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A resistor 'R' and 2(mu)F capacitor in s...

A resistor 'R' and `2(mu)F` capacitor in series is connected through a switch to 200 V direct supply. A cross the capacitor is a neon bulb that lights up at 120 V. Calculate the value of R to make the bulb light up 5 s after the switch has been closed. (`log_(10) 2.5 = 0.4`)

A

`1.3xx10^(4)Omega`

B

`1.7xx10^(5)Omega`

C

`2.7xx10^(6)Omega`

D

`3.3xx10^(7)Omega`

Text Solution

Verified by Experts

The correct Answer is:
C
For charging of capacitor
`V=V_(0)(1-e^(-t//RC))`
`implies120=200(1-e^(-t//RC))`
`implies1-e^(-t//RC)=(3)/(5)impliese^(-t//RC)=(2)/(5)`
`implies (t)/(RC)=l n((5)/(2))=2.303log(2.5)`
`impliesR=(t)/(Cxx2.303log(2.5))=(5)/(2xx10^(-6)xx2.303xx0.4)`
`=2.7xx10^(6)Omega`.
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