Question

Five identical cells each of internal resistance 1Ω and emf 5V are connected in series and in parallel with an external resistance 'R'. For what value of 'R', current in series and parallel combination will remain the same?

Options

• 1 Ω

• 25 Ω

• 5 Ω

• 10 Ω

Answer 1

1 Ω

Explanation:

i_r = `25/(5+"R")`

in parallel, E_eq = E = 5V

r_eq = `"r"/5=1/5`Ω

i₂ = `5/("R"+1/5)`

putting i₁ = i₂,

we get, 4R = 4 ⇒ R = 1Ω.