1.

Simple replace the resistor with capacitors and ohms to micro farad and calculate total capacitance

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A resistor R and 2 μF 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. Find the value of R to make the bulb light up 5 s after the switch has been closed. (log

10

2.5=0.4)

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Answer

Correct option is

C

2.7×10

6

Ω

V

c

=200(1−e

−t/τ

)

120=200(1−e

−t/τ

)

e

−t/τ

=

200

200−120

=

200

80

+

τ

t

=log

e

(2.5)=

0.43

0.4

=0.92

τ=RC

⇒R=

0.92×2×10

−6

5

⇒R=2.71×10

6

Ω



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