Induced Potential And Transformers Flashcards
What is the generator effect?
A potential difference is induced across the ends of the conductor if the conductor is moving relative to a magnetic field or the magnetic field around the conductor changes
In a complete circuit there will be an induced current
It can be seen by a wire moving in a magnetic field cutting field lines
Moving a magnet in and out a coil of wire
What factors affect induced current?
The direction of induced pd and current reverses if the movement of the wire or magnet is reversed or the polarity of the magnet is reversed
If this happens repeatedly an ac current is produced
Induced pd increases if the speed of movement, strength of magnetic field or number of turns increases
An induced current will generate a magnetic field around the conductor that opposes the original change producing it. This acts to slow down changes in magnetic field
How does a transformer work?
Changes the size of the alternating potential difference
Two coils wound around an iron core
An ac current passes through the primary coil producing an alternating magnetic field in the iron core. The alternating magnetic field in the iron core induces the alternating pd in the secondary coil
Vp/ Vs = Np/ Ns
What happens if a transformer is 100% efficient?
Power output = power input
Vs x Is = Vp x Vs
What happens in a step up transformer?
There are more turns on the secondary coil than on the primary coil so a greater p.d through the secondary coil
Current in the secondary coil must be less than the current in the primary coil
How do alternators work?
When the coil is made to turn in a magnetic field, a current is induced in the coil
The ends of the coil are connected to a slip ring, keeping a continuous connection with the coil and lets the current flow out the coil, through the brushes and into a circuit
The current changes direction every half turn
The induced p.d is maximum when the plane of the coil lies parallel to the magnetic field lines
Induced p.d is 0 when the plane of the coil is perpendicular to the magnetic field lines
How do dynamos work?
The split ring commutator makes the ends of the coil swap contacts with the circuit very half turn so the current always flows in the same direction relative to the magnetic field. The induced p.d Inma dynamo varies from 0 to a maximum value twice each cycle nut never goes in the opposite direction
How do microphones work?
Generator effect
Converts variations in pressure in a sound wave into variations in electrical current
The coil is attached to a diaphragm
The coil is placed inside a permanent magnet
When a sound wave hits the diaphragm, it vibrates, making the coil vibrate inside the magnetic field of the magnet
This induces a current in the coil
The alternating p.d induced in the coil has the same frequency as the sound waves which make the diaphragm vibrate
