SP12 - Magnetism and the Motor Effect ✓ Flashcards Preview

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Flashcards in SP12 - Magnetism and the Motor Effect ✓ Deck (26)
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SP12a - What is a permanent magnet?

A magnet that always has a magnetic field


SP12a - What is a temporary magnet?

A magnet material that only has a magnetic field when in the field of another magnet.


SP12a -When a temporary magnet enter a magnetic field and becomes magnetised, what can you say it is?

It is now an induced magnet


SP12a - What are the four magnetic materials?

  • Iron
  • Steel
  • Nickel
  • Cobalt


SP12a - What piece of equipment can be used to find the magnetic field of a bar magnet?

A plotting compass


SP12a - What do two opposite parallel magnetic plates create?

A uniform parallel magntic field


SP12a - What do the field lines aorund a bar magnet look?

  • They are going form north to south, increasingly spaced out the further away from the magnet.
  • They go in curves around the outside


SP12a - How do we know that the earth has a magnetic core?

  • It has field lines similar to that of a bar magnet around it.
  • We can see this through compasses.
  • It is a core made of nickel and iron.


SP12a - What is the key thing to remember about the earth's poles?

Its geographic north pole is its magnetic south pole and vice versa


SP12b - What does the direction of the magnetic field around a wire depend on?

The direction of the current


SP12b - What can we use to figure out the direction of the current and how can this be done?

  • Curl your right hand into a fist and stick out your thumb.
  • Point your thumb in the direction of the current and the direction your finger curl aorund is the direction of the magnetic field?


SP12b - When a magnetic field is shown what does a cross or a dot represent?

  • Cross means that the current is haeding away from you
  • Dot means the current is going towards you


SP12b - What is he shape of a magnetic field around a wire?



SP12b - When you coil a wire, what is it called?

A solenoid


SP12b - The magnetic field of a solenoid is similar to that of _______

A bar magnet


SP12b - What is the magnetic fieldat the centre of the solenoid similar to?

A uniform parallel field


SP12b - What do you call a solenoid with a current flowing thorugh it?

An electromagnet


SP12b - What are the ways you can make an electromagnet stronger?

  • Adding an iron core (a temporary magnet)
  • Increasing the current


SP12b - What is the strength of the magnetic field around a wire dependant on?

  • The strength of the current (Stronger when higher)
  • The distance from the wire (stronger when closer)


SP12c - When does the motor effect occur?

When a wire carrying a current enters a uniform parallel magnetic field


SP12c - Why does the motor effect occur and what does it produce?

The magnetic field from the wire acting against the magnetic field from the uniform parallel field produces a force that acts on the wire.


SP12c - What can be used to work out the direction of the force in the motor effect?

The left hand rule:

  • Set your hand so your thumb is up and your first and second fingers are at right angles.
  • Your first finger represents the direction of the field.
  • Your second finger represents the direction of the current.
  • Once these are lined up, the way your thumb is pointing will be direction of the force


SP12c - How do you calculate the force exerted on a wire in the motor effect.

F = B I L

Force (N) =

Magnetic field strength (T) x Current (A) x Length of wire inside the UP field (m)


SP12c - What are the two units and the alternate name for magnetic field strength?

Magnetic flux density:

  • T - Telsa
  • N/Am - Newton per amp metre


SP12c - How do motors spin?

  • The motor effect is set up so that the wire returns back to where is started.
  • This means there are two sections of the wire inside the UP field with current travelling in different directions in each.
  • This means that the direction of force on one will be up and down on the other.
  • The wires are centered around a pivot which allows these forces to cause a turning motion.
  • This is the motor effect.


SP12c - What is a split - ring commutator used for?

  • Once the side of the motor's wire that is moving upwards has made a half turn it will be on the other side but still experiencing an upward force.
  • This would mean that the motor keeps spinning back and forth around that point without ever making a full turn.
  • The SR commutator means that once it has made a half turn the current will be 'reset' and change direction so the wire that was previously having a current going forward will now have it going back.
  • So the wire experiencing an upward force will now experience a downward force and vice versa.