Magnetic Fields & Alternating Currents

Question 1

State what is meant by a magnetic field.

Answer 1

It’s a region where force acts on a moving charge \ magnetic material

Question 2

Define magnetic flux density

Answer 2

Force per unit current per unit length on a wire placed perpendicular to the magnetic field.

Question 3

Define the tesla

Answer 3

Newton per ampere per metre, where the current is perpendicular to the magnetic field.

Question 4

State the two conditions that must be satisfied for a copper wire, placed in a magnetic field, to experience a magnetic force.

Answer 4

1. There must be a current in the wire
2. Wire must be at a non-zero angle to the magnetic field.

Question 5

State two situations in which a charged particle in a magnetic field does not experience a force.

Answer 5

1. particle is stationary
2. particle is moving parallel to the magnetic field

Question 6

Explain why the electrons follow a circular path when inside the region of the magnetic field

Question 7

Define magnetic flux.

Answer 7

magnetic flux density x area, where flux is normal to area and area is perpendicular to magnetic field

or

magnetic flux desnity x area x sinθ, where θ is the angle between flux direction and plan of area

Rule: Φ=BA

Question 8

State what is meant by the magnetic flux linkage of a coil.

Answer 8

The product of the magnetic flux desnity & area through a coil where the flux is normal to area, multiplied by the number of turns on the coil.

Rule: NΦ = BAN

Question 9

State faraday’s law of electromagnetic induction.

Answer 9

Induced E.M.F. is proportional to rate of change of magnetic flux linkage.

Question 10

State Lenz’s law of electromagnetic induction.

Answer 10

The law states that the direction of induced e.m.f. such as to produce effects that oppose the change that caused it.

Question 11

Explain what is meant by the root-mean-sqaure (r.m.s) value of an alternating current.

Answer 11

It’s the direct current that produces the same heating effect as the alternating current.

Question 12

State what is meant by rectification.

Answer 12

The conversion from a.c. to d.c.

Question 13

State what is meant by smoothing.

Answer 13

The Reduction in the variation of output voltage or current so that output does not fall to zero.

Question 14

Explain why the electrons follow a circular path when inside the region of the magnetic field.

Question 15

Explain the use of a uniform magnetic field and a uniform electric field for the selection of the velocity of charged particles.