Question

If the power dissipated in 5Ω is 20 W then power dissipated in 4Ω is -

(1) 4 W 

(2) 6 W

(3) 10 W 

(4) 20 W

Answer 1

Correct Answer is: (1) 4 W 

P = VI = V² /R, voltage constant

P ∝ 1/R

then power in 10Ω will be 10W when I constant then

P = I² R

P ∝ R

P'/10 = 4/10 ⇒ P′ = 4W