Magnetic Fields

Question 1

Define a magnetic field

Answer 1

A region in space where a force acts on a moving charged particle/ current carrying conductor/ a magnetic material.

Question 2

Define magnetic flux. Provide formula.

Answer 2

Phi =BAcos(theta)
It is the product of the magnetic flux density and the area. The area is perpendicular to the direction of the magnetic field.

Question 3

Define magnetic flux density

Answer 3

F = BIL

The force per unit current per unit length on a conductor placed at 90º to a magnetic field.

Question 4

State the equation of the magnetic force experienced by a current carrying conductor.

Answer 4

F = BILsin0

0=angle between wire and magnetic field. Want the component perpendicular to magnetic field.

Question 5

State the equation of the magnetic force experienced by a moving charge

Answer 5

F = Bqvsin0

Question 6

Define the tesla.

Answer 6

Uniform magnetic flux normal to long straight wire carrying a current of 1A creates force per unit length of 1Nm^-1.

Question 7

Explain what type of force will two parallel wires experience depending on the direction of their currents.

Answer 7

-If both current go in the same direction then they will experience an attractive force.
-If the current are in opposite directions they will experience a repulsive force.

Question 8

Equation for velocity selector. (relates v and the magnetic and electric fields.)

Answer 8

v = E/B

Question 9

In the formula for hall voltage: Vh = BI/ntq. What does n and t represent.

Answer 9

n= number density of charge carriers
t = thickness of the side that is parallel to the magnetic field.

Question 10

Why is a hall probe made of silicon rather than copper?

Answer 10

This is because silicon has a smaller number of n so it will give a greater hall voltage.

Question 11

When measuring with a hall probe how do you get a maximum reading? And minimum?

Answer 11

-The reading is 0 when the plane of the hall probe is parallel to the direction of the magnetic field lines.
-The reading is at its maximum when the plane of the hall probe is perpendicular to the direction of the magnetic field lines.

Question 12

State faraday’s law

Answer 12

The size of the induce e.mf. is directly porportinal to the rate of change in flux linkage.

Question 13

State Lenz’s law

Answer 13

The induced e.m.f is in the direction such that it opposes the change in flux that caused it.

Question 14

How can a magnetic field be produced?

Answer 14

-Magnetic fields are produced by current-carrying conductors, moving charges or by permanent magnets.

Question 15

How can you Increase Magnetic field due to a current in solenoid.

Answer 15

USing a ferrous(iron) core

Question 16

What is the motion of a charged particle when at right angles to a magnetic field.

Answer 16

In this case the magnetic force will always be perpendicular to its velocity, hence the magnetic force will act as a centripetal force.

Question 17

Explain how electric and magnetic fields can be used in velocity selection

Answer 17

It is used to select particles of specific velocity. We can place electric and magnetic fields perpendicular to each other. PArticles whose velocity equals the ratio E/B would come out undeflected.

Question 18

Define the hall effect

Answer 18

The production of voltage across a conductor when a current flows through the conductor at right angles to a magnetic field.

Question 19

How does a hall probe work?

Answer 19

-A small current flows through the probe across the ends; when a magnetic field is applied, electrons are pushed sideways by the magnetic force.
-Electrons are accumulated on one side of the probe leaving the other side with a lack of electrons.
…this creates an electric field between the two sides.
-The charge is detected by a small voltage across the probe.
-The greater the magnetic flux density the greater the hall voltage.

Question 20

Define magnetic flux linkage

Answer 20

It is defined as the prodcuct of the magnetic flux and the number of turns

Question 21

Define the Weber

Answer 21

One weber is the flux that passes through an area of 1m^2 when the magnetic flux density is 1T.