Question

A step-up transformer has 300 turns on its primary coil and 90,000 turns on its secondary coil. If the current flowing through the secondary is .5 amps, what is the current flowing in the primary?

Answer 1

from conservation of energy theorem,

energy consumed by secondary coil = energy consumption by primary coil

or, $V_sI_s=V_pI_p$......(1)

also we know, $\frac{N_s}{N_P}=\frac{V_s}{V_p}$ ......(2)

from equation (1) and (2),

$\frac{I_p}{I_s}=\frac{N_s}{N_p}$

here N, V and I have their usual meanings.

here, $N_s=90000,N_p=300,I_s=0.5A$

then, $I_p$/0.5 =90000/300

or, $I_p$ = 0.5 × 300 = 150A

hence, 150A current flowing through primary coil.