physics magnetism

magnetically soft material is…

• easy to magnetise

• easily to lose magnetism

• temporarily magnetised

magnetically hard material is…

• hard to magnetise

• hard to lose magnetism

• permanently magnetised

magnetic field is…

the region around a magnet where a force acts on another magnet/on magnetic material e.g. iron, steel, cobalt, nickel

strength of magnetic field is shown by…

spacing of magnetic field lines

• if closer together, field is strong

  • if far apart, field is weak

magnetic materials are…

materials which are always attracted by magnets, regardless of the pole

• they do not have to be magnets themselves

magnetic metals:

• iron

• cobalt

• nickel

• steel (alloy containing iron)

test for magnet:

if it can be repelled by known magnet

• if it can only be attracted, not repelled, it is magnetic material

permanent magnets

made out of permanent magnetic materials

• will produce its own magnetic field

• will not lose magnetism

induced magnets

• magnetism induced when magnetic material placed in magnetic field

• will lose most/all magnetism once removed from field

experiment investigating magnetic field pattern

1. place permanent magnet on piece of paper

2. draw dot at one end of magnet near corner (north pole)

3. place plotting compass next to dot, so that one end of the needle of the compass points away from the dot

4. use pencil to draw new dot at other side of compass needle

5. move compass so it points away from new dot, repeat process

6. keep repeating until there is a chain of dots going from one end of the magnet to the other

7. remove the compass, link the dots using a smooth curve - this is the magnetic field line

8. repeat the whole process several times to create other field lines

9. repeat whole process for two bar magnets placed 5cm apart first facing the same pole, then facing opposite poles

magnetic field is produced (around a wire) when…

a current flows through a conducting wire

right hand thumb rule

• used to work out direction of magnetic field

  • thumb points along direction of current, other fingers give direction

factors affecting field strength

• size of current

• distance from long straight conductor e.g wire - greater dist = weaker magnetic field

motor effect:

occurs when a wire with current flowing through is placed in a magnetic field and experiences a force

• effect = result of two interacting magnetic fields

  • result = wire will experience a force

DC motor

force on a current carrying coil is used to make it rotate in a single direction

consists of:

• coil of wire (free to rotate) - positioned in uniform magnetic field

• when horizontal, wire forms complete circuit with a cell

• coil attached to split-ring (circular tube of metal split in two)

• split right connected in a circuit with cell via contact with conducting carbon brushes

loudspeaker:

• converts electrical signals into sound

• consists of coil of wire wrapped around one pole of a permanent magnet

  1. AC passes through coil, creating changing magnetic field around coil

  2. direction of magnetic field constantly changing with current

  3. magnetic field produced around coil interacts with field of permanent magnet

  4. interacting fields exert force on coil

  5. force exerted on coil constantly changing direction, making coil oscillate

  6. oscillating coil causes speaker cone to oscillate, making air oscillate, creating sound waves

factors affecting magnetic force

• use stronger magnets

• increase amount of current flowing through wire

• place wire at 90 degrees to direction of pole’s magnetic field lines (maximum interaction bewteen fields)

Fleming’s LH rule

thumb - thrust/force

first finger - field line direction

second finger - current direction

electromagnet:

ONLY WHEN CURRENT IS FLOWING THRU WIRE

EM induction

A voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it