P7 - Electromagnetic effects (to be continued) Flashcards

1
Q

An electromotive force (e.m.f) is needed for a

A

current to flow

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2
Q

What are the two ways to increase the magnitude of an induced e.m.f

A
  1. increase the field strength

2. Increase the speed at which the wire is moved

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3
Q

What is the motor effect

A

when a wire carrying an electric current passes through a magnetic field perpendicularly and experiences a force for both the field and wire

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4
Q

What does the size of the force depend on in the motor effect

A

The magnitude of the current and strength of the field

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5
Q

What is the use of Fleming’s left hand rule

A

it predicts the direction of the force

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6
Q

What does the thumb represent in Fleming’s left hand rule

A

force

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7
Q

what does the index finger in Fleming’s left hand rule

A

field

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8
Q

what does the third finger in Fleming’s left hand rule

A

current

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9
Q

An electric motor transfers electrical energy to

A

kinetic energy

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10
Q

What is an electric motor made from

A

a coil of wire positioned between the poles of two permanent magnets

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11
Q

In an electric motor what happens

A

The current passing through the wire creates a magnetic field which interacts with the magnetic field produced by the two magnets exerting a force on the sides of the coil

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12
Q

What is the job of a split ring commutator in a d.c motor

A

ensure that a motor continues to spin by reversing the direction of the current so the forces on the coil are reversed and continue rotating

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13
Q

In a d.c motor what does the motor coil experience

A

one side feels a force upwards and the other side feels a force downward creating a spin

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14
Q

Without a commutator what would happen to the motor

A

It would rotate 90 degrees and then just stop making it useless

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15
Q

3 ways to make the motor spin faster

A

Increase the current
Increase the strength of the magnetic field
Increase number of turns of wire in the coil

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16
Q

If you change the direction of current or reverse magnetic field what direction does the motor spin in

A

the opposite direction

17
Q

An e.m.f is induced in a wire in a complete circuit when

A

The wire is moved through a magnetic field
or
Magnetic field is moved past the wire
or
Magnetic field around the wire changes strength

18
Q

A direct current (d.c) is produced when

A

a steady current is produced by a battery that passes from the negative to positive terminal of the battery

19
Q

In a (d.c)

A

voltage stays constant throughout the circuit

20
Q

What is current where the electrons in a circuit move back and forth

A

alternating current (a.c)

21
Q

Electricity generated at power stations is

22
Q

What is a dynamo

A

a simple current generator

23
Q

Turning the permanent magnet inside a coil

A

reverses its magnetic field every time the magnet is rotated 180 degrees

24
Q

The dynamo induces a

A

alternating current in the wires of the coil.

25
Power stations use rotating electromagnets instead of
permanent magnets to create a magnetic field
26
The frequency in a dynamo depends on
how fast it's spinning
27
What does a transformer consist of
two coils of insulated wire on a piece of iron
28
When alternating voltage is applied to the first (primary) coil it produces a
changing magnetic field in the core which induces an alternating e.m.f in the secondary coil
29
Why is the strength of a magnetic field increased in the transformer
because the iron is soft and easily magnetized
30
What happens when there are more turns on the secondary coil than the primary coil
the voltage across the secondary coil will be greater than the voltage across the primary coil
31
What is the term for when a secondary coil has more turns than the primary coil
step up transformer
32
A transformer with fewer turns on the secondary coil than the primary coil is called
a step down transformer
33
The voltage and turns are _________ in a transformer
proportional
34
If the primary coil has 100 turns and input is 12V and the secondary coil has 500 turns how many V is the output
6V
35
If the primary coil has 1000 turns and input is 12V and the secondary coil has 4000 turns how many volts does it produce
48V
36
Formula for turns and voltage in transformer
primary coil voltage/secondary coil voltage = number of primary turns/number of secondary turns