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A resistor R and a 4muF capacitor are connected in series across a 200 V d.c. supply. Across the capacitor is connected a neon lamp that strikes at 120 V in 5 seconds . Find R. |
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Answer» SOLUTION :`V= V_0 (1- e^(-t//tau_c))` where `tau_C= RC` or `120 = 200 (1- e^(-5//tau_C))` or , `(e^(-5//tau_C))= 1 -(120)/(200) =0.4` or, `(e^(5//tau_C) =log_e 2.5` or , `(5//tau_C)= log_(e) 2.5` `therefore tau_C = 5/(log_e 2.5) = 5.46 ` sec or, RC= 5.46 or, `R= (5.46)/(C) = (5.46)/(C) = (5.46)/(4XX10^(-6)) = 1.364 xx 10^6 `ohm = `1.364 M Omega` |
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