Question { Bhel, 15166 }

how can you prove that in CE configuration a transistor has
180 degree phase shifted output

Answer

Before reading my answer,i ask u 2 refer transistor biasing
circuit.

If u look at the o/p:
o/p eqn. can be written as:
Vce=Vcc-(Ic*Re);

As i/p increases,Ib(which wil b the i/p in CE Mode wil
increase so Ic increases so drop across Re increases
resulting in decreased Vce.

If u take a sinusoidal i/p,Correspondingly u add all d
points u wil get a 180 phase shift

Question { Birla, 20001 }

WHY POLARITY TEST OF CT IS VERY IMPORTANT IN SWITCHGEAR

Answer

Polarity Test is needed for Ct's because if polarities are not properly matched (Subtractive generally),relays which were based on connections of ct will maloperate(E/L Stability)and hence the lines will unnecessary trip....