Magnetic Field

Question 1

In terms of north and south, which way do Fields lines act away from and act towards

Answer 1

Act away from north poles and towards south poles

Question 2

Define a Tesla

Answer 2

The magnetic flux density that produces a force of newton per metre on a current of one ampere flowing in a direction perpendicular to the magnetic field

Question 3

Define magnetic flux density and give equation related

Answer 3

Magnetic flux density at a point is equal to the force per unit length on a conductor carrying a unit current in a direction perpendicular to the field
F= B x I x L

Question 4

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Question 6

In a magnetic field, why is the work done on a moving charge equal to zero and explain why the charge moves at a constant speed in a magnetic field

Answer 6

Question 7

Discuss process that occurs when a proton is inserted between plates of a cyclotron

Answer 7

Process continues until it reaches the edge where it leaves a cyclotron
In the next Dee, it travels in a bigger semi-circle as velocity has increased (r=mv/BQ)

Question 8

Why are dees in a cyclotron connected to an AC current

Answer 8

To create an electric field

Question 9

What is SI unit of flux

Answer 9

Question 10

Draw graph of electric field strengh against seperation (radius)

Answer 10

Question 11

How to keep electron moving straight in between parallel plates

Answer 11

Fe = EQ, Not Fb

Question 12

Derive an equation for time in a circular in a semi-circular path

Answer 12

Pi x r / v comes from distance / speed

Question 13

What happens when a magnet is pushed into a coil

Answer 13

Question 14

Define induced emf

Answer 14

The electrical work done on a unit charge flowing once around the circuit

Question 15

What is faraday’s law

Answer 15

The magnitude of emf is proportional to rate of change of flux linkage

Question 16

What is Lenz’s law

Answer 16

The direction of an emf tends to produce a current which opposes the change causing it

Question 17

Why must Lenz’s law exist

Answer 17

Question 18

Draw two graphs of flux linkage against time and emf against time as you move a magnet in and out of a coil

Answer 18

As the actual equation for magnitude of induced emf is e = - Flux linkage / change in time
Note that is not taking the negative into account in formula sheet

Question 19

Answer 19

Missing info from end :
This means potential difference is reversed and current flows the other way

Question 20

How to calculate emf induced here

Answer 20

Question 21

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Question 22

Draw a graph to represent this

Answer 22

Question 23

What are the graphs of flux linkage against time and emf against time

Answer 23

Flux = cos graph
emf = negative sin graph

Question 24

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Question 25

State what is meant by Vrms and Irms

Answer 25

Vrms - value of DC voltage that would that would provide the same average power per cycle as the AC supply Irms - is same but just swap word voltage for current

Question 26

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Question 27

Provide solutions for these heat loss methods in transformers

Answer 27

Question 28

How is heat lost to Eddy currents in transformers

Answer 28

Question 29

How is heat lost to hysterical losses in transformers

Answer 29

Question 30

How is heat lost to flux losses in transformers

Answer 30

Question 31

What would happen if transformer was used with a direct current

Answer 31

Question 32

An oscilloscope has a screen of eight vertical and ten horizontal divisions. Describe how you would use oscilloscope to provide alternating waveform in the graph so two cycles are available

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Question 35

Answer 35

Vertical line formed Trace just moves up and down

Question 36

Unit for flux linkage

Answer 36

Wb - webner

Question 37

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Question 40

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C

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Answer 47

A

Question 48

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A

Question 50

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D

Question 51

Answer 51

A

Question 52

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Question 53

Answer 53

Current travels in opposite direction too charge

Question 54

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Question 55

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Question 58

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Question 59

Explain why the ions travel in a semicircular path whilst in the magnetic field.

Answer 59

magnetic field is perpendicular to velocity force is perpendicular to both magnetic field and velocity (or Fleming's left hand rule) (hence) force acts perpendicular to velocity force changes direction of velocity but not its magnitude force remains perpendicular to velocity as direction changes

Question 60

Outline the essential features of a step-down transformer when in operation.

Answer 60

primary coil with more turns than secondary coil Input is AC (alternating current)

Question 61

The transformer circuit includes a fuse. Explain why this is necessary

Answer 61

fuse prevents transformer from overheating [or prevents transformer from supplying excessive currents

Question 62

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Question 63

Explain why the ions have no overall deflection when a magnetic field of the required strength has been applied

Answer 63

magnetic force = electric force or BQv = EQ these forces act in opposite directions, are balanced and resultant vertical force is zero

Question 64

Explain how a step-down transformer differs in construction from a step-up transformer

Answer 64

primary coils must have more turns than secondary coils

Question 65

Derive emf = BLv

Answer 65

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