electromagnetism Flashcards

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1
Q

State in what direction do field lines around a magnet go:

A

north to south

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2
Q

List some magnetic materials:

A

-steel
-iron
-cobalt
-nickel

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3
Q

What is the term when an object is made into a magnet

A

induced magnetism

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4
Q

What is the difference between induced magnets and permanent magnets

A

permanent magnets produce their own magnetic field, where as induced magnets are placed into a magnetic field and can lose its force when removed.

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5
Q

What are magnets?

A

magnets are objects that can make a non-contact force that repels or attracts.

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6
Q

Describe how a current can cause a magnetic field:

A

A conductor with a current can develop a magnetic field only when the current is flowing. Making the current flow the other way will reverse the direction of the magnetic field.

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7
Q

What symbols show that the field lines are coming out / in of a page in a diagram

A

out = circle with a dot in the middle
in = circle with a cross

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8
Q

What is the motor effect?

A

the interaction between an external magnetic field and the magnetic field of an induce wire causing a physical force to be exerted on the wire.

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9
Q

Write the equation relates magnetic flux density, force, current and length.

A

force (N) = magnetic flux density (T) x current (A) x length (m)

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10
Q

Define magnetic flux density:

A

the strength of a magnetic field.

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11
Q

What is Fleming’s left hand rule?

A

The rule which relates the direction of the current (middle), external field lines (pointer) and force (thumb) on a wire in a motor effect sample.

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12
Q

What is Fleming’s right hand rule??

A
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13
Q

What is the human hearing range?

A

20Hz- 20kHz

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14
Q

Describe what sound waves are:

A

sound waves are longitudinal waves that have areas of compression and rarefaction

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15
Q

Explain how a loudspeaker works:

A
  1. an amplifier supplies an AC into a wire coil, making it generate its own magnetic field.
  2. the coil is coiled around the permanent magnet, where the two magnetic fields interact and cause a motor effect.
  3. the AC causes the coil to move out and in as the magnetic fields continuously repel and attract each other (the alternating current changes the direction).
  4. the coil is attached to a flexible cone, and the motor effect causes a resultant force to move the the coil with the cone.
  5. the repetitive movement cause sound waves to be generated
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16
Q

What would you change in a loudspeaker to adjust the pitch and volume?

A

-to increase the pitch, you increase the AC
-to increase the volume, increase the voltage.

17
Q

What is the generator effect?

A

When a wire passes though a magnetic field, a potential difference is induced at the ends of the wire. Changing the direction of the wire passing will change the direction of the potential difference and when there is no movement there is no voltage generated. If you put a loop of a wire through a magnetic field the potential difference created will create a current in the wire

18
Q

How can you increase the impact of the motor effect?

A

-increase the current in the wire
-make the wire longer (coil it)
-increase the magnetic flux density of the external magnets
-make the two fields as perpendicular as possible

19
Q

How would you reverse the motor effect’s direction?

A

-reverse the direction the current in the wire
-flip the external magnetic field’s direction.

20
Q

How can you increase the impact of the generator effect?

A

-increase the magnetic flux density of external magnets.
-move the wire faster
-increase the mount of wire that passes through the magnetic field (coil it)

21
Q

How would you reverse the generator effect’s induced current’s direction?

A

-change the direction of movement
-switch the poles external magnet

22
Q

Explain how a current can be created when an ammeter circuit passes through a U-shaped magnet:

A
  1. the north and South Pole of the magnet create its ow magnetic field, whose lines go from north to south
  2. as the wire circuit passes through the magnetic field ad cuts it in one direction, a potential difference is created.
  3. the potential difference pushes a current through the wire in one direction.
    4.this is detected and measured by the ammeter.
  4. when the wire cuts the field lines in the opposite direction, the p.d reverses, generating an opposite current.
23
Q

in an electric motor, what does the split ring commutator do?

A

it reverses the current’s direction every half turn so that the motor effect doesn’t get counteracted when it fully turns, allowing the coil to move in one continuous motion rather than rocking back and forth to a rest vertically.

24
Q

In a generator, describe and explain the relation between the potential difference and position of a rotating coil suspended in a magnet’s magnetic field.

A

when the coil is parallel to the field lines, it generates the maximum potential difference because the wire is passing the field lines at its maximum velocity as much as possible.

when the coil is perpendicular to the field lines, the potential difference drops to 0 because its furthest away from the strongest point of the magnetic field and isn’t cutting them at all.

25
Q

Describe the wire in an alternator:

A

a wire with both ends connected to two different commutators which allow the induced current to flow out of the coil.

26
Q

Describe the wire in dynamo:

A

a wire with both ends connected to a split ring commutator which allows the potential difference to not shift directions, providing a direct current.

27
Q

Give ways on which we may increase the potential difference / frequency induced by an alternator.

A

P.D -
- make the magnetic field stronger
-increase the number of coils

Frequency-
-make relative motion quicker.

28
Q

Describe a graph showing the potential difference induced as a coil rotates in an alternator:

A

when perpendicular to the field lines, the p.d is at 0, when it starts to parallel, the p.d increases to its peak, as it completes half a rotation back to a vertical position, the p.d decreases to 0, when it continues to rotate to a parallel position the p.d increases to its peak, but is in the negatives as the p.d switches directions.

this creates a graph where one full rotation looks like sideways s starting at the origin.

29
Q

Describe a graph showing the potential difference induced as a coil rotates in a dynamo:

A

when perpendicular to the field lines, the p.d is at 0, when it starts to parallel, the p.d increases to its peak, as it completes half a rotation back to a vertical position, the split ring maintains the direction of the current as it switches the wire ends even when the p.d changes direction. this means as it completes the second half of the turn, the potential difference peaks again in the positive side of the graph before going back to 0 as it becomes perpendicular.

this creates an m shaped graph starting at the origin.

30
Q

What is a transformer and include examples:

A

an electrical device that changes the potential difference supplied by a supply to a different potential difference for an appliance. e.g a mobile charger, an adapter, a step up/down transformer.

31
Q

What are the main components of a basic transformer:

A

at least two coils (different amounts of coils) wound round a laminated iron core.

32
Q

What is the formula that relates the number of turns and the voltage in a transformer?

A

Number of coils (primary) / Number of coils (secondary) = Voltage of wire (primary) / Voltage of wire (secondary)

33
Q

How does a transformer work

A