Physics - 15 Electromagnetism - 15.1 Magnetic Fields & 15.2 Magnetic Fields of Electric Currents & 15.3 Electromagnets in Devices

Pole

end of a magnet where the magnetic force is maximum

The south pole of a magnet is generally (positive/negative)

positive

The north pole of a magnet is generally (positive/negative)

negative

Magnetic field lines point from ...

north to south

North-seeking

points towards the north pole when suspended freely

South-seeking

points towards the south pole when suspended freely

Magnetic field

area around a magnet where magnetic influence is felt

Magnetic metals [3]

- iron

- cobalt

- nickel

Magnetic field line

lines of force in a magnetic field

Magnetic domain

grouping of atoms that have their magnetic fields aligned

Permanent magnet

magnet made of material that keeps its magnetism

Magnetise

make into a magnet by aligning magnetic domains

Demagnetise

remove magnetic properties from a magnet

Why is steel used for permanent magnets?

magnetised steel retains its magnetism

Induced magnetism

when a magnetic material (usually iron) becomes temporarily magnetised in the presence of a magnetic field

What does it mean for a magnetic material to be 'hard'?

it doesn't easily lose its magnetism

When a current passes through a wire ...

a magnetic field is set up around the wire

What shape are the magnetic field lines caused by a straight current-carrying wire?

concentric circles

Right-hand rule [2]

- thumb defines direction of current

- fingers define direction of magnetic field

Current exiting page

circle with dot, representing tip of arrow, labelled with I

Current entering page

circle with cross, representing shaft of arrow, labelled with I

Solenoid

coil of insulated wire

If the current is increased, the magnetic field strength will (increase/decrease)

increase

If the number of turns in the coil is increased, the magnetic field strength will (increase/decrease)

increase

How to describe the field lines inside a solenoid [2]

- parallel to the solenoid's axis

- in a uniform direction

Electromagnet

solenoid in which the wire is wrapped around an iron core

Uses of electromagnets [4]

- scrapyard crane

- circuit breaker

- electric bell

- relay

Scrapyard crane [2]

- powerful electromagnets lift steel vehicles when a current flows through them

- drop them when the current stops

Circuit breaker [3]

- a circuit contains both a switch and an electromagnet

- if a current that is too high flows, the electromagnet increases in strength

- it then pulls the switch open, stopping the current

Electric bell [5]

- when a current flows, electromagnet activates

- attracts iron armature, which strikes bell

- iron armature disconnects from contact, stopping current

- electromagnet deactivates and armature returns to contact

- current flows again

Relay [4]

- current flows in a small circuit, activating an electromagnet

- electromagnet attracts a switch attached to a spring

- switch touches contact, allowing current to flow in larger circuit

- when electromagnet is deactivated, spring pulls switch back to rest