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GCSE PHYSICS: ELECTROMAGNETISM


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[Front]


How does the magnetic field outside of the coil of a solenoid act
[Back]


Like a normal bar magnet (round from North to South)

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How does the magnetic field outside of the coil of a solenoid act
Like a normal bar magnet (round from North to South)
How does the magnetic field outside of the coil of a solenoid act
Like a normal bar magnet (round from North to South)
What does a current carrying wire have
It contains as a magnetic field as its an electromagnet
What is the Right Hand Thumb Rule
Using your right hand, point your thumb in the direction of the current, and curl your fingers. The direction of your fingers is the direction of the field.
Factors affecting the strength of the magnetic field
If current increases, magnetic field strength increases (Current directly proportional) The closer you are to the wire, the stronger the magnetic field strength (Distance inversly proportional)
What is a solenoid
Wrapping a wire into a coil to increase the strength of the magnetic field
How to increase the magnetic strength of a solenoid
Wrap the coil around a piece of iron (Iron becomes induced and combined magnetic field is stronger) Adding more turns to the solenoid (field lines closer so stronger) Increase current flowing through the coil
How does the magnetic field inside of the coil of a solenoid act
Acts uniform (same direction adn strength at every direction)
How does the magnetic field outside of the coil of a solenoid act
Like a normal bar magnet (round from North to South)
Uses of electromagnets
Since you can turn on and off a electromagnet It is useful for switches (Electric Bell) For magnets on cranes at scrapyards
How to determin where N and S is in a solenoid
If the coil is anticlockwise, it is North pole If the coil is clockwise, it is South pole
What is the Motor effect
When a current carying wire (electromagnet) is placed in a magnetic field of two magnets (N to S), the wire experiences a force
What is the Left hand Flemming Rule
F (Force) [Thumb] B (magnetic flux density) [Index] I (Current) [Middle]
Calculating the size of the force
F = BIL F = force (Newtons) [N] B = magnetic flux density (Tesla) [T] I = Current (Amps) [A]
Components of a Simple dc electric motor
A Motor with a loop of wire inbetween the two magnets A DC current The force acts downwards and the wire turns vertical and gets stuck as it cannot rotate anymore. The split ring commutator reverses the direction of the current and makes the rotation continue A split ring commutator is just a conducting ring with a gap between the two halves. As it rotates, the part of the commutator that is touching each contact chagnes every half turn.
How to increase speed of simple dc electric motor
By increasing the Current By increasing the strength of the magnetic field Using a coil instead of a single loop of wire
How to change direction of a simple electric motor
Swapping the polarity of the direct current supply Swapping the magnetic poles
Explanation of a loudspeaker
The AC current in the loudspeaker means the wire moves clockwise then anticlockwise tonnes of times, causing vibrations in the air pressure causing sound waves to be formed Controlling AC frequency will generate different sound waves.
What is a Generator effect
The generator effect is the induction of a potential difference (and current if there's a complete circuit) across a conductor which is experiencing a change in an external magnetic field
The potential difference can be induced through 2 ways
Moving the electrical conductor in a magnetic field Or Moving or changing a magnetic field relative to the electrical conductor
When is a current produced in the generator effect
When it is a complete circuit that is being used in the generator
Creating a generator effect with a coil and a permanent magnet
The permanent magnet rotates in the coil or The permanent magnet moves forwards and backwards in and out
What happens to the electromagnet/wire when the wire stops moving or changes direction of movement (up and down, left and right)
Potential difference dissapears when stopped moving The direction of the potential difference (negative and positive) swaps each time we swap direction
How to change the size of the induced potential difference
Changing the strength of the magnetic field (stronger magnets), so theres a larger potential difference move the wire, or magnets more quickly so the magnetic field will change more, so its a bigger potential difference Shape the wire into a coil so there are more turns so the field lines are closer so tehre is a bigger potential difference
Difference between generator and motor effect
Motor effect has current already, generator effect generates pd and current from 0
What is an alternator
An alternator genrates alternating current and every half turn done, the pd and current changes direction but the slip rings and brushes on the alternator makes it so the contacts dont swap every half term. This will mean they collect AC rather than DC
What is a Dynamo
An dynamo generates DC using a split ring commutator that does swap the contact point every half turn.
Why doesnt a generator's wire move without human input
As it has no current to do motor effect. The structure of the circuit and magnets are the same, but current isnt there for generator and is there for motor. A motor uses current to exert force A generator uses force to generate current
What is an oscilloscope
A device used to see the generated potential difference.
What is the x and y axis on a oscilloscope
X axis = Time Y axis = Voltage
How do you increase the peak of the trace cycle in the oscilloscope of the generator effect
Increasing the frequency of rotations in the generator. This would also squash the trace cycle horizontally.
How do microphones work
Microphones generate current from sound waves Sound waves hit a flexible diaphragm that is attached to a coil of wire wrapped around a magnet. The sound waves causes the coil of wire to move back and forth in the magnetic field which generates a current. The movement of the coil depends on the proeprties of the sound wave that hits the flexible diaphragm This is how microphones can convert the different sound waves into variations in current in a circuit
What is the basic structure of a transformer
Consists of two coils, the primary and the secondary, wrapped around an iron core. Iron is used for the corea because it can magnetise and demagnetise quickly
How does a transformer work
When an AC flows through the primary coil in a transformer it produced a magnetic field which magnetises the iron core Due to the AC, the magnetic field in the iron core alternates. This constantly changing field cuts through the secondary coil The changing field induces an alternating potential difference across the ends of teh secondary coil by the generator effect If the secondary coil is part of a complete sicruit, this pd causes an ac to flow, it has the same frequency as the atlernating current in the primary coil
What does the size of the pd at the secondary coil depend on
Size of the pd across the primary coil Number of turns on each coil
Remember this about transformers
It doesnt carry charge from the first coil to the second. The magnetic field does this
Why wont you get any significant pd or current at the secondary coil if there is DC put into primary coil
There wont be a constant changing force to cut the secondary coil's magnetic field and make a pd
What are step up and step-down transformers
They change an electrical supply so that the size of the output pd is not the same as the input pd
Ratio between the primary and secondary pd compared to the ratio of number of turns on the priamry coil and secondary coil
The ratio of First coil PD: Second coil PD is the same as Number of turns in First Coil: Number of turns in the Second Coil
A step up transformer
THe number of turns on the secondary coil and the size of the pd across it are greater than across the primary coil
A step down transformer
The number of turns on the secondary coil and the size of the pd across it are bigger than across the primary coil
Where are step up and step down transformers used in
The national grid Step up increase pd of the supply for transmission around the country via power lines This means the current is lower meaning less energy is lost in heating.