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igcse physics notesprinted 98 · PDF 98
124 pagesrevision 46936
printed 98 · PDF 98
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98
Electromotive force:
The electromotive force (e.m.f) of an electrical source of energy is
measured in volts and is the
energy supplied by the source per unit charge in driving the charge round a
complete circuit.
Formula: work done on charge/charge(J/Q)
V= J/Q
Potential difference:
Potential difference V is measured in volts (1 V = 1 JC-1) and is the work
done per unit charge in moving between two points in a circuit or through a
component.
● It is measured with a voltmeter placed in parallel across the component.
● The higher the potential difference, the greater the current
Formula: work done by charge/charge
V= J/Q
Resistance:
The resistance of a component is the ratio of the potential difference
through a component and current flowing through it. It is measured in
ohms. The greater the resistance, the harder it is for current to flow through
the component.
● As the length of a resistor increases, the resistance increases. The
resistance is directly proportional to the length.
● As the diameter of a resistor increases, the resistance decreases. The
resistance is inversely proportional to the cross-sectional area.
Formula: potential difference/current
R=V/I