A piece of copper and other of germanium are cooled from the room temperature to 80 K, then (a) resistance of each will increase (b) resistance of copper will decrease (c) resistance of copper will increase while that of germanium will decrease (d) resistance of copper will decrease while that of germanium will increase

 Q:-

A piece of copper and other of germanium are
cooled from the room temperature to 80 K, then
(a) resistance of each will increase
(b) resistance of copper will decrease
(c) resistance of copper will increase while that of
germanium will decrease
(d) resistance of copper will decrease while that of
germanium will increase

 

 sol:- 

Copper is a conductor, so, its resistance
decreases on decreasing temperature as thermal agitation
decreases whereas germanium is semiconductor,
therefore, on decreasing temperature resistance increases

Q:- 

The core of a transformer is laminated because

a) the weight of the transformer may be reduced

 
(b) rusting of the core may be prevented

(c) ratio of voltage in primary and secondary may be
increased

 
(d) energy losses due to eddy currents may be minimised

 

Solution: When there is change of flux in the core of a
transformer due to change in current around it, eddy
current is produced. The direction of this current is
opposite to the current which produces it, so it will
reduce the main current. We laminate the core so that
flux is reduced resulting in the reduced production of
eddy current.

 

SOL:-