Question

If a step down transformer has 220 V coming into the primary coil of 30 turns and 140 V is coming out of
the second coil, how many turns in are in the secondary coil? (1 point)

30

19

0.05

7

Answer 1

To find the number of turns in the secondary coil of a transformer, we can use the transformer equation, which relates the primary voltage \( V_p \), secondary voltage \( V_s \), the number of turns in the primary coil \( N_p \), and the number of turns in the secondary coil \( N_s \):

\[
\frac{V_p}{V_s} = \frac{N_p}{N_s}
\]

Given:
- \( V_p = 220 \, V \)
- \( V_s = 140 \, V \)
- \( N_p = 30 \, \text{turns} \)

We want to find \( N_s \):

Rearranging the equation gives:

\[
N_s = N_p \times \frac{V_s}{V_p}
\]

Substituting the known values:

\[
N_s = 30 \times \frac{140}{220}
\]

Calculating:

1. Calculate \( \frac{140}{220} \):

\[
\frac{140}{220} = \frac{14}{22} = \frac{7}{11} \approx 0.6364
\]

2. Now calculate \( N_s \):

\[
N_s = 30 \times 0.6364 \approx 19.09 \, \text{turns}
\]

Since the number of turns must be a whole number, we can round \( 19.09 \) to \( 19 \).

Therefore, the number of turns in the secondary coil is **19**.