If both the resistance and the inductance in an LR AC series circuit are doubled

If both the resistance and the inductance in an LR AC series circuit are doubled the new impedance will be

(a) halved
(b) fourfold
(c) doubled
(d) quadrupled

doubled

For L-R circuit, Z = √(R² + Xʟ²)

Z₁ = √(R₁² + Xʟ₂²)

Z₂ = √(R₂² + Xʟ₂²)

Given, R₂ = 2R and Xʟ₂ = 2Xʟ

Then, Z₂ = √[(2R)² + (2Xʟ)²] = 2 Z₁

KL2013

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