(i) The number of turns in the secondary coil of a transformer is 20 times than that in a primary coil. If the power fed to the primary coil is 100 W (assume no energy loss), then what is the power output at the secondary coil ?

1. 5 W
2. 100 W
3. 2000 W
4. 4000 W

(ii) If the primary coil of the above transformer is supplied with 10 V, what is the voltage of the secondary coil ?

1. 0.5 V
2. 10 V
3. 200 V
4. 100 V

(i) 100 W

(ii) 200 V

Reason —

(i) In an ideal transformer (no energy loss), the input power equals output power. Therefore, even though the number of turns changes, the power remains the same.

Hence, the secondary coil also delivers 100 W.

(ii) Given,

• Ratio of number of turns in the secondary coil to the primary coil = 20
• Voltage of the primary coil = 10 V

In a transformer, voltage is proportional to the number of turns i.e.,

$\dfrac{\text {Voltage of the primary coil}}{\text {Voltage of the secondary coil}} = \dfrac{\text {Number of turns in the secondary coil}}{\text {Number of turns in the primary coil}} \\[1em] \Rightarrow \text {Voltage of the secondary coil} = \dfrac{\text {Number of turns in the primary coil}}{\text {Number of turns in the secondary coil}} \times \text {Voltage of the primary coil} \\[1em] = 20 \times 10 \\[1em] = 200\ \text V$

Hence, the voltage of the secondary coil is 200 V.