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Flashcards in Electromagnetism Deck (47):

How would you plot magnetic field lines using a plotting compass?

You'd move the compass gradually around the edges of the bar magnet and makes marks in the places where the arrow of the compass points, then plot all the points together


Give four examples of magnetic materials.



What rule is used to know which way the magnetic field travels around a current carrying wire?

Right hand thumb rule


Which way does a magnetic field travel in a bar magnet?

North to south


What is a permanent magnet?

A magnet that produces its own magnetic field


What is an induced magnet?

A magnetic material that becomes a magnet when put into a magnetic field


What two things make the magnetic field around a current carrying wire stronger?

A shorter distance from the wire
A higher current carried


What is an electromagnet?

A magnet whose magnetic field can be switched on or off using an electric current


What is a solenoid?

A coil of wire


Why does having more coils in an electromagnet make it stronger?

The field lines around each loop line up with each other so there will be lots of them, all close together


Give one example of a use of an electromagnet.

Switches in circuits


What is the motor effect?

The act of movement being created by a current carrying wire being placed in between two magnets


True or false?

For the motor effect, the wire should be at 90 degrees to a magnetic field to experience full force



What will happen in the motor effect if the wire runs parallel to the magnetic field?

There will be no force/movement at all


What is magnetic flux density?

The amount of field lines that there are in a region
i.e. The strength of the magnet


How do you find the direction of the force which has the motor effect?

Fleming's left hand rule


How does Fleming's left hand rule work?

1. Point your first finger in the direction of the field
2. Point your second finger in the direction of the current
3. Your thumb will then point in the direction of the force


How do electric motors use the motor effect?

The current carrying wire between the two magnets cause a force to be exerted, and (use Fleming's left hand rule) one will be up and one will be down meaning the movement created is a rotation


How does a motor continue to spin using the motor effect rather than swap back and forth?

It has a split ring commutator to swap the direction of the current every half turn and therefore swap the direction of the forces.


Define the term generator effect.

The induction of a potential difference (and current if there's a complete circuit) in a wire which is experiencing a change in magnetic field


True or false?

The force between a permanent magnet and an induced magnet is always attractive



Give some ways on how you might increase the strength of a solenoid.

More coils
Increase the tightness of the coils
Add an iron core
Increase the current


True or false?

In the motor effect, the strength of the force increases with the strength of the magnetic field and the amount of current passing through the conductor.



True or false?

The force between a permanent magnet and an induced magnet is always attractive.



What is the magnetic field like inside a solenoid?

Strong and uniform
It has the same strength and direction at every point in that region


True or false?

In the motor effect, the magnitude (strength) of the force decreases with both the strength of the magnetic field and the amount of current passing through the conductor.

It increases


What kinds of 'change in magnetic field' would be experienced in the generator effect?

A magnet is moved into a coil of wire
The wire is moved
A magnet is rotated
The wire is rotated


Why is a potential difference induced in the generator effect?

Because the wire experiences a force which transfers energy


How can a potential difference induce an alternating current?

A continuous movement backwards and forwards of the magnet or coil cause the potential difference to keep changing direction so induces the alternating current


True or false?

In the generator effect, an induced current always opposes the change that made it.



Give two ways to increase the size of an induced potential difference?

Increase the speed of the movement
Increase the strength of the magnetic field


What is the difference between an alternator and a dynamo?

Alternators generate alternating current
Dynamos generate direct current


What would use an oscilloscope for relating to the generator effect?

To see the generated potential difference


What would an oscilloscope trace for an alternating potential difference?

A sinusoidal curve


Would an oscilloscope trace for a direct potential difference?

Repetitive 'hills' (curved lines)
Never crosses 0


Do loudspeakers use the generator effect or the motor effect?

Motor effect


Describe how a loudspeaker works.

- An alternating current is sent through a coil of wire attached to the base of a paper cone
- The coil surrounds one pole of a permanent magnet while it's surrounded by the other pole meaning the current causes a force on the coil (so the cone moves)
- When the current alternates, the movement occurs in the opposite direction because the force does too
- This causes the cone to vibrate and therefore the air to vibrate and create variations in pressure which create a soundwave


How could you alter a sound wave produced by a loudspeaker?

Change the frequency of the alternating current as this will also change the frequency of the sound wave


Do microphones use the generator effect or the motor effect?

Generator effect


Describe how a microphone works.

- Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet
- The sound wave causes the coil of wire to move into the magnetic field and so generates a current


True or false?

In microphones, the movement of the coil depends on the properties of the sound wave.



Do transformers use the generator effect or the motor effect?

Generator effect


True or false?

Transformers only work with a direct current.

They only work with an alternating current


What do transformers do?

Change the size of the potential difference of an alternating current


What happens in a transformer if an alternating current is applied across the primary coil?

The iron core magnetises and demagnetises quickly and the changing magnetic field therefore induces an alternating potential difference in the secondary coil
If the secondary coil is part of a complete circuit, a current is induced too


What's the difference between step-up transformers and step-down transformers?

Step-up transformers increase the potential difference - they have more turns on the secondary coil
Step-down transformers decrease the potential difference - they have more turns on the primary coil


Why is energy carried at a high potential difference through the national grid?

So the current is low, which reduces energy wasted to surroundings