In your model is coil B the primary coil or the secondary coil how do you know

Answer

If Alternating voltage is applied to Coil B then it is said to be primary coil

Explanation

A transformer is a device which is used for reducing or increasing the voltage of an alternating current. It consists of two coils which are not connected to each other.

Primary coil

The coil to which the alternating voltage is supplied is called the primary coil. The alternating potential difference of this coil results in an alternating current in the primary coil and produces a changing magnetic field around it.

Secondary Coil:

Due to changing magnetic flux of around the primary coil, an alternating current is induced in second coil and an alternating voltage is induced in second coil this coil is known as secondary coil.

There are two types of transformer

step up transformer

In step up transformer, number of loops in the secondary coil is more than the number of loop in primary Coil. Therefore voltage across secondary coil will be more.

If the given model is step up transformer then coil B will have more number of loops than coil A. And coil A will be connected to Alternating voltage. In this Case Coil A will said to be primary coil and Coil B will be Secondary coil

step down transformer

In step down transformer, number of loops in the secondary coil is less than number of loop in primary coil. Therefore voltage across secondary coil will be less.

If the given model is step down transformer then coil B will have less number of loops than coil A and coil A will be connected to Alternating voltage. In this Case Coil A will said to be primary coil and Coil B will be Secondary coil