Page 157 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

or, e = N (Ø2 -Ø1)volt

t
putting the above expression in its differential form, we get
e =d (NØ) =N dØ
dtdt

Usually a mines sign is given to the right hand expression to signify the fact that the induced emf , set up current in
such a direction that magnetic effect produced by it opposes the very cause producing it( according to the Lenz’s
law)

- N d∅voltdt
Direction of induced emf & current
The direction of induced emf /current may be found easily by applying following two rules
Flemings right hand rule

Lenz’s law
Flemings ruleis used where induced emf due to flux cutting ie, dynamically induced emf.And Lenz’s law where it
is change by flux linkages ie, statically induced emf.

Flemings right hand rule
This rule state that, If you spread your right hand in such a way that the thumb, fore finger and middle finger are
right angle to each other. The thumb direct to the motion of the conductor, the fore finger direct to the direction of
magnetic flux and then the middle finger indicates the direction of induced emf / current.
Lenz’s law
This law formulated by Lenz’s in 1835. This law states, in effect, that electro magnetically induced current always
flows in such a direction that the action of the magnetic field set up by it to oppose the very cause producing it.
An induced current will flow in such a direction so as to oppose the very cause which produces it’

AC Fundamental
Alternating current
An alternating current circuit is one in which the direction and amplitude of the current flow change at regular
intervals .The polarity of an AC source changes at regular intervals resulting in reversal of the circuit current
flow .Alternating current usually changes in both value and direction. The current increases from zero to some
maximum value and then drop back to zero as it flows in one direction. This same pattern is then repeated as it
flows in the opposite direction.AC is produced by alternator

Direct Current
Direct current is the current that flows only in one direction in a circuit. The polarity of a DC source remains fixed
and current flows in one direction only. DC is produced by Cells &Batteries , DC generator etc.

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CITS : Power - Electrician & Wireman - Lesson 26-29