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We have a 30 W, 6 V bulb , which we want...

We have a `30 W, 6 V` bulb , which we want to glow by a supply of `120 V` . What can be done for this ?

Text Solution

Verified by Experts

Here, P = 30 W, V = 6 V
`:.` Resistance of the bulb,
`R = (V^(2))/P = ((6)^(2))/30 = 1.2 Omega`
Current capacity of the bulb, `I = P/V = 30/6 = 5A`
Supply voltage, `V' = 120 V`
Let R' be the resistance used in series with the bulb to have a current of 5 A in the circuit.
Total resistance = `R' + R = (R' + 1.2)`
`:.` Current, `I = V'//(R' + 1.2)`
or ` 5 = 120/R'+1.2`
or `R' = 120/5 - 1.2 = 22.8 Omega` in series
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