(a) In which direction will the coil begin to rotate when current is passed through the coil in direction ABCD by connecting a battery at the ends A and D of the coil?
(b)Why is a commutator necessary for the continuous rotation of the coil?
(c) Complete the diagram with the commutator, etc. for the flow of current in the coil.
Solution:
(a) The coil starts to rotate in the opposite direction as the clock.
(b) After half revolution, the arms AB and CD are swapped, reversing the direction of torque on the coil. A commutator is required to keep the coil rotating in the same direction by reversing the direction of current in the coil after each half rotation. As a result, the commutator is required for the coil to rotate continuously.
(c) The complete diagram is given below –
and 
, internal resistance 
and 
, connected in parallel. The equivalent emf of the combination is- (A) 
(B) 
(C) 
(D) 
and 
are collinear, prove that 
and 
be three points such that area of a 
is 4 sq units, find the value of 
.
and 
is 35 sq units.
and 
are collinear.
and 
are collinear.
and 
are collinear.
and 