A cell in the secondary circuit gives null deflection for 2.5 m length of a potentiometer having 10m length of wire. If the length of the potentiometer wire is increased by 1m without changing the cell in the primary, the position of the null point wil be

Options

A. 3.5 m
B. 3 m
C. 2.75 m
D. 2.0 m

Answer

C

Explanation

In the first case, potential gradient `=(V)/(L)=(V)/(10)=K`
In the second case, `K'=(V)/(11)` since l is increased by 1m.
`therefore K' lt K therefore` The balancing length will increase.
In the first case, `V= K l_(1)`
In the second case, `V= K'l_(2)`
`therefore Kl_(1)=K'l_(2)`
`therefore l_(2)=(Kl_(1))/(K')=(V)/(10)xx2.5xx(11)/(V)`
`=2.5xx(11)/(10)=2.75 m`
`therefore` The null point will be at 2.75 m.