# Physics core and adtitional (P1,P2)

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Physics Unit 1 Revision
Energy
There are 9 different forms of energy:
Light Heat Chemical Kinetic (movement) Electrical
Elastic (Gravitational) potential Nuclear Sound
Energy is never created or destroyed! Energy is transferred from one form to
another form. Not all of the energy transferred by a device is useful energy.
Potential energy is stored energy. All energy will eventually spread out to the
surroundings as heat.
Sankey diagrams and efficiency
Sankey diagrams are ways of representing the different energy transformations
that take place in different electrical
devices. The start of the sankey
diagram shows the total energy going
into the device. The diagram then
splits off into different sized arrows to
represent the other energy transfers
that take place, the bigger the arrow
the larger the energy. The energy
entering the device must equal the
energy leaving the device.
To know how good a device is at transferring energy you need to be able to
calculate the efficiency. To do that you need to use the following equation (which
will be given in the exam)
OR
So for the above example the answer would be

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The closer the efficiency is to 1 the more useful energy the device is transferring.
So for the light bulb example we got an efficiency of 0.1, so the light bulb isn't
very good and transferring useful energy.…read more

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Kinetic theory
Most matter or substances can be classed as being solids, liquids or gases.
Solids: They have the least amount of energy are
arranged in a pattern. They vibrate around fixed
positions
Liquids: The particles are closely packed together but
can move about freely over one another.
Gases: They have the most amount of energy and move
around at high speeds and can collide with one another.
Matter can also change from one state to
another e.g. ice to water to water vapour.…read more

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This makes the average
kinetic energy of the remaining particles less and the temperature goes down.
Condensation is when a liquid turns to a gas, like water forming on a cold window.
The rate of condensation can be increased by 2 things
Bigger surface area
Reducing the surface temperature
Heat transfer
Heat can be transferred quicker if the temperature difference between the
substance and surroundings is greater.
Heat can be transfer by 3 methods
Conduction: Occurs in solids and felt by direct physical contact.…read more

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You can prevent heat loss from objects by using insulation. Air and other gases
are bad conductors of heat but make good insulators. For convection you must
stop the heat from rising e.g. using a lid.
Trapped air helps to prevent heat loss by conduction and convection. A vacuum
(empty space with no particles) also stops conduction and convection as those
methods need particles to transfer heat
Radiation can be reduced by using light reflective surfaces.…read more

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Specific heat capacity
Specific heat capacity is the amount of energy needed to raise the temperature
of a 1 kilogram substance by 1°C. If an object has a low specific heat capacity
then it is quick to heat up, if it has a large specific heat capacity then it will take
longer to heat up as it needed more energy.…read more

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Which coloured surface heated up quicker and explain your answer?
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(b) The water in the can with the dull black surface began at 20°C and rose to 80°C. The mass of water
in the can is 100g. Calculate the energy gained by the water.
Specific heat capacity of water is 4200 J/kg °C
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......(4)(Total 6 marks)
Sample Question 11
The picture shows one type of solar water heater.…read more

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Explain why the copper pipes inside the solar panel are painted black.
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(2)
(b) Each day the average European family uses 100 kg of hot water.
To kill bacteria, the water going into the tank at 20 °C must be heated to 60 °C.
Calculate the energy needed to increase the temperature of 100 kg of water by 40 °C.
Specific heat capacity of water = 4200 J/kg °C.…read more

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How many months each year will there not be enough solar energy to provide the hot
water used by an average European family?
.................................................. months
(1)
Power and electricity bills
Power is measured in watts (W) and it is the amount of energy transferred in one
second. So a 60W bulb transfers 60 Joules of energy every second.…read more

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So the bulb would then have used 0.3 kilowatt-hours of electrical energy.
Electricity companies charge you for every kilowatt-hour of electricity you use.
So, for example, if an electricity company changes you 10p per kilowatt-hour of
electricity used then the bulb has cost you:
Generating Electricity
The way electricity is generated is by
burning fuels to heat water. This
water then turns to steam (1). The
steam then spins the turbine (2)
which is connected to a generator (3).…read more