Five cells each of emf E and internal resistance r send the same amount of current through an external resistance R whether the cells are connected in parallel or in series. Then, the ratio`((R)/(r))` is

Options

A. 2
B. `1/2`
C. `1/5`
D. 1

Answer

D

Explanation

When 5 cell are joined in parallel as shown.

`i=(5E)/(5R +r)" "...(i)`
When 5 cell are joined in series as shown.

`i=(5E)/(5r + R)" "...(ii)`
So, according to the questions
`(5E)/(5R + r ) = ( 5E)/(5 r + R)`
`5 R + r = 5 r + R`
`4R = 4r implies (R)/(r)= (4)/(4)`
`(R )/(r)=1`