Magnetism and Electromagnetism Flashcards
Define:
Magnetic Field
A region where other magnets or magnetic materials experience a force
Define:
Permanent Magnets
Produce their own magnetic field
Define:
Induced Magnets
Magnetic materials that turn into a magnet when put into a magnetic field
Descrribe:
Right-Hand Thumb Rule
Using your right hand, point your thumb straight in the direction of the current and curl your fingers.
The Thumb represents the direction of the current
The curled fingers represent the direction of the Magnetic Field
Describe:
Solenoid
Wire wrapped into a coil to produce a stronger magnetic field
Define:
Electromagnet
A solenoid with an iron core
Describe:
Uses of Electromagnets
Lifting objects - e.g. cranes
Used as switches in other circuits
Define:
The Motor Effect
When a current-carrying wire interacts with a magnetic field causing it and the magnet to exert a force on each other. This can cause the wire to move
Equation:
Force on a Conductor in a Field
F = BIL
Force = Magnetic Flux Density x Current x Length
Describe:
Fleming’s Left-Hand Rule
Using your left hand, point your index finger in the direction of the magnetic field, point your middle finger perpendicular to the index finger in the direction of the Current, and point your Thumb straight. The Thumb will be in the direction of the Force
Describe:
Electric Motors
1) Forcs act on the two side arms of a coil of wire that are carrying a current
2) These forces are just the usual forces which act on any current in a magnetic field
3) Because the coil is on a spindle and the forces act one up and one down, it rotates
4) The split-ring commutator is a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction
5) The direction of the motor can be reversed either by swapping the polarity of the dc supply or by swapping the magnetic poles over
6) You can use Fleming’s left-hand rule to work out which way the coil will turn
Describe:
Loudspeakers
1) An alternating current is sent through a coil of wire attached to the base of a paper cone
2) The coil surrounds one pole of a permanent magnet, and is surrounded by the other pole, so the current causes a force on the coil
3) When the current reverses, the force acts in the opposite direction, which causes the cone to move in the opposite direction too
4) So variations in the cureent make the cone vibrate, which makes the air around the cone vibrate and creates the variations in pressure that cause a sound wave
5) The frequency of the sound wave is the same as the frequency of the ac, so by controlling the frequency of the ac you can alter the sound wave produced
Define:
The Generator Effect
The induction of a potential difference (and current if there’s a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field.
Describe:
Alternator
Rotates a coil in a magnetic field using an alternatic current with slip rings and bushes
Describe:
Dynamo
Rotates a coil in a magnetic field using a direct current using a split-ring commutator
Describe:
Microphones
1) Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet
2) This causes the coil of wire to move in the magnetic field, which generates a current
3) The movement of the coil (and so the generated current) depends on the properties of the sound wave (louder sounds make the diaphragm mover further)
4) This is how microphones can convert the pressure variations of a sound wave into variations in current in an electric circuit
Describe:
Step-up Transformer
Increase potential difference
Decrease current
More turns on secondary coil than primary coil
Describe:
Step-down Transformer
Decrease potential difference
Increase current
More turns on primary coil than secondary coil
Equation:
Transformers
Input p.d / Output p.d = Turns primary coil / Turns secondary coil
P.d secondary x Current secondary = P.d primary x Current primary
