Electromagnetism (Chapter P5/P15) Flashcards
What is a magnetic field
A region around a magnet where magnetic materials experience attractive magnetic forces
How do you make a stronger electromagnet
More turns of wire on the coil
Add an iron core
Use a larger current
What is a solenoid
A long coil of insulated wire which produces a strong magnetic field
What is a use of a electromagnet
Electric bell
what is a relay
A switch operated by an electromagnet
What is the motor effect
It is when a force is exerted on a wire when between magnets and carrying a current
How can we predict the motor effect
The left hand rule
How does an electric motor work
The force between the 2 magnetic fields from the magnets and the wire cause the coil to turn.
The commutator allows the coil to fully spin in 1 direction
How do you reverse the spin of a motor
Change the direction of the current
Switch the magnets around
How does a loud speaker work
A coil of wire wrapped around a tube is placed over the north pole magnet.
The alternating current means that the direction of the coil is changing.
This causes the coil to create sound waves
what is the equation for force involving magnetic flux density
Force = Magnetic Flux Density x Current x Length of Wire F = B x I x L
What is electromagnetic induction
It is the creation of current by moving magnets near a circuit
How can you increase the current induced by electromagnetic induction
Changing the speed of the magnet
Using a stronger magnet
Use more coils
What is an alternator
It is a machine which uses the motor effect to create a alternating potential difference
How does an alternator work
The coil rotates between two magnets and every half cycle the slip rings change charge and the current flows the opposite direction in the circuit
What is a dynamo
It is a machine that uses the generator effect to create a direct current
How does a dynamo work
The coil rotates between two magnets and instead of slip rings there is a commutator.
The commutator keeps the two connections the same charge and so creates a direct current
What are the similarities between a dynamo and an alternator
Both use the generator effect
Both use a conductor passing through a magnetic field
Both create a current from a potential difference
What are the differences between a dynamo and an alternator
The dynamo generator uses split rings instead of slip rings
The dynamo generator creates a direct current instead of an alternating current
A alternator’s arm of coil reverses every 180 degrees of rotation whereas the dynamos generator’s split rings lose contact every 180 degrees of rotation
what is a transformer
It is a machine which changes the current across a wire
How does a transformer work
An a.c. current in the primary coil creates a changing magnetic field in the iron core
This magnetic filed goes through the secondary coil and induces a potential difference across it
This creates a current through the secondary coil
What is the equation involving number of turns and voltage
Np = Vp
Ns Vs
What is the equation for power
Power = Voltage x Current
What material makes up the core of a transformer
Magnetically soft iron
What is the National Grid
It is the system of distributing electricity from power stations to homes
What does a step up transformer do
It increases the voltage across a wire
What does a step down transformer do
It decreases the voltage across a wire
What voltage is the grid and super grid
132,000 Volts and 400,000 Volts
what is the equation for power loss
P = Current squared x resistance
What are the 3 pins called in a plug
earth - green and yellow
Live - Brown
Neutral - Blue
What is the earth wire
It is a connection between the earth and the metal case of the appliance
If the live wire touches the case the electricity flows through the wire to the earth as it has a low resistance
What does the square inside a square symbol represent
Double insulated
what happens when the current flows through the earth wire
The fuse melts from the really high current
What do double insulated appliances not have
An earth wire as there is no metal in the appliance
