Unit 4

Chapter 1 : Electromagnetic induction

Dr. Mohamed Adel

Chapter 1 : electromagnetic, mutual and self inductance.

- Scientist Oersted discovered that magnetism could be produced by an electric current passes

through a conductor.

- Scientist Faraday discovered that electric current could be produced by using magnetism and

he called this phenomenon (electromagnetic induction)

Electromagnetic induction and faraday's

law

Faraday experiments:

Steps:

1- He made a cylinder coil of insulated copper wire such that the coil turns were separated

from each other.

2- He connected the 2 terminals of the coil to a sensitive galvanometer having its zero

reading at the midpoint of its graduated scale.

3- When he plunged a magnet into the coil (Observation) the pointer of the galvanometer

was deflected momentarily in a certain direction 4- When he remove the magnet from the coil (Observation) the pointer of the

galvanometer was deflected in the opposite direction 5- When he fixed the magnet and he moved the coil towards or away from the magnet he

found the same observations

6- When he fixed the magnet inside the coil he found that the pointer of the galvanometer

doesn’t change

Conclusion:

- An electromotive force and an electric current are induced in the coil when the magnet flux

lines cut the coil when the magnet is plunged into or removed from the coil.

1- The magnitude of e.m.f. is direct proportional with the rate by which the conductor cuts

the line of magnetic flux linked with it e. m. f. α ∆φm

∆t

(ɸm is the variation in the magnetic flux intercepted by the conductor in interval ∆t)

- This rate depend on the speed of the magnet and the magnetic flux density

∆ɸm = B .A measured by Weber ( B = magnetic flux density )

2- The magnitude of emf depends on the number of turns of the coil ( N ) which cut the

magnetic flux (emf α N)

𝐞.𝐦. 𝐟. = −𝐍 ∆ɸ𝐦

∆𝐭 …………….. Faraday’s Law

(Volt) or (Weber/sec) or (Tesla.m2 /s)

Faraday Law

Illustrating video

Lenz Rule

𝐞.𝐦. 𝐟. = −𝐍 ∆ɸ𝐦

∆𝐭 …………….. Faraday’s Law

(Volt) or (Weber/sec) or (Tesla.m2 /s)

- This negative sign indicates that the direction of the induced electric current tends to

oppose the cause producing it ( Lenz’s rule )

Illustrating video

Lets Define Things

Faraday’s Law of electromagnetic induction: the induced electromotive force which is

generated in a coil by the electromagnetic induction is direct proportional with the time rate by

which the coil cut (linked with) the lines of magnetic flux and the number of turns of the coil

Lenz’s rule: the induced current must be in a direction such as to oppose the change producing

it.

Solved Example(1)

Solved Example(2)

Illustrating videos