The following experiment was performed by a group of students as a practical investigation into electromagnets.

The apparatus was set up as shown in the diagram.

An iron nail was used as the core of the electromagnet.

Insulated wire was carefully wrapped around the nail to form the electromagnet coil.

How the strength of the electromagnet changed was found by comparing how many paperclips the electromagnet could pick up.

The paperclips were attached to form a chain of varying weights so that the strength of the electromagnet could be fairly assessed.

The number of turns of wire was kept constant while the current was varied and then the current was kept constant while the number of turns was varied.

Paper clips are made of steel - a hard magnetic material. Therefore the paperclip chains had obtained magnetic properties of their own after being picked up by the nail. It was necessary to drop them on the floor until the lost their magnetism between readings.

Ideally a 'soft iron' nail would be used - but the ones we were given by the technicians were found not to be as 'soft' as we would like. They retained a little magnetism after the current was switched off. We therefore tested them between measurements by trying to pick up paper clips with them with the current switched off. If they were still magnetic we 'dropped then on the floor' (being careful not to drop them on someone's foot!) between measurements.

Long chains of paperclips required lifting very high. We therefore opened a paperclip up and used it as a hook for little chains rather than have one long one.

To save time members of the group made little chains of five paperclips that could be used in the experiment.

Plot graphs to show how the number of paperclips picked up by the electromagnet varied with

1. the current flowing through the electromagnet
2. the number of turns of wire of the electromagnet

Use your graphs to describe any pattern or trend that you observe.