An investigation into the theory of resistance

Authors Avatar
An investigation into the theory of resistance

Resistance of a wire

An electric current is the flow of electrons through a material. The

Current through a wire is proportional to the potential difference

across it. Plotting a graph of P.D against current would give a

straight line graph through the origin.

P.D

(V)

[image002.jpg] I (A)

The gradient of the line (V/ I) is a constant and is called

resistance. Resistance is measured in ohms (Ohm).

The graph above is an ideal case where there is no temperature change

of the wire during the time that measurements are being taken. This

will not be the case as passing an electric current through a wire

causes it to heat up, as in an electric kettle or electric fire.

By setting the following circuit it is possible to determine the

resistance of a wire:

[image004.jpg] ( [image006.jpg] = wire sample)

Planning

I shall apply an electrical current through a piece of wire one

hundred centimeters long. I will be taking readings of current and

P.d. every 10 centimeters. With the information I gather, I will then

be able to calculate the resistance using the formula:

Voltage (V)

= resistance

(Ohm)

Current (I)

Aim

I aim to carry out an experiment which will enable me to show a

relationship between length of a wire and resistance of a wire. In

this investigation I will see how resistance of a wire varies with the

extending length. The things I could change in this experiment are

called the variables, these are:

- Material of the wire

- Width of the wire

- Starting temperature of the wire

- Current in the circuit

Prediction

I predict that as I take my readings moving further along the wire,

the greater the resistance will become. This is because the longer the

wire, the more times the free electrons will collide with other

electrons, such as the particles making up the metal. From this more

electrical energy should be transferred into thermal energy. This in

short, means less electricity can pass through the wire giving it a

greater resistance. If my prediction appears to be correct then the

results of the resistance against length graph will be directly

proportional and show positive correlation.

Here is a simple diagram showing a metal wire that shall be used:
Join now!


[image008.jpg]

It is the interaction between these positive atoms that causes the

wire to have resistance.

The inside of the metal has a regular array of positive ions (+ve);

this is when an ion is a metal atom, which has lost its free

electrons. The free electrons can swim about in the space between the

ions like gas molecules. When voltage is applied across the ends of a

wire the negative ions, (-ve) electrons, are attached towards the

positive end of the wire and current flows. Longer wires will cause ...

This is a preview of the whole essay