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Magnetism and Electromagnetism II - Coggle Diagram
Magnetism and Electromagnetism II
Generator effect
Basics
The generator effect is the induction of a potential difference in a wire which is moving relative to the magnetic field, or experiencing a change in magnetic field
If there is a complete circuit, a current will flow in the wire
If you move the magnet in the opposite direction, then the pd will be reversed, if the polarity of the magnet is reversed, the pd/ current will be aswell
If you keep the magnet moving backwards and forwards, you produce a pd that keeps swapping direction, like ac
If an electric conductor is moved throuhg a magnetic field, it cuts through magnetic field lines and a potential difference is induced across the ends of the wire
A moving magnet in a coil of wire causes a changing magnetic field which induces a potential difference between the ends of the wire
An induced charge generates a magnetic field that opposes the original change
Generators
You can create ac/ dc by turning a magent end to end in a coil
As you turn the magent, the magnetic field through the coil changes, the change in magnetic field produces a pd, making a current flow through a wire
When you've turned the magnet throuhg half a turn, the direction of the magnetic field through the coil reverses, so current flows in the opposite direction
If you turn the magent in the same direction, the pd will keep on reversing every half turn, and you'll get alternating current
Converts kinetic energy into electrical
Alternators
Alternators rotate a coil in a magnetic field
As the coil spins, cutting magnetic field lines, a pd is induced across the coil, if the circuit is complete, the current is also induced
Instad of a split ring commutator, ac generators have slip rings and brushes so the contacts don't swap every half turn
Every half turn, the potential difference reverses direction, and every hald turn the current changes direction, but since the connections are never broken, the current alternates
Dynamos
They have a spilt ring communtators, instead of slip rings
This swaps the connection every hald turn, to keep the curent in the same direction
Microphones
Loudpseakers in reverse
Sound waves hit a flexible diaphragm that is attachd to a coil of wire, wrapped around a magnet
This causes the coil of wire to move in the magnetic field, which generates an alternating pd and thus a current
The movement of the coil depends on the properties of the sound wave, louder sounds make the diaphragm move more
Microphones convert pressure variations of a sound wave into variations in current in an electric circuit
Sound to electrical
Increasing current
Increase the speed of movement, more magnetic field lines are cut
Increase the strenght of the magnetic field
Increasing the number of coils on coils on the solenoid
The motor effect
Basics
When a current carrying wire is put between magnetic poles, the magentic field around the wire interacts with the magentic field it has been placed in
The magent and the conductor exert a force on eachother, this can cause the wire to move
To experience the full force, the wire has to be at 90 degrees to the magnetic field, if it is parallel, it won't experience any force at all
The force always acts at right angles to the the magentic field of the magents and the direction of the current
The magnitude of the force increases with the strength of the magnetic field
Force also increases with the amount of current passin through the conductor
Finding the size of the foce
Force acting on a conductor in a magnetic field depends on three things
Magentic flux density - how many field lines there are in a region, shows the strength of the magnetic field
Size of the current through the conductor
Length of the conductor in the magnetic field
Flemings left hand rule
First finger - direction of the field
Second finger - direction of the current
Thumb - Direction of the force
If either the current or magnetic field is reverse, then the direciton of the force will also be reversed
A motor
There are two forces acting on the opposite sides of the coil in opposite directions, these equal and opposite forces cause the coil to rotate
Because on one side of the armature the current is going away from us and on the other it is coming towards us, there are two forces acting, one up and one down
The split ring communtator swaps the contacts every half turn, which reverses the current and as a result the force, meaning that the motor rotates in the sam direction
The direction of the motor can be swapped by reversing the polarity or the dc supply
Use Flemings left hand rule to work out which direction the coil will turn
Loudpseakers
An alternating current is set through a coil of wire attatched to the base of a paper cone
The coil surrounds one pole of a magnet, and is surrounded by the other pole, so the current causes a force on the coil
When the current reverses, the force acts in the opposite direction, causing te cone to move in the opposite direction too
Variations in the curren make the cone vibrate, making the air around the cone vibrate causing variations in pressure and creating a sound wave
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 wave produced
Electrical to kinetic
Changing rotation speed
Increase the size of the current
Increasing the magnetic flux density
Increasing the number of turns
Chaning direction
Reversing direction of the current
Reverse direction of the magnetic flux between the magents