A transformer cannot be used with a direct current supply because
Correct answer: B. steady direct current gives no changing flux, so no emf is induced in the secondary
- A. direct current is too dangerous
- B. steady direct current gives no changing flux, so no emf is induced in the secondary
- C. the core would melt
- D. direct current cannot flow in a coil
Explanation
Induction requires a changing flux, and a steady current produces a steady flux, so the secondary voltage is zero except at the instants of switching on and off. Connecting a transformer to a DC supply also risks burning out the primary, since only its low resistance and not its inductive reactance limits the current. This is a fundamental reason the grid uses alternating current.
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About Transformers
Transformers transfer alternating electrical energy between coils by mutual induction, with voltage ratio determined by the turns ratio. The topic covers step-up and step-down transformers, current changes, ideal power conservation and practical losses such as heating and flux leakage. A transformer requires changing magnetic flux, so it does not operate with steady direct current.
Practise Electromagnetic Induction
288 free Electromagnetic Induction MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
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