Magnetic flux

Question 1

What is magnetic flux

Answer 1

magnetic flux density * cross sectional area perpendicular to field direction - webers

Question 2

What is one weber

Answer 2

the unit of magnetic flux, one tesla metre 1 Tm

Question 3

What is magnetic flux linkage

Answer 3

N*magnetic flux where N is the number of turns. It depends on
- flux density
- orientation of coil and flux lines
- the coils area
- the number of turns

Question 4

What are weber turns?

Answer 4

The unit of magnetic flux linkage

Question 5

How does EM induction work?

Answer 5

• when a charge is moving perpendicular to a field experiences a force BQv
• The electrons would move to one end of the wire when the wire moves perpendicular to the magnetic field.
• This leaves one end of the wire negatively charged overall and the other positively charged.
• This then creates a PD

Question 6

what is Faradays law?

Answer 6

The induced EMF in a coil equals the rate of change of magnetic flux.

Question 7

What is Lenz’s law?

Answer 7

The direction of the induced EMf causes effects that oppose the charge producing it.

Question 8

Why does Lenz’s law happen?

Answer 8

When the south end of a magnet is pushed into the coil, a current is induced, which becomes an electromagnet. If the south pole of the electromagnet faces the moving magnet, the poles repel and work must be done to keep pushing the magnet into the coil of wire. If it didn’t occur, the magnet would accelerate exponentially.

Question 9

What is an Eddy currrent?

Answer 9

Circulating electric currents flowing in the plane of the metal.

Question 10

What causes Eddy currents?

Answer 10

The change of flux linkage when the metal moves perpendicular to the field, and the currents flow in directions to oppose the motion creating them

Question 10

How do guitar pickups work?

Answer 10

• When strings are plucked, they vibrate directly above the pickups.
  -The pickups are tightly wrapped bar magnets.
• the vibrating string causes vibrations in the magnetic field.
• the change is converted into an emf and amplified.

Question 10

What is the induced emf in a credit card

Answer 10

emf = B * dA/dt

emf = Blv

Question 11

what is power in a magnetic field

Answer 11

p = emf * I

or P = (blv)I = (Bil)v

Question 12

What is the max emf in a rotating magnetic field?

Answer 12

Emf = BAN * omega