Magnetism and Electromagnetism Flashcards
Do like poles attract or repel?
Repel
Do unlike poles attract or repel?
Attract
What are magnetic materials?
Materials that are attracted to magnets and can be magnetised
eg iron, steel, cobalt, nickel
What are non-magnetic materials?
Materials that are not attracted to magnets and cannot be magnetised (eg glass, plastic)
What are magnetically hard and soft materials?
Hard: can be permanently magnetised, eg steel
Soft: can only be temporarily magnetised, eg soft iron
How can you induce magnetism?
By placing a magnetic material in a magnetic field (near to a magnet)
The closer to the magnet, the stronger the induced magnetism
What is a magnetic field?
An area where magnetic materials experience a force.
Rules for drawing magnetic field lines:
Arrows pointing north to south
Continuous
Non-crossing
Line density = magnitude of force
Using iron filings to show magnetic field patterns:
Place magnet(s) under a piece of paper
Scatter over iron filings
Tap the paper until the iron filings show a clear pattern
How does current create a field?
An electric current passing through a conductor produces a magnetic field around it
Right hand grip rule
How are electromagnets constructed?
Current-carrying insulated solenoid with iron core inside creates magnetic field, like field produced by bar magnets
What is the motor effect?
When a current-carrying conductor is perpendicular to a magnetic field, a force is exerted.
Left hand rule
What is Fleming’s left hand rule?
thuMb - Motion
First Finger Field
seCond - Current
How do loud speakers work?
Coil attached to cone in magnetic field
AC flows through coil, cone is pushed away and pulled back, vibrations produce sound.
How do DC motors work?
Coil of wire between two permanent magnets
DC flows in opposite direction on each side of coil, creates turning effect
Split ring commutator used to ensure current direction reverses every half term
Carbon brushes
How can you increase the magnitude of a force due to the motor effect?
Increase magnitude of current
Increase magnetic field strength
What is electromagnetic induction? (aka generator effect)
The induction of voltage when a current-carrying conductor is moved through a magnetic field.
How can you increase the induced voltage?
Moving the wire more quickly
Using a stronger magnetic field
Increasing the length of wire
How do AC generators work?
Coil is rotated in a magnetic field
Current induced in coil, changes direction every half-turn
Slip ring commutators
What is a transformer?
Two different sized coils wrapped around a soft iron core
Changes the size of the voltage of an alternating current
Step-up vs step-down transformers
Step-up: increases voltage, secondary coil has more turns than primary
Step-down: decreases voltage, primary coil has more turns than secondary
The transformer equation:
Input voltage / output voltage = pri coil turns / sec coil turns
Equation to calculate power output
power in = power out
pri voltage x pri current = sec voltage x sec current
