A transformer cannot raise or lower the voltage of a D.C. supply because

A. There is no need to change the D.C. voltage
B. A D.C. circuit has more losses
C. Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
D. None of the above

Answer: C
  • The transformer works on the principle of mutual induction, for which current in one coil must change uniformly
  • If dc supply is given, the current will not change due to constant supply and transformer will not work
  • Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero
  • Practically winding resistance is very small
  • For dc, the inductive reactance is zero as dc has no frequency
  • So total impedance of winding is very low for dc
  • Thus, winding will draw very high current if dc supply is given to it
  • This may cause the burning of windings due to extra heat generated and may cause permanent damage to the transformer.
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