5.5 Magnetic Fields

Question 1

Define

Magnetic Field

Answer 1

A magnetic field is a region in space where any material with magnetic properties will experience a force.

Question 2

Equation

Force on a Current-carrying Conductor in a Magnetic Field

Answer 2

F = BiL

Question 3

Define

Magnetic Flux Density

Answer 3

The force per meter experienced by a conductor carrying a current of 1A when it is perpendicular to the magnetic field.

Question 4

Define

Magnetic Flux

Answer 4

The product of surface area and component of magnetic flux density normal to the area.

Question 5

Equation

Magnetic Flux

Answer 5

Φ = BA

Φ = BAcosθ

Question 6

Equation

Magnetic Flux Linkage

Answer 6

NΦ = NBA

Question 7

State

Faraday’s Law of Electromagnetic Inducation

Answer 7

The magnitude of the induced EMF is directly proportional to the rate of change of the magnetic flux linkage.

Question 8

State

Lenz’s Law of Electromagnetic Induction

Answer 8

The direction of the induced EMF tends to oppose the magnetic flux change causing it, and does oppose it if a current flows.

Question 9

uEquation

Induced EMF

Answer 9

Average EMF = ^(∆NΦ)⁄_∆t = ^(∆NBA)⁄_∆t

Question 10

Equation

Induced EMF in a Conductor Moving Through a Uniform Magnetic Field

Answer 10

E = BLv

Question 11

Equation

Induced EMF in a Rotating Coil

Answer 11

E = BANωsin(ωt)

E_max = BANω

Question 12

Explain

How does a Transformer work?

Answer 12

• An alternating voltage is applied across the primary coil, casuing an alternating current to flow in it.
• This produces a periodically changing magnetic field in the primary coil and the softy iron core carries this magnetic field through the secondary coil.
• The secondary coil now has a changing flux linkage causing an alternating EMF to be indaced in it, casuing an alteranting current to flow in it. This induced EMF has a frequency equal to that of the alternating voltage supplied to the primary coil.

Question 13

Explain

Types of Transformers

Answer 13

Step up
* Used to increase voltage
* Number of turns in secondary coil (N_s) > Number of turns in priamry coil (N_p)
* Voltage in secondary coil (V_s) > Voltage in primary coil (V_p)
Step down
* Used to decrease voltage
* Number of turns in primary coil (N_p) > Number of turns in secondary coil (N_s)
* Voltage in primary coil (V_p) > Voltage in secondary coil (V_s)