Magnetic Fields

Question 1

Where do arrows in magnetic fields point?

Answer 1

North to South

Question 2

What is the right-hand rule for solenoids?

Answer 2

Fingers curl in direction of the current, thumb points towards north pole of that solenoid.

Question 3

What is the right-hand rule for a current-carrying wire?

Answer 3

Thumb points in direction of current, fingers will then curl in direction of field.

Question 4

What is magnetic field strength known as?

Answer 4

Magnetic flux density, symbol B.

Question 5

What is flux density defined as?

Answer 5

The force per unit length per unit current on a current-carrying conductor at right angles to the direction of the mag field.

Question 6

What is the unit for flux density?

Answer 6

Tesla, T

Question 7

What is 1 Tesla equal to?

Answer 7

The flux density that causes a force on 1N on 1m of wire carrying 1A.

Question 8

What is magnetic flux?

Answer 8

The number of flux lines passing through an area at right angles to the field the flux passes through. Wb = BA. Basically un-densitying flux density.

Question 9

What is the formula for magnetic flux linkage?

Answer 9

N Flux = BAN

Question 10

What is the unit of magnetic flux linkage?

Answer 10

Weber-turns, Wb-turn.

Question 11

What diagram explains flux linkage?

Answer 11

A coil of N turns with flux flowing straight through the middle of it.

Question 12

What happens if the magnetic field is at an angle theta to the normal of the face of the coil in flux linkage?

Answer 12

Then N flux = BAN cos theta

Question 13

What is flux linkage through a single coil of wire?

Answer 13

flux = BA cos theta

Question 14

What do the symbols represent in the flux linkage equation?

Answer 14

B is magnetic flux density, A is area of wire, N is number of turns of the wire.

Question 15

What is the fore on a current-carrying wire in a mag field?

Answer 15

F = BIL when perpendicular to the field lines.

Question 16

What is Fleming’s left-hand rule?

Answer 16

Thumb points in direction of force, 1st finger from north to south in mag field, second finger points in direction of current.

Question 17

What is the force on a moving charge in a mag field?

Answer 17

F = BQv, v is velocity and Q is charge. At right angles to a magnetic field. If not at a perfect right angle is BQv sin theta.

Question 18

How do you find the radius of the path of a charged particle in a mag field?

Answer 18

Use mv^2 / r = BQv, so r = mv/BQ

Question 19

What is the movement of a charged particle in a magnetic field?

Answer 19

Force on this is always at right angles to velocity, so acts as a centripetal force and so it will move in a circular path with a constant speed.

Question 20

How do cyclotrons work?

Answer 20

1. Charged particles (protons) fired into middle of cyclotron
2. Mag. field forces charged particles to follow a circular path out of first field
3. P.D between 2 fields accelerates particle across gap
4. Particle is moving faster so has a larger radius through 2nd field.
5. P.D reverses so particle then accelerates again.
6. Particle does this a lot, gets very fast then leaves cyclotron.

Question 21

What are the uses of cyclotrons?

Answer 21

Producing high energy beams of particles, useful for radiation threapy.

Question 22

What are equations relating to cyclotrons?

Answer 22

r = mv/BQ so time for semi-circle is mpi/BQ = r
so speed upon leaving is v = BQR/m
Period of alternating P.D is 2m pi / BQ
Frequency of alternating P.D therefore = BQ / 2 pi m