(b) If a piece of soft iron is placed inside the coil mentioned in part (a) and current is passed in the coil from a battery, what name is then given to the device so obtained?
(c) Give one use of the device mentioned in part (b).
Solution:
(a) A solenoid is a cylindrical coil with a diameter less than its length.
(b) The device obtained is known as an electromagnet.
(c) In an electric relay, an electromagnet is utilized.
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 
. for which the area of a ABC having vertices 
and 
is 35 sq units. for which the points 
and 
are collinear. for which the points 
and 
are collinear. for which the points 
and 
are collinear.
and 