Chapter P15- Electromagnetism Flashcards
What are bar magnets?
What two things do bar magnets have?
What do like poles do to each other?
What do opposite (or unlike) poles do to each other?
What two metals can be magnetised and what does this mean?
What can any metal be if it contains iron in it?
What two other metals can only be magnetised?
What are the only three magnetic metal?
What is magnetic induction?
Why does this always happen?
What do magnetic fields always go from?
What is pure iron?
What two things can happen to pure iron?
What is steel?
What two things can happen to steel?
Permanent magnets
A north and a south pole
Repel each other
Attract to each other
Iron and steel meaning turned into magnets
Magnetised
Cobalt and nickel
Iron, cobalt and nickel
When an magnetised metal bar is magnetised by holding a permanent magnet near it
So that the metal will be attracted to the permanent magnet
North to South
A soft magnetic material
It is easy to magnetise but loses its magnetism easily
A hard magnetic material
It is harder to magnetise but keeps its magnetism.
What is steel used to make?
What is a solenoid?
What are three ways to make an electromagnet stronger?
What is an electromagnet?
What does an electromagnet consist of?
What is an example of an electromagnet?
Magnets
A coil of wire
- Increase the current
- To use a magnetic material as the core
- Increase the turns of the coil of wire
A solenoid that has an iron core
An insulated wire wrapped around an iron bar
A coil.
What does a circuit breaker act as?
What is this held closed by?
What happens when the current reaches a level that is too large?
How does this occur for?
What happens in an electric bell when current flows through the circuit enabling what?
What does this then do?
What does the armature then do?
What is the relay used to switch?
What cause the armature to be attracted to the electromagnetic in a relay?
What does this then do enabling what?
A switch in a series circuit
A spring
The electromagnet becomes strong enough that it pulls the switch open
The switch stays open until it’s reset manually
The armature is attracted towards the electromagnet, hitting the bell
Breaks the circuit so the current stops
Springs back into place which connects the circuit starting the process again
An electric machine on or off
A small current flowing through the coil around the iron core
This closes the switch gap completing the other circuit with a much higher current.
What happens a current passes through a wire in a magnetic field?
What is this called?
In what two ways can the size of the force be increased?
When is the force on the wire at its strongest?
When would the force be equal to zero?
What three parts are all at right angles to each other?
What is the magnetic flux density of a magnetic field?
What is this measured in?
What three factors affect the size of the force on a wire?
It can experience a force
The motor effect
- Increasing the current
- Using a stronger magnet
When the wire is perpendicular to the magnetic field
When the wire is parallel to the magnetic field
The direction of the current, the magnetic field and the force
A measure of the strength of the magnetic field
Tesla (T)
The current; the size; the magnetic flux density.
What is the equation that’s used to calculate magnetic flux density?
What can be created using the motor effect?
What’s this called?
Force= Magnetic flux density x Current x Length
A motor that spin when we put a current through it
An electric motor.
What does the secondary potential diference produce depend on?
What is this transformer equation?
What are transformers almost?
What would happen if a transformer was 100% efficient?
What would be the equation showing this?
What would be the other equation for showing this remembering that P= V x I?
The ratio of the number of turns of the primary coil compared with the number of turns of the secondary coil
pd of primary coil (Vp) -:- pd of secondary coil (Vs) =
no of turns of primary coil (Np) -:- no of turns of secondary coil (Ns)
Almost 100% efficient
It would transform all of the power in the primary coil to the secondary coil
Pp= Ps
Vp x Ip= Vs x Is.
In what two ways can we increase the force on a coil?
What are the different stations in creating electricity?
What two factors are transformers used to change and from where does this occur?
What is a step up transformer used to increase?
What does this means concerning current?
What is connected to the ac supply?
What is the secondary coil part of?
What happens when an AC current is supplied to the primary coil?
What then happens and then leading to what?
Why do transformers only work with alternating current?
- Increasing the current
- Increasing the number of coils
Furnace—Turbine—Generator—Step Up—Transformer
—The National Grid
The voltage (and current) of the electricity as it’s transferred from the power station to our homes
A step up transformer is used to increase the voltage of the electricity travelling in the cables on transmission lines
The current is lower so less energy is lost as heat to the surroundings
The primary coil
The circuit you need a different voltage for
It produces an alternating magnetic field
That magnetic field passes through the secondary coil and induces an alternating voltage in it
Because they need a changing magnetic field to induce the current in the second wire.
What is a step up transformer used to increase?
What do they have more turns of?
What is a step down transformer used to decrease?
What do they have fewer of and where?
What does Fleming’s Left-Hand Rule tell you?
In what two ways is the direction of the force reversed?
What can you see using Fleming’s Left-Hand Rule?
What is the motor effect?
The voltage
More turns on the secondary coil than they have on the primary coil
Used to decrease the voltage
Fewer turns on the secondary coil than they have on the primary coil
How the directions are related to each other
If either the direction of the current or the magnetic field is reversed
The force on each side of the coil will act in different directions
When a current flows through a wire which is in a magnetic field, the wire experiences a force.
Describe the generator effect in detail?
What would happens if it’s a complete circuit?
What does this induced current then generate?
What is an alternator?
What happens when the coil is turned?
What does an alternator generate and what does this do?
When is the size of the induced potential difference the greatest?
When is this induced potential difference equal to zero?
What is the frequency of the induced alternating current the same as?
What will a stronger magnet do?
When a wire (without a current flowing through it) is moved through a magnetic field, a potential difference is induced across a wire
This will induce a current
A magnetic field that opposes the original
An alternating-current generator
A current flows
Generates a current that is repeatedly changing direction
When the coil is parallel to the direction of the magnetic field lines
When perpendicular to the field lines
The frequency at which the coil turns
Increase the peak potential difference too.
What is dynamo?
What does this machine use, and like what else?
What does this mean happens at each half rotation of the coil?
What is the definition of sound waves?
What happens in a microphone?
What is a diaphragm?
What does this then generate and what is this interpreted as?
A direct current generator
A split ring commutator (exactly like a motor)
The current changes direction through the wire but the connections to the rest of the circuit mean a direct current is received
Pressure changes in the air
Sound waves make a small diaphragm vibrate, moving a coil which is inside a magnetic field
A thin sheet of metal
Generates potential difference which is interpreted as an electrical signal.
Describe what happens in a loudspeaker in detail?
What is the coil attached to and what does this cause?
An alternating current is put through a coil in a magnetic field which forces the coil to move due to the motor effect
The coil is attached to the diaphragm which causes pressure changes in the air.
