The quantity that remains unchanged in a transformer is:

For an ideal transformer,if $N_S > N_P$,then . . . . . . .

$A$ transformer is used to step up an alternating e.m.f. of $220 \ V$ to $4.4 \ kV$ to transmit $6.6 \ kW$ of power. The primary coil has $1000$ turns. The current rating of the secondary coil is (Transformer is ideal): (in $A$)

In a transformer,the number of turns in the primary coil is $140$ and that in the secondary coil is $280$. If the current in the primary coil is $4 \ A$,then the current in the secondary coil is (in $A$):

$A$ step-down transformer transforms $220 \text{ V}$ to $11 \text{ V}$. If the currents in the primary and secondary coils are $5 \text{ A}$ and $90 \text{ A}$ respectively,the efficiency of the transformer is: (in $\%$)

The primary and secondary coils of a transformer have $50$ and $1500$ turns respectively. If the magnetic flux $\phi = \phi_0 + 4t$,where $\phi$ is in webers,$t$ is time in seconds and $\phi_0$ is a constant,the output voltage across the secondary coil is......$V$