Question

Draw a labelled diagram of a step-up transformer and explain how it works.

Answer 1

Step-up transformer: The step-up transformer is used to change a low voltage alternating e.m.f. to a high voltage alternating e.m.f. of same frequency.

Working: When the terminals of primary coil are connected to the source of alternating e.m.f., a varying current flows through it which also produces a varying magnetic field in the core of the transformer. Thus, the magnetic field lines linked with the secondary coil vary and induce an e.m.f. in the secondary coil. The induced e.m.f. varies in the same manner as the applied e.m.f. in the primary coil varies, and thus, has the same frequency as that of the applied e.m.f.

The magnitude of e.m.f. induced in the secondary coil depends on the 'turns ratio' and the magnitude of the applied e.m.f.

For a transformer,

`("E.m.f. across the secondary coil" ("E"_"s"))/("E.m.f. across the primary coil"("E"_"p")) =  ("Number of turns in the secondary coil" ("N"_"s"))/("Number of turns in the primary coil" ("N"_"p"))` =  Turns ratio (n)