Question

(8) When a DC voltage is applied to the transformer instead of AC voltage, then its efficiency
a) increase
b) decrease
(c)remàin same
(d) becomes zero
l​

Answer 1

Explanation:

If DC supply is given to the primary coil of Transformer then DC current flows through primary winding which is constant (time invarient). For production of emf in any winding, the current flowing through that must be sinusoidal.

Induced emf  E=L×(dI/dt).

So in the given case ie, for DC input, no emf produced in primary winding. So net voltage in the primary winding will be (Vin-0) more due to which primary winding draws more current which leads to burning of winding.

Answer 2

Answer:

This answer will come from the volt-sec balance equation. From Faraday's law we know that e=L*d(phi)/dt so after some mathematical manipulation and integrating both sides we will get to phi= Integration of voltage with time. As time increase the flux will keep on increasing till the max capacity the material to hold the flux reaches. Once the material crosses the barrier flux holding capacity it looses its magnetic properties and circuit will be a simple short circuit.