The instrument which works on the principle of mutual inductance is

$A$ transformer with $80 \%$ efficiency works at $4 \text{ kW}$ and $100 \text{ V}$. If the secondary voltage is $240 \text{ V}$, then the primary current is . . . . . . . (in $A$)

In a transformer,$220 \ V$ $AC$ voltage is increased to $2200 \ V$. If the number of turns in the secondary coil is $2000$,then the number of turns in the primary coil will be:

The self-inductance of two coils of a transformer is $20 mH$ and $30 mH$. What is the resistance between them?

In a step-up transformer,the turn ratio is $8:1$. $A$ $60\,Hz, 120\,V$ input is connected to its primary coil. The load resistance in the secondary coil is $10^4\,\Omega$. Find the current in the secondary coil.

$A$ $12\,V, 60\,W$ lamp is connected to the secondary of a step-down transformer, whose primary is connected to $AC$ mains of $220\,V$. Assuming the transformer to be ideal, the current in the primary winding is $..........\,A$.