Magnetic Force
Electricity and Magnetism

# Magnetic methods

Practical Activity for 11-14 14-16

In this activity, students try out different ways to find the strongest magnet. You can use it to develop experimental skills.

## Preparation

This is an ideal opportunity to use old magnets that may be lurking in your prep room.

## Equipment

Each pair of students will need:

• Two weak magnets
• Plotting compass
• Ruler
• Several paper clips
• A pin

## Procedure

Ask students to try four methods for comparing the strength of magnets:

1. Hang paper clips from one end of each magnet. How many can it hold?
2. Movie one magnet downwards towards a pin on a table to see how close it needs to be to lift it off the table. Repeat with other magnet.
3. Place a compass on the table so that its needle pointing north. Then place the two magnets symmetrically on opposite sides of the compass. Which way does the compass turn?
4. Move a magnet towards the compass and measure the distance at which the needle deflects through 45˚. Repeat with other magnet.

## Discussion prompts

• How do you know which magnet is strongest?
• Which of the four methods is most reliable?
• Can you devise a method of your own to compare the strength of your magnets?

## Teaching notes

Most experimental methods taught at secondary school have been carefully refined over the years to be reliable. This activity is designed to encourage students to explore experimental design in a more open ended way. At the start the activity, you could provide diagrams as an aid:

To test which method is most reliable they could repeat maesurements. Method 1 is a very crude and insensitive technique. Method 2 introduces an element of measurement. Method 3 provides an opportunity to discuss fair testing (the magnets need to be placed symmetrically). In method 4 the angle chosen is arbitrary. Alternatives would be the distance at which compass needle turns through eg 30˚ or to measure the angle when the magnet is at 10 cm (or other fixed distance) from the compass.

## Learning outcome

Students design an experiment for comparing the strength of two magnets.

This experiment was safety-checked in March 2020.