Which is a characteristic of a step-up transformer?
a: there are fewer loops in the secondary coil than in the primary coil.
b: it converts direct current into alternating current.
c: the voltage of the secondary coil is greater than that of the primary coil.
d: the voltage of the secondary coil is less than that of the primary coil.

d:The voltage of the secondary coil is less than that of the primary coil.

The correct option is (c).

Explanation:

Transformer is a device which increases or decrease the voltage of an  alternating current. The transformer consists of the secondary coil and the primary coil. It is used to transfer electrical energy by means of changing magnetic field.

Step-up transformer is used when the voltage of an alternating current is increased. The voltage in secondary coil is greater than that of the primary coil in this transformer.

Step-down transformer is used when the voltage of an alternating current is reduced.

Therefore, the correct answer is (c).