A resistor 'R' and 2µF capacitor in series is connected through a switch to 200 V direct supply. Across the capacitor is a neon bulb that lights up at 120 V. Calculate the value of R to make the bulb light up 5s after the switch has been closed. (log 10 2.5 = 0.4)
Text Solution
Verified by ExpertsThe correct answer is:
C
v = 200(1 – e – t/ τ )
120 = 200(1 – e – t/ τ )
e – t/ τ = 
= 
t/ τ = log(2.5) = 0.4
= (0.4) × R × 2 × 10 – 6
R = 
= R = 2.7 × 10 6
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