MAGNETISM

magnetic field

region where magnetic force is exerted

what do magnetic field lines show

-what direction do they point

size and direction of magnetic fields

-ALWAYS NORTH TO SOUTH

what happens if place two permanent bar magnets of opposite poles near each other

a uniform field created

• closer the field lines = stronger the field

how can magnetism be induced?

• when magnetic material brought near magnet (into mag field), the material acts as a magnetic → induced

• the closer they get, the stronger the induced magnetism will be

name magnetic materials - 4

1. nickel

2. iron

3. cobalt

4. steel

• they have magnetic domains, which are randomly aligned and cancel out eachothers affects

→ but then domains align same direction, becoming magnetised

what is a soft and a hard magnetic material, example of both

soft - looses induced magnetism easily IRON

hard - keeps it permanently STEEL

use of soft magnetic material

IRON in TRANSFORMERS and ELECTROMAGNETS

→ can turn on and off quickly, magnetise and demagnetise

use of hard magnetic material

STEEL as FRIDGE MAGNET

how can u increase strength of mag field around solenoid?

added ‘soft iron core’ through middle of coil

how does a current carrying wire create a magnetic field, 3

1. an electric current in a conductor produces a magnetic field around it

2. larger the current → strong the field

3. direction of magnetic field depends on direction of current

what is the motor effect

when a current carrying wire is put between two magnetic poles, two magnetic fields affect one another

→ the result is a force on the wire, causing wire to move - motor effect

whats needed for motor effect

• wire must be 90 degree to magnetic field

→ if it runs along magnetic field, wont experience force

flemings left hand rule

thumb; motion (force)

pointer: field

middle; current

4 factors which speed up electric motor

1. more current

2. more turns on coil

3. stringer mag field

4. soft iron core

how does an electric motor work;

Current through the coil creates a temporary magnetic field around it. This magnetic field interacts with magnetic field between the two magnets.This results in a force on a coil.The force on opposite sides of coil is in opposite directions so the coil rotates. The split ring commutator swaps the contacts every half turn to keep the motor rotating in same direction.

how can u reverse direction of motor

swapping magnetic poles over

how do loudspeakers work;

current flows through coil, creating magnetic field around it. This magnetic field interacts with the magnetic field of the magnet. This produces a force on the coil. As the direction of alternating current changes, the direction of coil reverses → making coil move back and forth, coil attached to speaker which then moves forwards and backwards → vibration causes air particles to vibrate, generating sound wavw

what is electromagnetic induction;

creation of voltage in a wire which is experiencing a change in magnetic field

what is the use of electromagnetic induction

used to generate electricity from KE stores, is called dynamo effect

what are two different situations when u get electromagnetic induction;

1. an electrical conductor moves through magnetic field

2. magnetic field through an electrical conductor changes

how can u test for electromagnetic induction

connecting an ammeter to conductor, and moving it through field which will show mag and direction of induced current

• current induced because change in mag field lines induces a voltage

3 ways to get bigger voltage

1. strength of magnet

2. number of turns of coil

3. speed of movement

how do AC generators work;

• a motor

→ but instead of split ring commutator, have slip rings and brushes so contacts dont swap every half turn

→this means they can produce a.c voltage