Electromagnetism
Revise Electromagnetism for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A current-carrying wire produces a magnetic field, and a solenoid concentrates this field to behave like a bar magnet.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
When a current flows through a conducting wire, a magnetic field is produced around it. This is electromagnetism.
The shape of the field is a series of concentric circles with the wire at the centre, in a plane perpendicular to the wire. The strength of the field depends on the current and on the distance from the wire — a larger current or a smaller distance gives a stronger field.
Shaping the wire into a solenoid increases the field strength, because the fields from the individual turns add together. The field inside a solenoid is strong and uniform, and outside it the field is like that of a bar magnet. Adding an iron core strengthens it further, producing an electromagnet.
Revision notes
The field around a wire
A current-carrying wire produces a magnetic field around it.
The field consists of concentric circles centred on the wire, in a plane perpendicular to it. Reversing the current direction reverses the field direction.
Factors affecting strength
The field is stronger when the current is larger.
The field is weaker further from the wire. Both relationships are examinable and often appear together.
Solenoids and electromagnets
Shaping the wire into a solenoid increases the field strength, because the fields from individual turns add together.
The field inside a solenoid is strong and uniform; outside it resembles a bar magnet. Adding an iron core makes it much stronger still, producing an electromagnet that can be switched on and off.
Key points
- A current-carrying wire produces a magnetic field.
- The field is concentric circles around the wire.
- A larger current gives a stronger field.
- The field weakens with distance from the wire.
- A solenoid increases the field strength.
- An iron core makes an electromagnet.
Worked examples
Example 1
Describe the shape of the magnetic field around a straight current-carrying wire. [2 marks]
Model answer
It consists of concentric circles centred on the wire (1 mark), in a plane perpendicular to the wire (1 mark).
Example 2
State two ways to increase the strength of the magnetic field produced by a solenoid. [2 marks]
Model answer
Increase the current flowing through it (1 mark). Add an iron core, or increase the number of turns of wire (1 mark).
Example 3
Explain why a solenoid produces a stronger field than a single straight wire. [2 marks]
Model answer
A solenoid has many turns of wire close together (1 mark), and the magnetic fields from the individual turns add together to give a stronger overall field (1 mark).
Common mistakes
Drawing the field as straight lines along the wire.
It is concentric circles around the wire, perpendicular to it.
Saying the field strengthens with distance.
It weakens as distance from the wire increases.
Forgetting the iron core.
It is what turns a solenoid into a much stronger electromagnet.
Saying the field inside a solenoid is weak.
It is strong and uniform inside.
Exam tips
- Describe the field shape as concentric circles.
- Give both current and distance as factors.
- Explain the solenoid through fields adding.
- Name the iron core when describing an electromagnet.
Key terms
- Solenoid
- A coil of wire producing a magnetic field.
- Electromagnet
- A solenoid with an iron core.
- Concentric
- Sharing the same centre.
- Uniform field
- A field of constant strength and direction.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.