The input voltage and output voltage in the primary and secondary coils of a transformer are $250 V$ and $5 V$ , respectively. If the number of turns in the primary is $1000$ , find the number of turns in its secondary coil. Also mention, whether the transformer is a step-up one or a step-down one?

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Solution

Step 1: Given data
Input voltage $V_{p} = 250 V$
Output voltage $V_{s} = 5 V$
Number of turns in the primary $N_{p} = 1000$
Step 2: Finding the number of turns in its secondary coil
We know that, $\frac{N_{s}}{N_{p}} = \frac{V_{s}}{V_{p}}$ where $N_{s}$ and $N_{p}$ is number of turns in the secondary coil and primary coil respectively and $V_{s}$ and $V_{p}$ is voltage in the secondary and primary coil of the transformer.
Substituting the given values in
$\frac{N_{s}}{N_{p}} = \frac{V_{s}}{V_{p}}$
$\frac{N_{s}}{1000} = \frac{5}{250}$
Cross multiplying
$N_{s} = \frac{5}{250} \times 1000 N_{s} = 20$
Step 3: Finding the type of transformer
It is given that $N_{p} = 1000$ and $N_{s} = 20$
We know that when $N_{s} < N_{p}$ , the transformer is a step-down transformer.
Here, $20 < 1000$ so the transformer is a step-down transformer.
Hence, the number of turns in secondary coil is $20$ and transformer is a step-down transformer.

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