Page 63 - Basic Electrical Engineering

FRHR states that when we stretch the three fingers of the right hand
perpendicular to each other, if the fore finger points towards the flux lines
from North pole to South pole, and the thumb shows the direction of

movement of the conductor, then the middle finger will represent the
direction of the induced EMF or current in the conductor. In Fig. 1.11 (b) is

shown the direction of the induced EMF in coil-side ab of the rotating coil
abcd. This coil side is shown going upwards. The magnetic field direction is

from North pole to South pole. Hence, the direction of the induced EMF will
be from b to a as determined by applying FRHR. The stronger the magnetic

field is, the more will be the magnitude of EMF induced. The more the speed
of rotation of the coil is, the more will be the magnitude of the EMF induced.

This is because will increase if both ϕ as well as the rate of change of

linkage of ϕ are changed. The magnitude of the EMF induced will also be
directly proportional to the number of turns of the rotating coil, or the number

of coils connected in series. The EMF induced can also be considered in
terms of flux cut by a conductor (coil side) per second.

Here in Fig. 1.11, the number of poles is two. We can also have four poles,
six poles, etc. When a conductor rotates in such magnetic field, it cuts the

lines of force. The number of lines of force cut by a conductor in one
revolution, when there are two poles, is 2 ϕ Webers, where ϕ is the flux per

pole. If there are say P number of poles, flux cut by a conductor in one
revolution will be P ϕ Webers. If the coil makes ‘n’ revolutions per second,
the time taken by a conductor to make one revolution will be 1/n seconds.

Thus, flux cut per second will be the EMF induced, e which is

or,