A 100% efficient ideal transformer has 400 turns on its primary coil and 100 turns on its secondary coil. The input voltage across the primary coil is 240 V. An output current of 2.0 A flows in the secondary coil. What are the output voltage across the secondary coil, the input current in the primary coil, and the output power of the transformer?

Answer:

27) B

This question requires us to use the formula:
Turns on primary coil

Voltage on primary coil

Turns on secondary coil
Voltage on secondary coil

400 240

100
Voltage on secondary coil
100 x 240
voltage on seconday coil =
= 60 V
400
So, output voltage = 60 V
To find to input current, we use the following formula:

Current in primary coil current in secondary coil

Voltage in secondary coil voltage in primary coil
current in secondary coil x Voltage in secodnary coil voltage in primary coil
Current in primary coil =
Current in primary coil =
2 x 60 240
= 0.5 A
Power = Voltage x Current
Output power = 60 x 2 = 120 W
So the answer is B.