Two electric bulbs A and B are marked 220 V, 40 W and 220 V, 60 W respectively. Which one of these bulbs has higher resistance?
Given, two electrical bulbs.
Potential across first bulb, V1= 220 V
Power of first bulb, P1= 40 W
Potential across second bulb, V2 = 220 V
Power of second bulb, P2 = 60 WNow,
P = V
2/R or R = V2/P i.e., R ∝ 1/P.Resistance is inversely proportional to power.
Therefore, the first bulb having lesser power has higher resistance.
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If two electric bulbs have 40 W and 60 W ratings at 220 V, then the ratio of their resistances will be
Options
(a) (3:2) (b) (2:3) (c) (3:4)
(d) (4:3)
Correct Answer:
(3:2)
Explanation:
P = V² / R
⇒ R₁ / R₂ = P₂ / P₁ = 60 / 40 = 3 / 2 = 3 : 2