If \( N_s \) is the number of turns in the secondary coil and \( N_p \) is the number of turns in the primary coil, which of the following is true for a step-down transformer?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( N_s\lt N_p \)
In a transformer the voltage changes in the ratio of the numbers of turns, \( V_s/V_p=N_s/N_p \). A step-down transformer gives an output voltage lower than the input voltage.
Option (1) \( N_s\gt N_p \) — Incorrect. More turns in the secondary give \( V_s\gt V_p \). The voltage is stepped up, so this is a step-up transformer.
Option (2) \( N_s=N_p \) — Incorrect. Equal numbers of turns give \( V_s=V_p \), so the voltage is neither stepped up nor stepped down.
Option (3) \( N_s\lt N_p \) — Correct. With fewer turns in the secondary, the ratio \( N_s/N_p \) is less than 1. So \( V_s\lt V_p \). The voltage is stepped down and the current is increased.
NCERT (2026-27):
Transformers – “If the secondary coil has less turns than the primary (Ns < Np), we have a step-down transformer. In this case, Vs < Vp and Is > Ip. That is, the voltage is stepped down, or reduced, and the current is increased.”