Electromagnetic Induction

Question 1

Define Magnetic Flux.

Define its unit.

Answer 1

Product of flux density and perpendicular area.

Weber (Wb) -> flux passing through an area of 1m^2 at B = 1T. NmA^-1

Question 2

Define Magnetic Flux Linkage.

Answer 2

Product of magnetic flux and number of turns in a coil (of an electromagnet).

Question 3

Define Faraday’s Law.

Answer 3

Magnitude of an induced EMF is proportional to the rate of change of magnetic flux linkage.

Question 4

Define Lenz’ Law.

Answer 4

The direction/signage of an induced EMF opposes the flux change causing it.

Question 5

State and explain the changes to magnetic field strength and I(rms) when an iron core is added to a solenoid. [5]

Answer 5

• for equal I, iron has a higher induced EMF (dNø/dt) than air;
• therefore strength of magnetic field increases;
• therefore induced EMF in solenoid increases;
• Induced EMF opposes applied EMF;
• therefore I(rms) decreases;

Question 6

Why magnet falls more slowly in conduction tube: [4]

Answer 6

• as magnet falls, flux intersects tube;
• eddy currents produced in conducting tube;
  * either*
• eddy currents do work by heating tube;
• less E available for Ek, therefore lower terminal velocity;
  * or*
• eddy currents produce magnetic field that opposes magnet’s direction of motion;
• magnet has a < g and a lower terminal velocity;