WJEC GCSE Physics 2 Electricity and Electrical Safety Revision Notes

Sorry about the last page.. not sure how much sense it makes (about ring mains/ domestic voltage etc.)

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  • Created on: 19-05-12 15:27
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Physics Revision Notes:
Electricity
Electrical Components:
Voltmeters and Ammeters:
Voltmeters measure the potential difference across a component in an electrical circuit; this means they
measure the voltage the component uses. Voltmeters therefore need to be placed in parallel. This means
they are not in the same `loop' as the component that they are measuring. This is shown on the diagram
below:
Ammeters measure the current flowing through a circuit; the
current is equal both just before the battery/ cell and just
after it, but can vary in a parallel circuit, depending on the
components placed on each different `loop'. Ammeters are
measured in series, meaning they are measured in the same
`loop' as components. The circuit to the right shows one lamp
in each `loop', and the current (I) would therefore split
equally between them. However, if there were two lamps in
one of the circuits, the current would split in a 2:1 ratio.
Current, Voltage and Resistance;
Current (I) - this is the measurement of how much electrical charge flows through a circuit, current can be
decreased by increased resistance. This is measured in amps.
Voltage (V) - Voltage measures the difference in electrical energy over a component, thus measuring the
voltage used by the component; this is measured in volts. It is not affected by resistance
Resistance ()- This is the resistance from the current to flow through the circuit. If a thin wire is used, the
resistance will be increased and less current will flow through the circuit. This is measured in Ohms ()
Resistance= Voltage
Current

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Changes in Current and Voltage:
Current change with a resistor- If the resistance on a variable resistor is increased, less
electricity will be able to flow, and therefore the current will be lower. The voltage flowing
across a variable resistor, is directly proportional to the current flowing through it.
Current change with a lamp- the resistance of a filament lamp increases as the temperature of its
filament increases.…read more

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Finding the correct fuse rating-
Current (amps)= Power (watts)/ Voltage (Volts)
Voltage from mains supply is 230 V; the power is on the appliance (will be given in an exam
question); to choose the correct fuse rating, the current in the fuse must be slightly higher than that in the
appliance.
M.c.b.…read more

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Mains electricity:
Different countries have a different mains voltage; however, the voltage for a domestic house in Britain is
approximately 230V; if the voltage as much higher than this, it can be extremely dangerous if there is a
fault. If the voltage was lower, it would cost more to step it up and down, also, more would be lost in the
wires.
This is the wiring in a main ring in a house;
there is usually one of these upstairs and
another one downstairs.…read more

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