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Eleanor Rowe Physics > Magnetism > Flashcards

Magnetism Flashcards

1
Q

What direction does magnetic field go

A

North to south

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2
Q

What is a magnetic field

A

Region where other magnets experience a force

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3
Q

What do compares do

A

Show magnetic field as are attracted to South Pole of magnet
Normally face north as earth has own field

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4
Q

What are permenant magnets

A

Magnets that produce own magnetic field

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5
Q

What are induced magnets

A

Magnetic material that become magnetic when in field eg iron or steel
When take away magnetic field quickly lose magnetism and stop making own field

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6
Q

What does the right hand thumb rule show

A

Moving current creates magnetic field

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7
Q

How does strength of field produced by a current change

A

With increases current or distance from wire

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8
Q

What is a solenoid

A

A coil of wire that produces a magnetic field
Increases strength of field produced by straight wire
Field lines look like bar magnet

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9
Q

How can the field strength of a solenoid be increased

A

Add iron core in coil

Iron becomes induced magnet when current flows

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10
Q

What is an electromagnet

A

A solenoid with iron core connected to a current, where the current can be turned on or off meaning that the magnetism of the magnet can be controlled

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11
Q

What are the two main uses of electromagnets

A

To move scrap metal, to pick up is turned on, to drop is turned off
Act as switches in circuits, when switch is closed electromagnet attracts iron contact which completed circuit, turning on motor

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12
Q

When does the motor effect occur

A

When a current carrying wire or conductor of current is put between magnetic poles,
the field around wire interacts with the magnetic field placed in, causes wire and conductor to exert force on each other, making one of them move

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13
Q

What condition does there have to be for the motor effect to occur

A

The wire or conductor must be at 90 degrees to the magnetic field

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14
Q

How can you increase strength of force felt in motor effect

A

Increase strength of magnetic field or increase current

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15
Q

What is magnetic flux density and what is it measured in

A

It is the amount of field lines in a region

Measures in Tesla’s (T)

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16
Q

What does each finger in Flemings left hand rule represent

A

Thumb is motion
First finger is field
Middle finger is current

17
Q

How do electric motors work

A

Forces act on two side arms of a coil of wire carrying a current
Coil is on spindle and forces act one up one down causing it to rotate
Split ring commutator swaps contact every 1/2 turn to keep same rotating direction

18
Q

How do loudspeakers work

A

AC through coil of wire attached to base of paper cone
Coil surrounds 1 pole of magnet and is surrounded by the their pole
Interaction of fields causes force on coil, so cone moves
Movement of cone causes sound waves as air vibrates

19
Q

What does the generator effect do

A

Creates PD in a conductor, and also a current is conductor is part of complete circuit

20
Q

How does the generator effect occur

A

Moving a magnet in a coil of core or moving conductor in a magnetic field
Shifting magnet from side to side creates blip in current
If move magnet in opposite direction Pd/current is reversed
So I’d keep moving magnet back and forth, AC current flows

21
Q

How can you change the size of an induced PD through the generator effect

A

Increase speed of movement as cuts through more field lines

Increase strength of magnetic field so more lines to cut through

22
Q

How do alternators create AC

A

Generators rotate coil in magnetic field (constructed like a motor)
As coil spins, current is induced in coil and it changes direction every 1/2 turn
Instead of split ring commutator, it has slip rings and brushes so contacts don’t swap, so AC is produced

23
Q

How do dynamos create DC

A

Have split ring commutator instead of slip rings, so connection is swapped every half turn, so current flows same direction and direct current is produced

24
Q

What is an oscilloscope

A

Graph that shows how generated PD is charged

25
Q

What does the oscillograph look like for AC current

A

Normal wave line diagram

26
Q

What does oscilloscope look like for DC

A

Bouncing on top half of axis

27
Q

How do microphones work

A

As loudspeakers in reverse
Sound waves hit flexible diaphragm attached to coil, wrapped around magnet
Causes coil to move in field, generating current
Movement of coil depends on properties of sound wave
Current links to speaker, gives off sound

28
Q

What happens when AC goes across primary coil of transformer

A

The iron core magnetises and demagnetises quickly

The changing field induced Pd and or current in 2nd coil

Eleanor Rowe Physics (11 decks)

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