Problem #0273 Electricity & Magnetism Sub-menu Problem #0275 Chapters Chapters

544.

Problem 39.41 (RHK)

We have to show that the current in the primary circuit remains unchanged if a resistance is connected directly across the generator, the transformer and the secondary circuit being removed. That is

In this sense we see that a transformer not only “transforms” potential differences and currents but also resistances.

Solution:             Click For PDF Version

In an ideal transformer the secondary emf (secondary circuit being open) and the primary emf are related to each other through (number of turns in the secondary coil) and (number of turns in the primary coil) as

When a resistive load R is connected across the secondary windings, there will be a current flow in the secondary given by

The power dissipation in the secondary will be

This power will be drawn from the generator feeding the primary coil of the transformer. A current will begin to flow in the primary, which can be determined from the relation

where

Thus if the transformer and the secondary circuits are removed and a resistive load is applied across the generator the same amount of current equal to will be drawn from the generator.