Magnetic Fields

Question 1

Define magnetic field and what is it characterised by?

Answer 1

A magnetic field is a region in which a current-carrying conductor, a moving charged particle or a magnetic material experiences a force.

+It is characterised by a magnetic flux density and a direction.

Question 2

Define magnetic field line

Answer 2

A magnetic field line is the path along which an isolated magnetic North pole would accelerate when released in a magnetic field.

Question 3

Magnetic field density B in
1. Straight wire
2. Flat circular coil
3. Solenoid

Answer 3

1. Straight wire
   B ∝ I/r
   B = (μ.I) / 2πr
2. Flat circular coil
   B = (μ.ΝI) / 2r
3. Solenoid
   B = μ.nI
   n - no of loops per unit length.
   B is halved at the ends of the solenoid

Question 4

How to increase flux density for a solenoid

Answer 4

1. Increase current
2. Insert a soft magnetic material w/in the solenoid which increases μ
3. Increase number of loops per unit length of solenoid by winding a second layer of coils above the first.

Question 5

Define the motor effect

Answer 5

The motor effect is the phenomenon whereby an electromagnetic force is exerted or a conductor carrying current (non-parallel direction) to a magnetic field.

F = (BIL)ㅗ

Question 6

Electromagnetic force + Centripetal force

Answer 6

F = BIL sinθ
= Β(q/t)(vt)sinθ
= Bqvsinθ

Electromagnetic force = centripetal force
Bqv = (mv²)/r
r = (mv) / (Bq)

Question 7

Magnetic field density B

Answer 7

Measured in tesla T

B is the force per unit length of conductor per unit current flowing normally to the field

Question 8

Magnetic flux

Answer 8

Magnetic flux Φ is the number of field lines passing through an enclosed area.

Φ = BㅗA
= BAcosθ
Unit: Weber; Wb
1 T = 1 Wb m^-2

Question 9

Magnetic flux linkage special type of Φ in C.B. officially represented by λ

Answer 9

λ = Φ×Ν
= BAN
SI unit: Weber; Wb.