Two cells of emfs 1 V and 2 V and internal resistance 2 , and 1 , , respectively connected in parallel, gave a current of 1 A through an external resistance. If the polarity of one cell is reversed, then value of current through the external resistance will be 5 A. The value of is __________.

Step-by-step solution

For two cells connected in parallel with the same polarity, the equivalent emf E_ eq and equivalent internal resistance r_ eq are given by: E_ eq = E₁ r₂ + E₂ r₁ r₁ + r₂ r_ eq = r₁ r₂ r₁ + r₂ Substituting the given values ( E₁ = 1 V, r₁ = 2 , , E₂ = 2 V, r₂ = 1 , ): E_ eq = 1 1 + 2 2 2 + 1 = 5 3 V r_ eq = 2 1 2 + 1 = 2 3 , The current I through the external resistance R is 1 A: I = E_ eq R + r_ eq 1 = 5 3 R + 2 3 R + 2 3 = 5 3 R = 1 , When the polarity of one cell is reversed, the new equivalent emf E'_ eq becomes: