Magnetic Force
Electricity and Magnetism

# The simplest motor

Practical Activity for 14-16

In this activity students build a simple motor. You can use it to illustrate Fleming's left hand rule.

## Apparatus

Each group of students will need:

• Neodymium magnet
• Screw
• Short length of cable with two bare ends
• 1.5 V cell

## Preparation and safety

Rare-earth magnets are brittle and shatter easily. Students should not lift the magnet too high off the bench.

## Preparation and safety

1. Put the head of the screw onto magnet so that they attach to each other.
2. Put the negative terminal of cell onto sharp end of screw so that it also attaches.
3. Lift assembly off the bench by gripping the cell so that there is a small gap between bench and magnet.
4. Hold one end of cable onto the top of cell and touch the other end to edge of the magnet. The magnet and screw should start to spin.

## Discussion prompts

• Which direction is the current in the magnet?
• Which direction is the force that makes it spin?
• Which direction is the magnetic field?

If students struggle to identify the direction of current, remind them it flows from the positive to the negative terminals of the cell. Inside the magnet the current is radially inwards from the edge to the centre.

To work out the direction of the force they can look at whether their magnet spins clockwise or anticlockwise. To work out the direction of the magnetic field they can use Fleming’s left hand rule. If the magnets spins anticlockwise the magnetic field is downwards, if it spins clockwise it is it upwards.

## Learning outcome

Students apply Fleming’s left hand rule to determine the direction of a magnetic field.

This experiment was safety-tested in March 2020.

###### Magnetic Force
appears in the relation F_mag=Bqvsinθ F_mag=BILsinθ