Magnetic fields

Question 1

What happens when current passes through wire?

Answer 1

Magnetic field is induced forming concentric rings

Question 2

What is magnetic flux density and its unit?

Answer 2

measure of the strength of field, T (tesla)

Question 3

How to have a maximum force exerted on wire?

Answer 3

Current must be perpendicular to the field

Question 4

What is the equation of a charged particle following a circular path?

Answer 4

BQV = mv2 / r

Question 5

What is supplied to cause the charged particles to move in cyclotron?

Answer 5

high frequency alternating voltage

Question 6

Why charged particle travel in a semi-circular path in dee

Answer 6

The charged particle experiences a force due to the magnetic field which is perpendicular to the direction of travel.

Force acts as centripetal force for a circular motion

Question 7

What happens when the particles reach the edge?

Answer 7

They are accelerated by electric field which causes them to move across. When it reaches again, the alternating electric field changes direction so accelerated again (etc.)

Question 8

What is magnetic flux (phi)

Answer 8

the magnetic field passing through a given area

Question 9

equation of magnetic flux linkage

Answer 9

N(phi) = BAN

Question 10

How is emf induced in rod? (electromagnetic induction)

Answer 10

When rod moves relative to a magnetic field, the electrons experience a force. Thus builds up on one side.

Question 11

What is Faraday’s law

Answer 11

The magnitude of induced emf is equal to the rate of change of flux linkage

Question 12

What is Lenz’s Law?

Answer 12

induced emf acts in such a direction to produce effects that oppose the change causing it.

Question 13

1. In Lenz’s law experiment, what happens as the magnet approach the coil?

Answer 13

there is a change of flux through the coil so an emf and current is induced

Question 14

2. In Lenz’s law experiment, due to Lenz’s law, what happens to the magnet?

Answer 14

pole will be induced in order to repel the magnet thus slowing it down due to electrostatic force of attraction

Question 15

3. In Lenz’s law experiment, what happens to magnet as it passes through coil?

Answer 15

no change in flux, so no emf is induced

Question 16

4. In Lenz’s law experiment, what happens to magnet as it leaves?

Answer 16

there is a change of flux so a current is induced that opposes the motion of magnet which then attracts the magnet moves up

Question 17

Where is the peak voltage?

Answer 17

distance from equilibrium to max point

Question 18

root mean square voltage?

Answer 18

average of all squares of the possible voltages

Question 18

root mean square voltage?

Answer 18

average of all squares of the possible voltages

Question 19

In step-up transformer, which one has more turns

Answer 19

secondary has more than primary

Question 20

What is the main cause of energy loss in transformer?

Answer 20

eddy currents which are induced by alternating magnetic field in primary coil and form a loop

Question 21

How are eddy current formed?

Answer 21

Eddy current oppose the field that produced the,. reducing field’s flux density and causes energy to be lost

Question 22

Effects to reduce eddy currents (laminated iron core) -made out of, causes

Answer 22

laminated iron core - core is made up of layers of iron between insulator. This is because eddy current cannot pass through insulator so amplitude decreases.

Question 23

another effect to reduce eddy currents

Answer 23

high resistivity metal

Question 24

How to reduce energy loss in resistance in coil?

Answer 24

thick wire

Question 25

How to reduce energy loss if core not easily magnetised?

Answer 25

soft iron core allow easy magnetisation and demagnetisation

Question 26

How to reduce energy loss if core not easily magnetised?

Answer 26

soft iron core allow easy magnetisation and demagnetisation