Resistance in the two gaps of a meter bridge are `10 ohm` and `30 ohm` respectively. If the resistances are interchanged he balance point shifts by

Options

A. 33.3 cm
B. 66.67 cm
C. 25 cm
D. 50 cm

Answer

D

Explanation

First case, `(10)/(30)=(l)/((100-l))`
`therefore 3 l=100-l therefore 4l =100 therefore l= 25 cm`
Second case, `(30)/(10)=(l')/((100-l'))`
`therefore 3(100-l')=l' therefore 300-3l'=l'`
`therefore 4l' =300 therefore l'= 75 cm `
`therefore " Shift in the null point " =75-25=50 cm`