Question

A cell of e.m.f. 'E' is connected across a resistance 'R'. The potential difference across the terminals of the cell is 90% ofE. The internal resistance of the cell is ______.

Options

• 9R

• `"R"/9`

• `9/10`R

• `10/9`R

Answer 1

A cell of e.m.f. 'E' is connected across a resistance 'R'. The potential difference across the terminals of the cell is 90% of E. The internal resistance of the cell is `underline("R"/9)`.

Explanation:

r = `("E - V")/"V"`R

Now V = `9/10`E

`therefore "r" = (("E" - 9/10 "E")"R")/(9/10 "E")`

`= ("1E"/10 "R")/(9/10 "E") = "R"/9`