Electromagnetism Flashcards
What is a magnetic field?
A region where magnetic materials feel a force
2 things a magnetic field can be created by
- Magnets
- Current flowing in a wire
3 ways to increase the size of the force on the wire
- Increase the current
- Increase the magnetic field strength
- Increase the number of wires in the field
What is the Motor Effect?
Force produced on a wire is used to create movement (rotational)
How can you predict the direction of the force produced on a wire?
Fleming’s Left Hand Rule
What is Electromagnetic Induction?
Electricity is induced (created) when a wire cuts through magnetic field lines
In generators, the output voltage/current is proportional to
1) the speed of rotation
2) the number of turns on the coil
The output voltage/current in a generator can be increased if…
The magnetic field strength increases
How can the direction of the induced current in a generator be predicted?
Fleming’s Right Hand Rule
How is electricity created in the second coil? (QWC)
- The alternating current in the primary coil creates a changing magnetic field around it
- Iron is a magnetic material and so easily transmits this magnetic field to the secondary coil
- The constantly changing magnetic field around the secondary coil induces a voltage in this coil
What is magnetism?
Physical phenomenon produced by motion of electric charge which results in attractive and repulsive forces between objects
What will happen when the north pole of a magnet and a south pole of a magnet are pushed towards each other?
They will attract
What will happen when 2 north poles of a magnet or 2 south poles of a magnet are pushed towards each other?
They will repel
Field line rules
- Show shape of magnetic field
- Direction of field lines (North to South)
- Strength of magnetic field (Closer together = stronger)
Magnetic materials
-Steel/Iron
-Cobalt
-Nickel
(Remember SINC)
How can magnetism be induced in magnetic materials?
- Placing in magnetic field
- Stroking them with another magnet
What is the difference between magnetically soft and magnetically hard materials?
Soft:
-Gain and lose electrons easily
Hard:
-Harder to magnetise but retain their magnetism
What is an electromagnet?
Magnet that can be turned on and off by flow of electricity
What is a solenoid?
Electromagnetic with many coils
What can a solenoid be used for?
Can be used as electromagnets, inductors in electric circuits and as miniature wireless receiving antennas
What happens when 2 magnetic fields interact?
They attract or repel
What happens when a current carrying wire passes through a magnetic field provided by 2 bar magnets?
Direction of induced current reversed if wire is moved in opposite direction or field reversed
How can you increase force experienced by metal conductor (wire)?
- Increase speed of movement
- Increase magnet strength
What is the role of a commentator in a motor?
Ensure current always flows in same direction
Uses for Motor Effect
Motor Effect rotates an object e.g. propeller, simple electronic motor, rotating CDs
3 things magnetic field lines show on a bar magnet
- The shape of the field
- The direction (out of North pole, into South)
- The strength of the field (lines closer together = stronger field)
What does a split ring commutator do?
Ensures force on left of motor is always upwards and force on right is always downwards so that the coil turns continuously in one direction
What device makes use that electricity can be created (induced) by a changing magnetic field?
Transformer
What do transformers do?
Increase (step-up) or decrease (step-down) voltage
