If constant current passes through the primary coil of a transformer, then the induced electromotive force (e.m.f.) across the secondary coil of the transformer will

Explanation

In a transformer, the induced electromotive force (e.m.f.) in the secondary coil is generated by the changing magnetic field created by the current in the primary coil. If the current through the primary coil is constant, it does not produce a changing magnetic field, and therefore, no e.m.f. is induced in the secondary coil. This is why the correct answer is Option A: be zero.Option B is incorrect because an increasing e.m.f. requires a change in the magnetic field, which is absent with a constant primary current.Option C is incorrect because the e.m.f. cannot decrease from zero when the magnetic field is not changing.Option D is incorrect because the result is well-known and not undetermined: a constant current leads to zero induced e.m.f.