Magnetic Field

Question 1

What’s the units for magnetic flux density (B)

Answer 1

Tesla (T)

Question 2

What’s the units for flux linkage (ø)

Answer 2

Whebber Turns (Wb-turns)

Question 3

Magnetic line go from — to —

Answer 3

North to south

Question 4

What do each finger stand for in Flemings left hand rule

Answer 4

First = Field
SeCond = Current
Thumb = Force

Question 5

What is EMF equal to when induced by a magnetic field

Answer 5

Rate of change of flux linkage

Question 6

Define magnetic flux

Answer 6

The magnetic field passing through a given area. Given by the product of the magnetic flux density and the area.

Question 7

Explain how a shaker torch with a diode can light the LED inside.

Answer 7

• As the magnet moves through the coil there’s a charge in magnetic flux linkage
• An EMF is induced across the coil
• This generates a current in the circuit
  -Diode only allows D.C
• Capacitor is charged repeatedly
• When switch closes current charges the LED

Question 8

How does a step-up transformer work.

Answer 8

• a.c in primary produces a changing magnetic flux/field
• The magnetic flux is linked the the secondary coil by the iron core
• The changing magnetic flux induced an EMF in the secondary coil
• More turns on the secondary will increase the rate of change of flux linkage according to faradays law

Question 9

A superconducting sphere is dropped through two coils with magnetic fields in the same vertical direction. Explain why this leads to a current within the sphere? (2)

Answer 9

The ball cuts the magnetic flux of the coils. So an EMF is induced, therefore inducing a current.