Interactive practical

Electromagnet strength

Wind a coil on a core and count the paperclips it picks up as you change the current, the number of turns and the core material.

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GCSE Physics

Investigating an electromagnet

CCEA 1210 — matched to your course.

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Practical focuses1

Questions available2

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Available question marks4

Practical focus

Investigate how current, coil turns or core material affect the strength of an electromagnet using a controlled low-voltage circuit.

Practical method

Aim

Investigate how the number of turns of wire on a coil affects the strength of an electromagnet.

Variables

Independent variable: number of turns on the coil
Dependent variable: number of paperclips picked up
Control variables: current (adjusted with a variable resistor); the same iron core; the same size paperclips.

Apparatus

Iron nail (core)
Insulated wire
Low-voltage power supply
Ammeter
Variable resistor
Switch
Paperclips

Method

Wrap 10 turns of insulated wire around an iron nail and connect it in series with an ammeter, variable resistor, switch and power supply.
Close the switch and adjust the variable resistor so the current is 1.0 A.
Dip the nail into a pile of paperclips, lift it, and count the clips held.
Switch off and remove the clips. Repeat three times and find the mean.
Repeat for 20, 30 and 40 turns, keeping the current at 1.0 A.
Plot the mean number of paperclips against the number of turns.

Sample results

Iron nail core, current kept at 1.0 A.

Number of turns	Mean paperclips held
10	4
20	8
30	13
40	17

Analysis

The number of paperclips increases roughly in proportion to the number of turns: doubling the turns from 10 to 20 doubles the clips from 4 to 8. More turns give a stronger magnetic field. Increasing the current or adding an iron core also increases the strength.

Errors and improvements

Problem	Effect	Improvement
Paperclips are a coarse measure	Low resolution; results vary	Use smaller clips or measure the field with a magnetometer/balance
Current changes as the wire warms	Unfair test	Adjust the variable resistor to keep 1.0 A
Core stays slightly magnetised	Later readings too high	Use a soft iron core and tap it between runs

Risk assessment

Hazard	Risk	Control measure
Coil and wire get hot	Burns	Keep current low and switch off between readings
Paperclips flying off	Minor injury	Keep faces away; do not use too high a current

Common mistakes

Changing the current along with the number of turns.
Using a steel core that stays magnetised.
Not taking repeat readings with a discrete measure like paperclips.

Worked analysis

Repeats for 30 turns: 12, 14 and 13 clips. Mean = (12 + 14 + 13) ÷ 3 = 13 clips.

Common misconception

An electromagnet only works while current flows; the magnetic field is produced by the current, not stored in the wire.

Variations required by some exam boards

Changing the core material (CCEA): keep the number of turns and the current fixed and compare an iron core, a steel core, an aluminium core and no core (air). Iron gives the strongest electromagnet; aluminium is not magnetic and gives about the same result as air. Core material is a categoric variable, so present the results as a bar chart.

Changing the current: keep the number of turns fixed and use the variable resistor to set currents of 0.5–2.0 A; the strength increases with current.

Assessment coverage

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2 questions available, worth 4 marks in total.

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