Question

• Select and write correct answers of the following questions :
(1)
If the length of a potentiometer wire is increased by keeping
constant potential difference across the wire, then
(a) null point is obtained at larger distance
(b) there is no change in the null point
(c) potential gradient is increased
(d) null point is obtained at shorter distance​

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

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

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.