Question

Figure shows a long potentiometer wire AB having a constant potential gradient. The null points for the two primary cells of emfs ε₁ and ε₂ connected in the manner shown are obtained at a distance of l₁ =120 cm and l₂ =300 cm from the end A. Determine (i) ε₁/ε₂ and (ii) position of null point for the cell ε₁ only.

Answer 1

Let k = potential gradient in V/cm

ε₁ +ε₂ = 300k ...(i)

ε₁ +ε₂ = 120k ...(ii)

Adding (i) and (ii), we get 2ε₁= 420k

ε₁ =210k

Substituting the value of ε₁ in equation (i), we get ε₂ =90k

Therefore,ε_1/ε₂ = 210/90 = 7/4

Balancing length for cell ε₁ is 210 cm