Electromagnetism — Part 1: Magnetic effect of a current: visual lesson, ICSE Class 10 Physics (Science Paper 1)

Lesson

Electricity that behaves like a magnet

Part 1 — a wire carrying current is surrounded by a magnetic field. Coils of wire make electromagnets, and a magnet can push on a wire that carries current.

In this lesson you will

Describe Oersted’s experiment and draw the field of a straight wire and a loop
Use the right-hand thumb rule to find the direction of a magnetic field
Describe a solenoid and an electromagnet; list ways to make an electromagnet stronger
Use Fleming’s left-hand rule and name the parts of a DC motor and its energy conversion

Table of devices that use the magnetic effect of an electric current
Device	Uses the magnetic effect of current by
Electric bell	An electromagnet pulls an iron striker
Crane in a scrapyard	A large electromagnet lifts iron
Ceiling fan	A motor: force on coils in a magnetic field
Loudspeaker	Force on a coil makes a cone vibrate

Diagram

Oersted’s experiment

In 1820 Hans Christian Oersted placed a compass needle just below a wire stretched along the north–south line. With no current, the needle pointed north along the wire. When a current flowed, the needle was deflected; reversing the current reversed the deflection. Conclusion: an electric current produces a magnetic field around it.

Diagram

Field of a straight wire; the right-hand thumb rule

The field lines round a long straight wire are concentric circles centred on the wire, in a plane at right angles to it. The field is stronger close to the wire and stronger for a larger current. Right-hand thumb rule: hold the wire in the right hand with the thumb along the current; the curled fingers show the direction of the field lines.

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