Question

Primary coil of a step-up transformer has ______ number of turns than the secondary coil.
A. more
B. less
C. same
D. can’t say

Answer 1

A transformer is a device, which can step-up or step-down the given AC. This depends on the number of windings present in the coil. It follows a simple ratio. Using this ratio we can find if the transformer is a step-up or a step-down transformer.

Complete answer:
Transformer is known as an electrical device, which has the ability to vary the current. It works on the principle of mutual induction, where two coils are coupled, namely the primary and the secondary coil. The primary coil creates a varying magnetic flux due to the passage of AC current, which in turn induces an EMF on the secondary coil.
Consider the image shown below, if the number of windings in the primary coil is greater than the windings in the secondary coil, it is called a step-down transformer. Similarly, if the windings in the secondary coil are greater than the windings in the primary coil, it is called a step-up transformer.

Thus, the correct answer is B. less.

Additional Information:
An ideal transformer is a transformer in which there is no loss in magnetic flux or no flux leakage due to coupling and the inductance due to the winding of the coils is zero.
However, in reality, the winding of the coil has some impedance and there is magnetic flux leakage. To avoid this leakage of flux the coils are wound on a highly permeable magnetic core.

Note:
The efficiency of the transformer is said to depend on how well the input power is transferred as output power. Thus to increase the efficiency of the transformer, the windings of the coil must be increased and/or magnetic flux leakage must be reduced.