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Module 2.2 resistance
Electromotive force
Electromotive force (e.m.f) ­ This is the energy transferred per unit of charge when one
other type of energy is converted into electrical energy
To find an electrical current you need to know how much energy is supplied to each unit of
charge. This is called the e.m.f. This can be represented in equation form:
Electromotive F orce (V ) = Electrical energy transferred (J )
charge (C)
e.m.…read more

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There are many different Electrical Abbreviations that are used.…read more

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Resistance and Ohms Law
Ohms Law
Ohms law is a law of physics discovered in the 1820s by German Physicist George Ohm. It states that
by increasing the number of cells in a battery connected to a length of wire produced a
proportionate increase in the current flowing through the wire, providing the temperature stayed
the same. He then published his own law called Ohms Law
Ohms Law ­ The current through a conductor is proportional to the potential difference across it.…read more

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The V-I characteristics of a Light emitting Diode (LED)
I diode is a simple device which lets current pass through it in 1 direction only. They can have
a large current pass through them and special ones called LED's emit light when they have
current passing through them. Advantages are:
Switch on instantly
Are very robust
Are very versatile
Operate on low P.ds
Have a long working life
As they are becoming better and better they are being used
more and more.…read more

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The effect of temperature on restivity
Variation of resistance of a metal with temperature
The internal energy in atoms increases with temperature. As long as a material does not
melt then its volume will remain unchanged. There is also no change in potential energy,
however there is a change in kinetic energy caused by the vibrations of the individual atoms.
This in itself results in an increase in the resistance of the material.…read more

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Domestic electrical supply
Domestic house electricity is supplied at 230V and a current of up to 60A. This means the
maximum power that can be used at any time is 13.8Kw. The current is supplied to the
house by distribution boards. They instantly activate if there is an overload of current in a
circuit protecting it. They can be reset when the problem has been alleviated.
Plugs attached to appliances such as TVs, computers and hairdryers also have Fuses in them
which prevent overloading.…read more

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