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Question
Calculate the current through a 60 W lamp rated for 250 V. If the line voltage falls to 200 V, how is the power consumed by the bulb affected?
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Solution
Given,
Power (P) = 60 W
Voltage (V) = 250 V
We know that,
Power (P) = VI
Substituting the values in the formula above, we get,
`60 = 250 xx "I"`
`=> "I" = 60/250`
`=> "I" = 0.24 A`
Hence, current through the lamp = 0.24 A
Power consumed when voltage is 200 V = ?
Resistance of lamp (R) = `"V"^2/"P"`
Substituting the values in the formula, we get,
R = `250^2/60`
⇒ R = 1041.6 Ω
From relation,
P = `"V"^2/"R"`
Substituting the values in the formula, we get,
P = `200^2/1041.6`
⇒ P = 38.4 W
Hence, power consumed reduces to 38.4 W.
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