Concept:Alternating current (AC) devices rely on a changing magnetic flux to operate, while direct current (DC) devices work with a steady current flow.
Explanation:A step-up transformer increases voltage by electromagnetic induction, which requires a continuously changing current.
Direct current produces a constant magnetic field, so a transformer cannot work with DC.
Therefore, a step-up transformer is specifically designed to operate only with alternating current.
An induction coil uses interrupted DC, not pure AC.
A moving coil galvanometer measures direct current.
A lead-acid accumulator stores and supplies direct current.
Thus, among the given options, only the step-up transformer is exclusively associated with alternating currents.
Answer:A. Step-up transformer