GCSE Science | Electromagnetism

Electromagnetism

• Whenever there is wire with a current going through it
• there will be a (small) magnetic field around it

Right hand rule

• thumb is the current
• fingers are the magnetic field

How to increase the size of the magnetic field around a wire

• increase the current
• coil the wire
• add an iron core

Solenoid

• coil of wire (current on)
• with an iron core
• same magnetic field lines as that of a bar magnet

Motor effect

• a current-carrying wire will produce a small magnetic field
• if you place this wire between permanent magnets,
• the magnetic fields will interact
• this will create a force causing the wire will spin
• we can add a split-ring commutator which will reverse the direction of the current at every half-turn to allow the coil to keep rotating

Fleming's left hand rule

• this rule can be used to determine the direction the wire will spin in
• first finger - field (north to south)
• second finger - current
• thumb - movement (force)

How to increase the force from the motor effect

• increase the length of the wire
• increase the current
• use stronger magnets/ move the magnets closer

Triple Science Only

Loudspeakers

• same as motor effect
• no split-ring commutator
• changing force leads to pressure variations
• which is interpreted as sound

How is potential difference induced?

• constantly move magnets through a wire
• constantly move a wire through a magnetic field
• a current will also be induced if the potential difference is connected to a complete circuit

Factors affecting the size of induced potential difference

• stronger magnetic field
• move the wire or magnet through faster
• coil the wire

Generator effect (moving coil)

• Coil is rotated within a magnetic field
• As it turns the coil cuts the magnetic field lines.
• This induces a voltage (or current) in the coil.
• This can then be connected to an existing circuit.
• In a generator, energy is being converted from kinetic (mechanical) energy into electrical energy.
  • The size of the induced voltage (or current) can be increased by:
    • Using a stronger magnet
    • Having more turns in the coil
    • Spinning/moving the coil faster.

Generator effect (moving wire)

• Magnet is rotated within a coil.
• As it turns the coil cuts the constantly changing magnetic field lines from the magnet.
• This induces a voltage (or current) in the coil.
• This can then be connected to an existing circuit.
• In a generator, energy is being converted from kinetic (mechanical) energy into electrical energy.
  • The size of the induced voltage (or current) can be increased by:
    • Using a stronger magnet
    • Having more turns in the coil
    • Spinning/moving the magnet faster.

Generator effect in a microphone

• A sound wave reaches the flexible diaphragm, causing it to vibrate.
• This moves the solenoid/coil of wire up and down.
• The solenoid/coil of wire cuts the permanent magnetic field.
• This induces an alternating potential difference
• and an alternating current as it is connected as a complete circuit.