Magnetism and electromagnetism Flashcards

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1
Q

What is a permanent magnet?

A

A magnet that produces it’s own magnetic field

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2
Q

What is an induced magnet?

A

Magnetic materials that turn into a magnet when they’re put into a magnetic field

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3
Q

How does a compass work?

A

Inside is a bar magnet; the north pole is attracted to the south pole of any magnet near which means that it points in the direction of any magnetic field, including the earth’s own one, which is why a compass always points north

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4
Q

What happens when a current flows through a wire?

A

A magnetic field is produced around the wire, made up of concentric circles perpendicular to the wire

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5
Q

How can the strength of a magnetic field be effected?

A

The larger the current is or the closer to the wire you are, the stronger the magnetic field

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6
Q

What is a solenoid?

A

A coil of wire

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7
Q

How can a solenoid be used for a magnetic field?

A

By wrapping the wire into a solenoid, the strength of the magnetic field is increased as the field lines around each loop of wire line up with each other, meaning that there are lots of field lines pointing in one direction

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8
Q

How can you increase the field strength of a solenoid?

A

By putting a block of iron in the centre as it turns into an induced magnet (this is called an electromagnet) or by adding more coils to it

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9
Q

Why are electromagnets useful?

A

They only work when a current is flowing through the solenoid, meaning they can be turned on and off, which a permanent magnet can’t

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10
Q

What are the main uses of electromagnets?

A

In scrap yards to pick up then release certain metals and within other circuits to act as switches

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11
Q

What is the motor effect?

A

When a current carrying wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and the conductor to exert a force on each other

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12
Q

How can the wire experience the full force during the motor effect?

A

The wire has be at 90 degrees to the magnetic field as the force always acts at right angles to the magnetic field and the direction of the current in the wire

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13
Q

How does the force acting on the wire become increased?

A

If the strength of the magnetic field is increased or if the current running through the wire is increased

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14
Q

How do you find the size of the force acting on a wire?

A

Magnetic flux density x current x length

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15
Q

Which fingers represent what in Fleming’s left hand rule?

A

The thumb is force, the first finger is field and the second finger is current

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16
Q

How can the direction of the motor by reversed in a magnetic field?

A

By reversing the current or by swapping the magnets

17
Q

How does a loudspeaker work?

A

An ac is sent through a coil of wire which surrounds one magnetic pole and is surrounded by the other and is attached to the base of a paper cone, the force acts in the opposite direction when the current reverses, variations in the current cause the cone to vibrate, causing the air particles to vibrate and variations in pressure create a sound wave

18
Q

What is the generator effect?

A

The induction of a potential difference (and current if there’s a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field

19
Q

How do you create current in the generator effect?

A

By moving a magnet in a coil of wire from side to side, a small amount of current will be created but only whilst the magnet is still moving

20
Q

How is alternating current produced in the generator effect?

A

Moving the magnet or conductor in the opposite direction will reverse the potential difference/current, so if you keep the magnet moving backwards and forwards, a potential difference is produced which keeps swapping direction

21
Q

What happens when a change in the magnetic field induces a current in the wire?

A

When a current flows ANOTHER magnetic filed is induced around the wire

22
Q

What does a magnetic field created by an induced current do?

A

It always acts against the change that made it

23
Q

How do you change the size of an induced pd?

A

You have to change the rate that the magnetic field is changing

24
Q

How do you increase induced pd?

A

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

25
Q

How do alternators generate alternating current?

A

They work just like generator, except instead of a split ring commutator, they have slip rings and brushes so that the contacts don’t swap every half turn to keep it the same direction; this means they produce an alternating potential difference

26
Q

How does a dynamo generate direct current?

A

It works in the same way as alternators except has a split-ring commutator instead of slip rings which swaps the connection every half turn to keep the current flowing int the same direction

27
Q

How does a microphone work?

A

Sound waves hit a flexible diaphragm that is attached to a coil of wire wrapped around a magnet, causing the coil of wire to move in the magnetic field, generating a current. This sis basically the opposite of a loudspeaker