Electromagnetism and Electromagnetic Induction

Question 1

Magnetic field

Answer 1

A region of space where a magnetic pole, a current-carrying conductor or a moving charge particle will experience a force.
(The direction of a magnetic field is the direction of force on a free north pole)

Question 2

Magnetic flux density, B*

Answer 2

The magnetic flux density of a magnetic field is defined as the force per unit length per unit current on a straight current-carrying conductor placed perpendicularly to the field. (For sintheta uw the angle to be 90 and so it has to be perpendicular)

Question 3

Magnetic flux

Answer 3

The PRODUCT of an area and the component of the MAGNETIC FLUX DENSITY PERPENDICULAR to that area. (for costheta uw the angle to be 0, so it has to be parallel to the NORMAL)

Question 4

Magnetic flux linkage

Answer 4

Magnetic flux linkage is the product of the magnetic flux passing through the coil and the number of turns on the coil, where magnetic flux is the product of an area and the component of the magnetic flux density perpendicular to that area.

Question 5

Faraday’s Law of Electromagnetic Induction*

Answer 5

Faraday’s Law states that the magnitude of the induced e.m.f. is directly proportional to the rate of change of the magnetic flux linkage.

Question 6

Lenz’s Law*

Answer 6

Lenz’s Law states that the INDUCED E.M.F. or CURRENT is in a DIRECTION so as to produce EFFECTS which OPPOSE THE CHANGE IN MAGNETIC FLUX LINKAGE

Question 7

How are Eddy currents produced

Answer 7

If the conductor is a solid plate, the rate of cutting is not the same over the whole plate, so different emf are induced in different parts of the plate. => eddy currents flow simultaneously along many different paths in swirls

This causes heat energy to be dissipated from the plate as Eddy currents flow in the conductor

Question 9

Helical path?

Answer 9

As the electron enters the magnetic field at an angle less than 90, it will experience a centripetal force provided by the magnetic force acting on it due to its component of velocity perpendicular to the magnetic field. This will result in a circular path.
However, the component of its velocity parallel to the magnetic field will be unaffected by the magnetic field. Hence, this component of velocity will remain constant, and the electron will move at a constant velocity in a direction parallel to the field lines.
A combination of the circular path and the constant velocity results in the helical path shown.