The quantity that remains unchanged in a transformer is:

$A$ transformer has an efficiency of $80 \%$. The input power to the primary coil is $4 \text{ kW}$ at a voltage of $100 \text{ V}$. If the secondary voltage is $200 \text{ V}$,what are the primary and secondary currents,respectively?

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

In an ideal step-down transformer, out of the following quantities, which quantity increases in the secondary coil?

$A$ step-down transformer has a turns ratio of $20:1$. If $8 \, V$ is applied across a $0.4 \, \Omega$ secondary coil, then the primary current will be: (in $ \, A$)

$A$ step-down transformer is connected to a $2400 \, V$ line, and $80 \, A$ of current is found to flow in the output load. The ratio of the turns in the primary and secondary coil is $20 : 1$. If the transformer efficiency is $100\%$, then the current flowing in the primary coil will be: (in $A$)