Question

A transformer has 100 turns in the primary coil and 150 on the secondary. It is a

- step-down transformer.
- decreasing transformer.
- step-up transformer.
- increasing transformer.​

Answer 1

This transformer would be a step-up transformer.

Step-by-step explanation:

In a transformer, the primary coil is connected to the AC input while the secondary coil is connected to the AC output.

Let
`V_P` and
`N_P` denote the primary voltage (at the input) and number of turns in the primary coil.

Let
`V_S` and
`N_S` denote the secondary voltage (at the output) and the number of turns in the secondary coil.

Ideally, the voltage in each coil would proportional to the number of turns in that coil:

`\displaystyle (V_S)/(V_P) = (N_S)/(N_P)`.

For example, in this question,
`N_P = 100` (primary coil, connected to the AC input) whereas
`N_S = 150` (secondary coil, connected to the AC output.)

`N_S = 1.5 \, N_P`. Accordingly, the voltage in the secondary coil (AC output) would be approximately
`1.5` times the voltage in the primary coil (AC input):
`V_S = 1.5\, V_P`.

Hence, the secondary voltage of this transformer (AC output) would exceed the primary voltage (AC input.) This transformer would be a step-up transformer.