Resistance of a Wire Experiment

Resistance of a Wire Experiment

Task

To investigate how the resistance of a wire is affected by the length

of the wire.

Theory

What is resistance?

Electricity is conducted through a conductor, in this case wire, by

means of free electrons. The number of free electrons depends on the

material and more free electrons means a better conductor, i.e. it has

less resistance. For example, gold has more free electrons than iron

and, as a result, it is a better conductor. The free electrons are

given energy and as a result move and collide with neighbouring free

electrons. This happens across the length of the wire and thus

electricity is conducted. Resistance is the result of energy loss as

heat. It involves collisions between the free electrons and the fixed

particles of the metal, other free electrons and impurities. These

collisions convert some of the energy that the free electrons are

carrying into heat.

How is it measured?

The resistance of a length of wire is calculated by measuring the

current present in the circuit (in series) and the voltage across the

wire (in parallel). These measurements are then applied to this

formula:

V = I ´ R where V = Voltage, I = Current and R = Resistance

This can be rearranged to:

R = V

I

Ohm's Law

It is also relevant to know of Ohm's Law, which states that the

current through a metallic conductor (e.g. wire) at a constant

temperature is proportional to the potential difference (voltage).

Therefore V ¸ I is constant. This means that the resistance of a

metallic conductor is constant providing that the temperature also

remains constant. Furthermore, the resistance of a metal increases as

its temperature increases. This is because at higher temperatures, the

particles of the conductor are moving around more quickly, thus

increasing the likelihood of collisions with the free electrons.

Variables

Input:

· Length of wire. *