# Magnetism and electromagnetism in a nutshell

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IGCSE Magnetism and Electromagnetism in a Nutshell
1. A magnetic field line shows the direction of the force on a north pole
2. An electric current in a conductor produces a magnetic field round it. Know
the magnetic field patterns for a straight wire, a flat circular coil and a
solenoid when each is carrying a current
3. Electromagnets eg electric bell, relay, lifting magnet are constructed with a
solenoid wrapped around an iron core which is magnetised when current
flows. This attracts and move another soft iron bar which is pulled back by a
spring by when the current is switched off
4. When a wire carrying current is at right angles to a magnetic field a force is
exerted on it that is at right angles to the field and the current which makes it
move. The direction of the resulting force when a wire carries a current
perpendicular to a magnetic field is predicted using Fleming's Left Hand rule
5. When current flows through a coil in a magnetic field opposite direction
forces act on opposite currents cause it to rotate
6. The coil continues to rotate since a split ring commutator reverses the current
every half turn
7. Motors can be made more powerful by using a large current, a stronger
magnet, wrapping the coil round an iron core
8. The motor effect explains how loudspeakers work
9. A voltage is induced in a conductor when it moves through a magnetic field or
when a magnetic field changes through a coil; This is electromagnetic
induction
10. If a coil is rotated using a turbine and the battery replaced by a bulb,
electricity is generated and the bulb lights. The motor is now a generator
11. A transformer consists of 2 coils wrapped round a laminated iron ring
12. The primary coil is an ac electromagnet, which passes an alternating magnetic
field through the iron to the secondary coil inducing a voltage by
electromagnetic induction
13. Applications of electromagnetic induction include: dynamo, generator,
flow-meter, microphone