Magnets

Attraction & repulsion

when 2 magnets are brought close together they exert a force on each other either attraction/repulsion

magnetic material

• attract to both poles

• iron, cobalt, nickel

• steel → an alloy

• iron+carbon

What does a magnetic compass contain

• a small bar magnet

• the earth has a magnetic field

• the compass needle points in the direction of the magnetic field of that region

magnetic field

the region around a magnet where a force acts on another magnet

Why is a magnetic field useful for Earth?

it’s vital for life on earth as it deflects harmful solar radiation & cosmic rays

What is a permanent magnet?

• a magnet that produces its own magnetic field so its always magnetic like a bar magnet

• often made from iron

• the further the field lines the weaker the field

• field lines closer together the stronger the magnetic field

• → strongest at the poles

electromagnet

a magnet that can be turned on and off

How does an electromagnet turn on and off

• when an electrical current flows through a wire it creates a magnetic field

• when the current is turned off the magnetic field disappears

What does the pattern of the magnetic field around a wire with a current flowing through look like?

concentric circles

• increasing the current increases field strength

• closer to the wire the field gets stronger

• if direction of current changes the direction of the field does too

induced magnet

A temporary magnet, made from a magnetic material placed in a magnetic field. The induced magnetism is lost when moved out of the magnetic field.

solenoid

magnetic field produced by a current flowing through a coiled wire

produces a much stronger magnetic field than a straight wire

similar to a permanent magnet and magnetic wire

How is an electromagnet made

an electromagnet is a solenoid with an iron core

• add iron core

• add more turns to coil

• increase the current

How does the iron core affect the electromagnet?

the iron core increases the strength of the magnetic field because the magnetic field created by the solenoid magnetises the iron bar

uses of electromagnetic devices

• make and break switch

• relay switch

• circuit breaker

make and break switch

Purpose: rapidly and repeatedly open and close an electrical current → creates a cycle of current flow

Uses: automates switching, creates repetitive motion of sound

relay switch

Purpose: acts as an electrically operated switch that uses a lower power signal to control a higher power circuit

Uses: cars and industrial machines

circuit breaker

Purpose: to automatically switch off the electrical current if certain conditions are reddened if its too high

How can magnetic fields can be mapped out using small plotting compasses

1. place the plotting compass near the magnet on a piece of paper

2. mark the direction the compass needle points

3. move the plotting compass to many different positions in the magnetic field, marking the needle direction each time

4. join the points to show the field lines