SP12 - Magnetism and the Motor Effect ✓ Flashcards
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 around a magnet look like?
- 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 magnet field and how can this be done?
(GRIP RULE)
- 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 around 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?
Circular
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.
