| 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 |
| Drawing of a magnetic field around a straight current-carrying wire | Diagram |
| 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. |
| Diagram of the Right Hand Thumb Rule | Diagram |
| 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 |
| What does the magnetic field of a solenoid look like | Diagram |
| What direction does the magnetic field in a solenoid go towards | From N to S like a normal Magnet |
| 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. |
| Diagram of a Simple dc electric motor | Diagram |
| 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 |
| Components of a Loudspeaker | Diagram |
| 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 |
| Image of generator effect | Diagram |
| 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 you enlarge the entire wave of the trace cycle in the oscilloscope of the generator effect | by increasing the strength of the magnetic field |
| What does a direct PD trace cycle look like | Image |
| 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 |
| Diagram of microphone | Diagram |
| 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 |
| Diagram of the basic structure of a transformer | Diagram |
| 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. |
