Magnetism

Question 1

What is the Lorentz Force?

Answer 1

Magnetic forces always act perpendicular to the direction of the motion of the charged particles.

Question 2

What is the Lorentz Force Law?

Answer 2

𝐅 = 𝑞 (𝐯 × 𝐁)

Question 3

What is the Hall effect?

Answer 3

• The Hall effect is the production of a potential difference (the Hall voltage) across an electrical conductor
• that is transverse to an electric current in the conductor
• and to an applied magnetic field
• perpendicular to the current.

Question 4

Give the parameters for the equation:

I = NevA

Answer 4

I = Current
N = Number of electrons per unit volume
e = Electronic charge
v = Drift velocity
A = Cross-sectional area of the bar

Question 5

For Fleming’s left hand rule, state what each finger represents.

Answer 5

ThuMb = Motion / Force
First = Magnetic Field
SeCond = Current

Question 6

What is the right hand curl rule for finding the direction of vector S for a current loop?

Answer 6

Thumb = S
Fingers = I

Question 7

Explain why ε0 is known as permittivity of free space.

Answer 7

In vacuum, there are no molecules to be polarized, so 𝜀0 is called permittivity of vacuum of free space.

Question 8

What is the magnetic dipole moment?

Answer 8

m = I x S

Where:
m = magnetic dipole moment
I = current
S = direction of wire

Question 9

What are the units for the magnetic dipole moment?

Answer 9

A m^2

Question 10

How could you find the direction of the magnetic dipole moment?

Answer 10

Fleming’s right hand rule.

Question 11

What is the right hand curl rule for finding the direction of the magnetic field caused by a current in a wire?

Answer 11

Thumb = I
Fingers = B

Question 12

What is µ0?

Answer 12

µ0 is the vacuum permeability

Question 13

What is the value of µ0?

Answer 13

µ0 = 4π x 10^-7

Question 14

What are paramagnetic materials?

Answer 14

Paramagnetic substances have a weak magnetism resulting from the presence of atoms (or ions) that have permanent magnetic moments.

Question 15

What happens to the magnetic field of a solenoid if a paramagnetic material is placed inside?

Answer 15

Its atomic moments line up with the field.

The magnetic field has a small increase.

Question 16

What are diamagnetic materials?

Answer 16

Diamagnetic materials have no magnetism.

E.g. water, wood, etc

Question 17

What happens to the magnetic field of a solenoid if a diamagnetic material is placed inside?

Answer 17

A weak magnetic moment is induced in the direction opposite to the magnetic field of the solenoid.

The magnetic field has a small decrease.

Question 18

What are ferromagnetic materials?

Answer 18

Ferromagnetic substances contain permanent atomic magnetic moments.

Question 19

What happens to the magnetic field of a solenoid if a ferromagnetic material is placed inside?

Answer 19

The permanent magnetic moments align parallel to each other in the direction of the solenoid’s magnetic field.

The magnetic field has a large increase.

Question 20

Explain how the magnitude of a magnetic field are represented by magnetic field lines.

Answer 20

The number of magnetic field lines per unit area (density of field lines) represents the magnitude.

Question 21

Explain how the direction of a magnetic field are represented by magnetic field lines.

Answer 21

The arrows on the field lines show the direction of the magnetic field.

Question 22

What is Farday’s Law of Induction?

Answer 22

ε = - dΦ(B) / dt

Where:
ε = induced voltage
dΦ(B) = change in magnetic flux
dt = change in time

Question 23

What is the magnetic flux through a solenoid?

Answer 23

Φ = (total number of turns) x (area of solenoid turn) x (magnetic field)

Φ = (NL) (πr^2) (B)

Where L is the self inductance

Question 24

What is the magnetic flux through a surface?

Answer 24

Φ(B) = ∫ B * dA

Question 25

What is the equation for a magnetic field due to a current-carrying wire at a distance r away?

Answer 25

B = µ0 I / 2πr

Question 26

What is the equation for angular frequency?

Answer 26

ω = 2π / T = v / r

Question 27

What is the equation for centripetal force?

Answer 27

F = mv^2 / r

Question 28

What is the equation to find the force per unit length between two wires?

Answer 28

F / ΔL = (µ0 I(1) I(2)) / (2πr^2)