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