A section of the circuit AB (see figure) absorbs 53 W of power when a current passes through it in the indicated direction. (a) We have to find the potential difference between A and B. (b) Assuming that the element C does not have any internal resistance, we have to find the emf. (c) We have to answer which terminal, left or right, is positive.

Solution:             Click For PDF Version

(a)

The section of the circuit AB shown in the figure absorbs 53.0 W of power when a current passes through it. We have to find the potential difference between A and B.

Joule heat in the resistance will be

Therefore, the power absorbed in the element C will be

(b) and (c)

As the device C is without internal resistance, it has to be a source of emf. The energy that is being absorbed by C is getting converted into chemical energy through the charging process. Therefore, the left terminal of C will be positive. The emf of C can be found from the relation

The potential difference A and B will, therefore, be

That is B is at , if A is at 0.0 V.