Find the effective resistance of the combination of two resistors of resistances 10 Ω and 15 Ω connected in (i) Series (ii) Parallel.

Solution: Data: R₁ = 10 Ω , R₂ = 15Ω , R_s = ?, R_p = ?

(i) R_s = R₁ + R₂ = 10 Ω + 15Ω = 25Ω

The effective resistance in the series combination = 25 Ω

(ii) 1/R_p = 1/R₁ + 1/R₂ = 1/10Ω +1/15Ω = 5/30Ω

∴ R_p = 30Ω/5 = 6Ω

The effective resistance in the parallel combination = 6 Ω.