$A$ transformer has an efficiency of $80 \%$ and works at $10 \ V$ and $4 \ kW$. If the secondary voltage is $240 \ V$, then the current in the secondary coil 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:

$A$ transformer having an efficiency of $90 \%$ is working on a $200 \ V$ and $3 \ kW$ power supply. If the current in the secondary coil is $6 \ A$,the voltage across the secondary coil and the current in the primary coil respectively are:

Which of the following is correct for a real transformer?

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

Large transformers,when used for some time,become hot and are cooled by circulating oil. The heating of a transformer is due to: