The number of turns in the primary coil when the transformer is used to step down the AC emf from 220 V to 6 V, assuming that it has 18 turns in its secondary coil is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 660
For an ideal transformer the voltage per turn is the same in both coils, so the turns ratio equals the voltage ratio.
\( \displaystyle \frac{N_p}{N_s} = \frac{V_p}{V_s} \)
\( V_p = 220\,\mathrm{V} \)
\( V_s = 6\,\mathrm{V} \)
\( N_s = 18 \)
\( \displaystyle N_p = N_s \times \frac{V_p}{V_s} = 18 \times \frac{220}{6} = 660 \)