Two cells of e.m.f. 10V & 15V are connected in parallel to each other between points A&B. The cell of e.m.f. 10V is ideal but the cell of e.m.f. 15V has internal resistance `1Omega`. The equivalent e.m.f. between A and B is:

Options

A. 25/2 V
B. not defined
C. 15 V
D. 10 V

Answer

D

Explanation

For ideal ` r to 0`
`E=(10/r+15/1)/(1/r+1/1)=(10+15r)/(1+r)`
`E=10 V`