The potentiometer wire `AB` is `600` cm long.
a. At what distance from A should be jockey `J` touch the wire to get zero deflection i the galvanometer.
b. If the jockey touches the wire at a distance `560 cm` from A, what will be the current through the galvanometer.

Answer

(a)` 320 cm`(b)` (3E)/(8r)`

Explanation

Current through potentiometer wire
`I = (E )/(15 r + r) = (E )/(16 r)`
potential drop across potentiometer wire
`= (E )/(16 r) xx 15 r = (15E )/(16)`
potential gradient of potentiometer wire
`K = (15 E//16)/(600) "volt"//cm`
(a) UIf galvanometer shown zero deffiection at length `l` of potentiometer wire , then
`(E )/(2) = K1 = (15 E)/(16 xx 600)I`
`or l = (16 xx 600)/(15 xx 2) = 320 cm`
(b) Fall of potential across the length `560 cm = K xx 560` volt .If `l` is the current through galvanometer arm , then
`K xx 560 - (E )/(2) = I r or (15 E)/(16 xx 600) xx 560 - (E )/(2) = I r `
`or I = (3E)/(8r)`