Two resistances prepared from the wire of the same material having diameters in the ratio 3:1 and length in the ratio 3:1 are connected in the left and right gap of Wheatstone's metre bridge.The distance of null point from the left end of the wire is

Options

A. 55 cm
B. 25 cm
C. 35 cm
D. 52 cm

Answer

B

Explanation

`(R_(1))/(R_(2))=(l_(x))/(l_(r))`
`:.(l_(1))/(l_(2))xx(pi r_(2)^(2))/(pi r_(1)^(2))=(l_(x))/(100-l_(x))`
`:.l_(x)=25cm`