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Which of the following devices may be used to step up the...

Which of the following devices may be used to step up the voltage in a d.c. circuit?

A.

a step-up transformer

B.

a d.c. generator

C.

a wattmeter

D.

an induction coil

Correct answer is D

An induction coil is a transformer for producing high-voltage alternating current from a low-voltage direct current, consisting essentially of two concentric coils with a common soft-iron core, a primary coil with relatively few windings of heavy wire, and a secondary coil with many turns of fine wire. Excitation of the primary coil by rapidly interrupted or variable current induces high voltage in the secondary coil.