Question:easy

A transformer has 50 turns in the primary and 100 in the secondary. What will the voltage across the secondary be if the primary is connected to a 220 V DC supply?

Show Hint

Transformers need changing flux; steady DC gives no induced EMF in the secondary.
Updated On: Jul 2, 2026
  • 440
  • 220
  • 110
  • Zero Volts
Show Solution

The Correct Option is D

Solution and Explanation

The transformer relation $\dfrac{V_s}{V_p}=\dfrac{N_s}{N_p}$ is derived assuming a sinusoidal (AC) source, where both primary and secondary voltages are the induced EMFs from a common alternating flux. That derivation breaks down for DC.

With a 220 V DC supply, once the transient dies out the primary current is steady, so the core flux settles to a constant value. A constant flux has zero time derivative, and Faraday's law gives an induced secondary EMF of $V_s=-N_s\,d\Phi/dt=0$.

Therefore, plugging into the turns-ratio formula is invalid; the physically correct answer is that the steady-state secondary voltage is zero. (Only during the brief switch-on transient would a momentary spike appear.) This corresponds to option (D).

\[\boxed{V_s=0\,\text{V (DC)}}\]
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