A piece of wire of resistance `R` is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is `R'`, then the ratio `R//R'` is :

Options

A. `1//25`
B. `1//5`
C. 5
D. 25

Answer

D

Explanation

All the five parts are connected in parallel. Hence, equivalent resistance (R.) is given
`(1)/(R )=(1)/(R//5)+(1)/(R//5)+(1)/(R//5)+(1)/(R//5)+(1)/(R//5)+(1)/(R//5)`
`rarr (1)/(R )=(5)/(R )+(5)/(R )+(5)/(R )+(5)/(R )+(5)/(R )+(5)/(R )+(5)/(R )=(25)/(R )`
`rarr (R)/(R.)=1/25`
so `(R )/(R.)=25`