Question

In a transformer,number of turns in the primary are 140 and that in the secondary are 280.If current in primary is 4 A,then that in the secondary is

• A. 4A
• B. 2A
• C. 6A
• D. 10A

Answer 1

The correct option is B 2A

Answer is B.
A transformer takes high-voltage electricity with a small current and changes it into low-voltage electricity with a large current, or vice versa. That is, step up or step down the voltage in a circuit. A step-up transformer turns low-voltage electricity into high-voltage electricity while dropping the current. A step-down transformer changes high-voltage electricity into low-voltage electricity.If we change the number of turns in the coils we change the induced emf. This allows us to change (transform) the voltage from the primary to the secondary coil.The Turns Rule is:
Ns/Np=Vs/Vp
Where,
Ns = number of turns on the secondary coil
Np = number of turns on the primary coil
Vs = voltage across the secondary coil
Vp = voltage across the primary coil
The voltage and current are inversely proportional. So the Turn's rule can be written as Ns/Np=Ip/Is.
In this case, number of turns in the primary are 140 and that in the secondary are 280. The current in primary is 4 A.
So, 280/140 = 4/x.
x = 2 A.
Hence, the current in the secondary coil is 2 A.