Question

Which of the following is/are true for an ideal step-down transformer?

• A. Primary voltage < Secondary voltage
• B. Number of turns in primary coil > Number of turns in secondary coil
• C. Primary current < Secondary current
• D. Power in primary coil < Power in secondary coil

Answer 1

Answer: (B), (C)

The correct options are
B Number of turns in primary coil > Number of turns in secondary coil
C Primary current < Secondary current

In a step-down transformer, output voltage is less than the input voltage i.e. secondary voltage is less than the primary voltage.
Also, for any transformer
$\frac{\text{Secondary voltage}}{\text{Primary voltage}}=\frac{\text{Number of turns in secondary coil}}{\text{Number of turns in primary coil}}$
Clearly, number of turns in secondary coil is less than that in primary coil.
In case of ideal transformer, power is same in both the coils, so option (d) is incorrect.
Since, power is same in both coils,
Power = $V_p\times i_p$ = $V_s\times i_s$
Since, $V_p$ > $V_s$ $\Rightarrow$ $i_s$ > $i_p$