Question

(1)
If the length of a potentiometer wire is increased by keeping
constant potential difference across the wire, then

Answer 1

answer : option (a) null point is obtained at larger distance.

you should apply relation of potential gradient and length.

i.e., k = V/L , where V is potential difference , k is potential gradient and L is length of wire.

now if length of wire is increased, potential gradient will decrease. it means, null point is obtained at longer distance.

analytical method : Let voltage of driving source is V, cell voltage is E (initial potential) , L1 is initial length of wire and l is balancing length.

then, E/V = l/L1 .......(1)

case 2 : after changing the length of wire of potentiometer = L2, balancing length = l'

then, E/V = l'/L2......(2)

from equations (1) and (2),

l' = l(L2/L1)

as it is given, L2 > L1

so, l' > l

hence null point is obtained at larger distance.

[ some more points : sensitivity is inversely proportional to potential gradient. it means that smallest potential difference that can be measured with help of potentiometer. ]

Answer 2

$\huge\star\mathfrak\blue{{Answer:-}}$

if the length of potentiometer wire increased by keeping constant potential difference across the wire. Pravin, if the length of potentiometer wire is increased by keeping constant potential diff. ... As you know, the potential gradient is equal to V/L ie Potential difference divided by length of the wire