A) \[3.3\times {{10}^{7}}\Omega \]
B) \[1.3\times {{10}^{4}}\Omega \]
C) \[1.7\times {{10}^{5}}\Omega \]
D) \[2.7\times {{10}^{6}}\Omega \]
Correct Answer: D
Solution :
Charge on capacitor \[q={{q}_{0}}(1-{{e}^{-t/RC}})\] or \[V=\frac{{{q}_{0}}}{C}(1-{{e}^{-t/RC}})\] \[V=200(1-{{e}^{-t/RC}})\] \[120-200(1-{{e}^{-t/RC}})\] \[{{e}^{-t/RC}}=0.4\] \[\frac{-t}{RC}=\ln (0.4)\] \[\frac{t}{RC}=\ln \left( \frac{10}{4} \right)=2.303\times 0.4\] \[R=\frac{5}{2\times {{10}^{-6}}\times 2.303\times 0.4}\] \[=2.7\times {{10}^{6}}\Omega \]
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