State the underlying principle of a transformer and obtain the expression for the ratio of secondary to primary voltage in terms of the three
(i) number of secondary and primary winding send
(ii) primary and secondary currents.

Explanation

Principle of a transformer : When the alternating current flows through the primary coil and EMF is induced in the neighbouring (secondary) coil
(i) Let `(d phi)/(d t)` be the rate of change of flux through each turn of the primary and the secondary coil
`(epsilon_(1))/(epsilon_(2)) = -N_(1).(d phi)/(d t)//-N_(2).(d phi)/(d t) = (N_(1))/(N_(2))`
or `(V_(1))/(V_(2)) = (N_(1))/(N_(2))` ...(i)
(ii) But for an ideal transformer , `V_(1)I_(1) = V_(2)I_(2)`
`(V_(1))/(V_(2)) = (I_(2))/(I_(1))` ...(ii)
from equation (i) and (ii)
`(V_(1))/(V_(2)) = (N_(1))/(N_(2)) = (I_(2))/(I_(1))`