A step-up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the number of turns in the primary is 75, the number of turns in the secondary is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 1500
In a transformer, the same flux links every turn of both coils. So the voltages are in the ratio of the numbers of turns, \( V_s/V_p=N_s/N_p \). A step-up transformer has more turns in the secondary than in the primary.
\( \begin{aligned} N_s &= N_p\,\frac{V_s}{V_p} \\ &= 75\times\frac{2400\,\mathrm{V}}{120\,\mathrm{V}} \\ &= 1500 \end{aligned} \)