$A$ 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 .....$\%$

If a transformer of an audio amplifier has an output impedance of $8000 \ \Omega$ and the speaker has an input impedance of $8 \ \Omega$,what should be the ratio of the primary to secondary turns of this transformer connected between the amplifier output and the loudspeaker?

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......$V$

$A$ transformer consists of $500$ turns in the primary coil and $10$ turns in the secondary coil with a load of $10\, \Omega$. Find the current in the primary coil when the voltage across the secondary coil is $50\, V$. (in $A$)

$A$ step-down transformer reduces the voltage of a transmission line from $2200 \,V$ to $220 \,V$. The power delivered by it is $880 \,W$ and its efficiency is $88 \%$. The input current is

Write the working procedure of a transformer.