SOLUTION

• A transformer works on the principle of mutual induction, in which you need a varying magnetic field in a winding to induce an EMF in the secondary winding.
• In DC generally change in frequency with respect to time is zero. If the primary of a transformer is connected to a d.c. supply, the primary will draw a steady current and hence produce constant flux. Consequently, no back e.m.f. will be produced.
• So a dc source cannot provide varying magnetic fields, hence mutual induction is not possible.
• The primary winding will draw excessive current due to the low resistance of the primary. The result is that the primary will overheat and burn out or the fuses will blow. Care must be taken not to connect the primary of a transformer across the DC supply.