Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire.

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Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire.
These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how
hard it is to move the electrons through the wire.

Resistance is measured in Ohms. This was the scientist who discovered resistance.  Ohm created a law, and called it Ohm’s Law.

“Ohm's Law deals with the relationship between voltage and current in a metallic conductor.”

This relationship states that

“The potential difference (voltage) across an ideal conductor is proportional to the current through it.”

Current (I): is the result of electrical charges on the move. This charge is more than often carried by the negative electrons.  For the current to flow there must be a continuous pathway between the terminals of the power supply. Current is calculated using a device called a Ammeter and is measured in amperes (A)

Voltage (V) (also known a Potential Difference. p.d)

The Potential Difference is the energy transferred to other forms per unit charge. So, in a series circuit the voltage (p.d) may be found by adding the voltage across the separate components e.g. bulbs. Voltage is calculated using a device called a Voltmeter. Voltage is measured in Volts (V)

Mathematical treatment of Ohm’s Law.

Resistance (ohms) = voltage (in V)

                                   current (in A)

We can work out any one of the factors, as long as we have the other two.

This can be shown in the triangle below.

The equation, in terms of energy can be shown like this

Electric energy             Kinetic energy             Heat energy


There are different factors that affect the resistance on a wire. Here are some of them.

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1.Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their
increase in energy. This causes more collisions between the electrons and the atoms as
the atoms are moving into the path of the electrons. This increase in collisions means that
there will be an increase in resistance.


2.Material: The type of material will affect the amount of free electrons, which are able to flow through
the wire. If the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.


3.Wire length: If the length of the wire is ...

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