Electromagnetic Induction

Question 1

Factors affecting induced current for a straight wire.

Answer 1

• Magnitude of magnetic flux density.
• Length of the wire in field.
• Speed of movement of wire.

Question 2

Factors affecting induced current for a coil of wire.

Answer 2

• Magnitude of magnetic flux density.
• Cross-sectional area of the coil.
• The number of turns of wire.
• The rate at which the coil turns in the field.

Question 3

When a coil is inside a magnetic field….we say it has?

Answer 3

We say flux links the coil (field lines link the coil).
OR
We say it has flux linkage.

Question 4

When a conductor is not part of a complete circuit…what is induced?

Answer 4

e.m.f (negative charge will accumulate at one end of the conductor, leaving the other end positively charged).

Question 5

Why is e.m.f the correct term to use for what is induced in a conductor that is not part of a complete circuit.

Answer 5

Cuz if the ends of the conductor are connected to a component, such as a lamp, that part of the conductor serves as a source of electrical energy.

Question 6

What causes electrons to move in a conductor, when current is induced?

Answer 6

Moving the conductor is equivalent to giving an electron within the conductor a velocity in the direction of this motion. (The electron is in an external magnetic field and hence experiences a magnetic force Bev).

Question 7

Equation to find magnetic flux through an area.

Answer 7

Magnetic flux (phi) = BA (where B is the component of magnetic flux density perpendicular to the area).

When at an angle ~> BAcos0

Question 8

For a coil with N turns , the magnetic flux linkage is…?

Answer 8

The product of magnetic flux and the number of turns. (N x phi).

Question 9

Unit of magnetic flux or linkage.

Answer 9

Weber (Wb).

Question 10

What is one weber?

Answer 10

This is the flux that passes through an area of 1m² when magnetic flux density is 1T. (1 Wb = 1 Tm²)

Question 11

An e.m.f is induced in circuit whenever there is a change in magnetic flux linking the circuit.

Answer 11

This can be done by :
•changing B
•Changing the area A of the circuit.
•Changing the angle.

Question 12

The idea of magnetic flux linkage states that….

Answer 12

If there is a change in the number of field lines which pass through a coil, an emf will be induced across the ends of the coil ( or current if the coil is part of a complete circuit).

Question 13

What is faraday’s law of e.m induction?

Answer 13

The magnitude of the induced e.m.f. Is proportional to the rate of change of magnetic flux Linkage.

Question 14

Equation for magnitude of induced e.m.f.

Answer 14

E = Δ(Nphi) /Δt.

Question 15

State Lenz’s law.

Answer 15

Any induced current or induced e.m.f. will be established in a direction so as to produce effects which oppose the change that is producing it.

Question 16

When the flux linking an area changes, we say….?

Answer 16

An induced e.m.f. is generated.

Question 17

In an a.c generator, at which position does the coil induce maximum e.m.f.?

Answer 17

When the coil is horizontal ( parallel to the field lines ). As at this point field lines are rapidly cut.

Question 18

When the flux linking the coil is maximum,……

Answer 18

The rate of change of flux is zero and so the induced e.m.f is zero.

Question 19

When the flux linking the coil is zero……

Answer 19

The rate of change of flux is maximum and so the induced e.m.f is also maximum.

Question 20

What is the effect of using soft iron in the core of a transformer?

Answer 20

It increases the amount of magnetic flux.