A transformer cannot be used with a direct current supply because
- 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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