?
Energy cannot be created or destroyed, it can only be transferred from one store to another
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.
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
How do you calculate the energy transferred by a force?
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’
Explain how energy is transferred when you apply the breaks on a car
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)
What does the term ‘energy dissipation’ mean?
How does it happen?
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.
What are the energy transfers in a bungee cord?
Gravitational potential energy –> kinetic energy –> elastic potential energy –> kinetic energy –> Gravitational potential energy
Why is it possible that humans might ‘run out’ of energy even though it cannot be created or destroyed
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.
What is the unit of energy?
The Joule (J)
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?
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
State the equation to calculate gravitational potential energy.
What are the units that each part of the equation is measured in?
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)
Explain why lifting an object up 10m on Jupiter stores more gravitational potential energy than lifting the same object up 10m on Earth
this is becuase Jupiter has a stronger gravitational field strenght than Earth. This means it has a stronger acceleration due to gravity (g).
As gravitational potential energy = m x g x h. If g is larger then gravitational potential energy is also larger.
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.
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
How do you calculate the energy in the elastic potential energy store of a spring?
Example: What is the elastic potential energy stored in a spring with a spring constant of 4 N/m which is extended by 2m?
The elastic potential energy of a spring can be found by
elastic potential energy = 1/2 x spring constant x extension squared
EPE = 1/2 x k x e2
Elastic potential energy is measured in joules (J)
Spring constant is measured in Newtons per meter (N/m)
Extension is measured in meters (m)
Example: elastic potential energy = 1/2 x 4 x 22
8 J
Describe the energy changes of a catapault
elastic potential energy –> kinetic energy
What are the useful and not useful energy stores that a car transfers energy into
Useful energy transfers
Kinetic energy
Light energy
Not useful energy transfers
Sound energy
Thermal energy
What factors affect the size of the friction force acting between an object and the floor it is sliding over
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
What are the two formula for calculating the eficiency of an energy transfer?
Efficiency = useful energy output/total energy input x 100%
Efficiency = useful power output/total energy input x 100%
Why do we try to make the energy transfers of machines as efficient as possible?
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.
Explain why the efficiency of an energy transfer can never be more than 100%.
The law of conservation of energy states that energy cannot be created or destroyed. If an energy transfer was more than 100% then the energy output would be greater than the energy input. This means that energy would have to be created, which would break the law of conservation of energy.
What are the energy transfers of a kettle
electrical potential energy –> thermal energy, sound energy and kinetic energy
What are the energy transfers of a filament light bulb
Which of these transfers are useful and which ones are not useful?
The energy transfers of a filament light bulb are:
Electrical potential energy –> light energy and thermal energy
electrical potential energy to light energy is useful
electrical potential energy to thermal energy is not useful
What are the main differences between the operation of a mains power device and a battery powered device.
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)
Define the term power
What is the equation for power?
What are the units of the terms in the equation?
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)
How do you calculate the power of an electrical device?
The power of an electrical device can be found from these to formula
Power = current x potential difference
P = IV
and
Power = current squared x resistance
P = I2R
Power is measured in watts (W)
Current is measured in Amps (A)
Potential difference is measured in Volts (V)
Resistance is measured in Ohms
Explain how you calculate the wasted power of a light bulb that has a power input of 200W and an efficiency of 5%
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
The energy disspated as heat = total input - useful output
= 200 - 10
= 190 W
What do the terms thermal conductor and thermal insulator mean?
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
How does cavity wall insulation help to reduce heat loss from your house?
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
Why are frying pans made of metal, but have plastic handles?
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
What is the effect of the colour of a surface on heating and cooling?
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.
How does heat transfer by radiation?
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
What happens to the movement of the particles in solids, liquids and gasses when they are heated up.
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
Describe 5 ways that you can reduce heat loss through your house
- Cavity wall insulation can reduce the heat lost through your walls
- Loft insulation can reduce heat loss through the roof
- Placing reflective foil behind radiators can reduce heat loss through walls
- Double glazing your windows can stop heat being lost through the windows
- Draft excluders can stop the warm air from escaping and being replaced by cold air (convection)
What is the relationship between the rate of infrared radiation emission and the rate of cooling?
The faster an object emits infra-red radiation, the faster it cools.
What is the link between the rate of infra-red radiaiton absobtion and the rate of heating
The faster an object absorbs infra-red radiaiotn
Sketch a graph of how the temperature of an object changes with time as it cools and explain its shape
When an object cools, it starts off cooling very fast and the rate of cooling gets slower over time.
This is becuase how fast something cools depends on the size of the temperature difference between the object and the environment. The larger the temperature difference the faster something will cool
What is infra-red radiation?
Infra red radiaiton is an electromagnetic wave with a wavelength that is longer than red light
What is global warming?
Global warming is the gradual warming of the earth becuase heat is trapped in the atmosphere by greenhouse gasses (carbon dioxide and methane)
Explain how the greenhouse effect causes global warming
The greenhouse effect occurs because energy from the sun travels to the earth as visible light. This can pass through the greenhouse gasses in the atmosphere and is absorbed by the earth.
When the energy is emitted back away from the earth, it is emitted as infra-red radiation. This radiation cannot pass through the greenhouse gasses so it gets trapped in the atomsphere of the earth.
As the energy does not leave the earth it causes the earth to warm up. This is global warming
What is specific heat capacity?
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
What factors affect how much energy it takes to heat something up?
- The temperature change (how much you heat it up by)
- The material (specific heat capacity - how hard it is to heat up)
- The mass (Things with more mass are harder to heat up)
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
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
What is payback time?
How do you calculate the payback time of a home improvement?
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
How does cavity wall and loft insulation work?
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.
Give some examples of renewable and non-renewable energy generation
Non-renewable
Fossil fuels (coal, crude oil and natural gas)
Nuclear
Renewable
Wind
Solar
Geothermal
Biomass
Tidal
Wave
Hydroelectric
Explain why biofuels are carbon neutral but fossil fuels are not
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.
In general, what are the advantages and disadvantages of renewable energy generation?
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
What is the difference between a solar cell and a solar heating system?
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
Explain how geothermal energy is generated
When radioactive rocks underneath the earths surface decay, they release radiaiton that warms up the surrounding rocks.
By pumpuing water down to these hot rocks and back up again we can heat up the water. This can be used for heating, or turned into steam to spin a generator which generates electricity.
Explain the environmental problems caused by burning fossil fuels
- Global warming - burning fossil fuels releases carbon dioxide, which is a greenhouse gas. This traps heat around the earth, causing global warming
- 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.
What are the problems caused by nuclear waste from nuclear power stations?
- The waste is radioactive and people need to be protected from the radiation
- 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
What is the start up time of a power station?
This is the time it takes for the power station to turn on and start generating electricity
Rank the start up times of these power stations from shortest to longest:
coal
oil
Natural gas
Nuclear
Shortest: Natural gass
oil
coal
Longest: Nuclear
What are the problems caused by global warming?
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)
What are the problems caused by acid rain?
Damage to buildings and statues
Lakes become acidic, killing fish
Soil becomes acidic, killing plants
What is carbon capture and storage?
This is when carbon dioxide that is released from fossil fuel power stations is captured intead of being released into the envronment. We can then put it back into the ground so it does not contribute to global warming.
