State the 8 different stores of energy
Magnetic potential energy
Gravitational potential energy
Chemical potential 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.
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)
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
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
Not useful energy transfers
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.
What are the energy transfers of a kettle
electrical potential energy --> thermal energy, sound energy and kinetic energy
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
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 this formula
Power = current x potential difference
P = IV
Current is measured in Amps (A)
Potential difference is measured in Volts (V)
Explain how you calculate the useful power output 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
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
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.