Consider the potentiometer circuit arranged as in figure. The potentiometer wire is 600cm long. At what distance from the point A should the jockey touch the wire to get zero deflection in the galvanometer? b) If the jockey touches the wire at a distance of 560cm from A, What will be the current in the galvanometer?

Explanation

Resistance per unit length = 15r/6
For length x, rx = 15rx/6
For the loop PASQ
` (i_1 +i_1) 15/6 rx + 15/6 r(6-x) i_1 + i_1 r = epsilon ………….(i) `
for the loop awtm,
` i_2r - 15/6 rx (i_1 + i_1) = epsilon /2 `
` rArr i_2 + 15/6 rx (i_1 + i_1) = epsilon /2 ...........(ii) `
For zero deflection in galvanometer, `i_2 =0` .
` 15/6 rx. i_1 = epsilon /2 `
` rArr i_1 = epsilon/5.r `
` Putting i_1 = epsilon/5.r `
` and i_2 = 0 in eqn. (i) `
` we get, x = 320 cm. `
`(b) Putting x = 5.6 and solving equation`
` (i) & (ii) `
` we get, i_2 = 2epsilon/ 22r ` .