P9: The strength of an electromagnet - CCEA

To investigate, describe and recall how the strength of the magnetic field depends on the current in the coil, the number of turns in the coil and the material used as the core of the coil.

The main variables in a science experiment are the independent variable, the dependent variable and the control variables.

The independent variable is what we change or control in the experiment.

The dependent variable is what we are testing and will be measured in the experiment.

The control variables are what we keep the same during the experiment to make sure it’s a fair test.

What are the variables in prescribed practical P9?

In this experiment the:

• Independent variable is the current in the coil.

• Dependent variable is the strength of the electromagnet, indicated by the number of paper clips that the electromagnet can hold.

• Control variables are the material of the core, the number of turns of the electromagnet coil, size of paper clips.

Remember - these variables are controlled (or kept the same) because to make it a fair test, only 1 variable can be changed, which in this case is the current.

What is the prediction for this practical?

As the current increases, the electromagnet will get stronger and hold more paper clips.

What is the justification for this prediction?

The magnetic field is caused by the current flowing in the wire.

The bigger the current the stronger the magnetic field and hence the stronger the electromagnet.

What apparatus is needed to carry out prescribed practical P9?

1m length of insulated wire, iron nail, a variable low voltage power pack, an ammeter, connecting leads, a retort stand, a boss and clamp, 2 crocodile clips, paper clips.

1. Wind the insulated wire tightly around the nail to make an electromagnet.

2. Set up the equipment as shown in the diagram.

3. Adjust the power pack so that a current of 0.1 A flows. Record the current in a suitable table.

4. Attach as many paper clips to the electromagnet as it will hold. Count the number of paper clips and record in the table. Switch off the electromagnet.

5. Switch on again. Check that the current is still 0.1 A and repeat the paper clip reading. Record in the table and calculate the average number of paper clips held.

6. Repeat this process increasing the current by 0.1 A up to 0.6 A.

Error

Ensure that the paper clips are the same size and material.

They should not be too big.

How to record the results of this practical

Graph

As the current increases the number of paper clips held also increases.

This means that the strength of the electromagnet increases with increasing current, which agrees with our prediction.

In fact, since the line of best fit is a straight line through the origin, we can be even more precise.

We can say that, the strength of the electromagnet is directly proportional to the current.

If you double the current, you double the strength of the electromagnet.