$A$ transformer is used to light a $100\,W$ and $110\,V$ lamp from a $220\,V$ main. If the main current is $0.5\,A$, the efficiency of the transformer is approximately .....$\%$

An ideal transformer has $100$ turns in the primary and $250$ turns in the secondary. The peak value of the $ac$ input voltage is $28 \, V$. The r.m.s. secondary voltage is nearest to.....$V$

The number of turns in the primary and secondary coils of a transformer are $50$ and $200$ respectively. If the current in the primary coil is $4 \,A$, then the current in the secondary coil is: (in $\,A$)

The number of turns in the primary coil of a transformer is $200$ and the number of turns in the secondary coil is $10$. If $240 \ V$ $AC$ is applied to the primary,the output from the secondary will be......$V$.

In a transformer,the mutual inductance between the primary and secondary coils is $0.5 \ H$. The resistances of the primary and secondary coils are $20 \ \Omega$ and $5 \ \Omega$ respectively. To induce a current of $0.4 \ A$ in the secondary coil,what is the required rate of change of current in the primary coil in $A/s$?

An ideal transformer converts $220 \ V$ $AC$ to $3.3 \ kV$ $AC$ to transmit a power of $4.4 \ kW$. If the primary coil has $600$ turns,then the alternating current in the secondary coil is: