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A filament bulb (400W, 100V ) is to be u...

A filament bulb (400W, 100V ) is to be used in a 230V main supply . When a resistance R is conneted in series , the bulb work at rated voltage and consume 400W. The value of R is

A

`27.5Omega`

B

`32.5Omega`

C

`26Omega`

D

`35Omega`

Text Solution

Verified by Experts

The correct Answer is:
B
Use `P=V^2/R`

`R_("bulb")=V^2/P=(100xx100)/(400) = 25Omega`
`V_("bulb") = 100V`
`100-(R_("bulb"))/(R+R_("bulb"))xx230`
`100=(25)/(25+R)xx230`
`100+4R=230`
`R=130/4=32.5Omega`
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