Question

A 100% efficient transformer has 100 turns in the primary and 25 turns in its secondary coil. If the current in the secondary coil is 4 amp, then the current in the primary coil is [MP PMT 1990]
A) 1 amp B) 4 amp C) 8 amp D) 16 amp

Answer 1

Number of turns in the primary , Np = 100
Number of turns in the secondary , Ns = 25
Current in the secondary coil ,is = 4 amp
we have to find out current in the primary coil ,ip = ?

∵ Ns/Np = Vs/Vp
Also , Vs × is = Vp × ip
Then, Ns/Np = ip/is
⇒100/25 = ip/4
⇒4 × 4 = ip
⇒ ip = 16 amp

Hence, current in the primary coil is 16 amp
So, option (D) is correct.

Answer 2

It should be 1 amp.

Np/Ns = Vp/Vs

Vp/Vs = Is/Ip

Np/Ns = Is/Ip

100/25 = 4/Ip

Ip = (4 x 25)/100

Ip = 100/100

Ip = 1 amp