Magnetic Fields U4

Question 0

What is the right hand rule

Answer 0

Thumb = current

Curled fingers = Magnetic field direction

Question 1

What does each finger mean for Flemings left hang rule

Answer 1

Thumb = force
First finger = magnetic field
Second finger = current

Question 2

Define magnetic field strength

Answer 2

It is a measure of the magnetic field per unit area

Question 3

What is B measured in

Answer 3

Tesla

Question 4

Is B scalar or vector? Why?

Answer 4

Vector because it has magnitude and direction

Question 5

Magnetic flux =

Answer 5

BA

Question 6

What are the two equations for flux linkage

Answer 6

N x flux

NBA

Question 7

What’re the units of flux linkage and flux

Answer 7

Weber (Wb)

Question 8

What happens to a wire carrying a current in a magnetic field

Answer 8

It will experience a force

Question 9

When does a force act on a wire in a magnetic field

Answer 9

If the wire is carrying current and the wire cuts the magnetic field lines

Question 10

When is the force zero (acting on a current carrying wire in a magnetic field)

Answer 10

If the current is parallel to the flux lines

Question 11

What is always the direction of the force always perpendicular to

Answer 11

Current

Magnetic field

Question 12

F = ? when a current carrying wire at right angles to a magnetic field is proportional to the current

Answer 12

BIL

Question 13

Define the B from BIL

Answer 13

The force on one metre of wire carrying a current of one amp at right angles to the magnetic field

Question 14

When is force greatest acting on a current carrying wire

What is this in terms of an equation?

Answer 14

When the wire and field are perpendicular

Bsin(theta)

Question 15

For a wire at angle theta to the field the force acting on the wire is given by

Answer 15

F = BILsin(theta)

Question 16

What are the stages of a motor

Answer 16

1) the coil has an electric current round the core and provides a field that interacts with two oppositely poles permanent magnets
2) the fields repel each other causing a resultant force and anticlockwise motion (due to the LHR)
3) as the cool turns half way, perpendicular to current, it gets close to vertical then disconnects from the commutator
4) momentum carries the coil over the vertical point then the commutator reconnects
5) due to there being current flowing again in the cool the resultant force is restored so it spins

Question 17

When the coil gets to halfway it is perpendicular to what

Answer 17

Current

Question 18

Why is emf induced in a motor situation

Answer 18

There is a change in flux in the coil

Question 19

What increasing the emf do to speed

Answer 19

It increases it

Question 20

Why does the speed increase when the emf increases

Answer 20

Because there’s an increased rate of change in flux

Question 21

When the magnetic field increases what decreases

Answer 21

Current

Question 22

When a charged particle has velocity what does it act perpendicular to
What does this cause

Answer 22

Field therefore it has circular motion