Electrostatics 6 Question 3

3. A 4μF capacitor and a resistance of 2.5MΩ are in series with 12 V battery. Find the time after which the potential difference across the capacitor is 3 times the potential difference across the resistor. [Given, ln(2)=0.693 ]

(2005, 2M)

(a) 13.86 s

(b) 6.93 s

(c) 7 s

(d) 14 s

(1983,6M)

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Answer:

Correct Answer: 3. (a)

Solution:

  1. Given : VC=3VR=3(VVC)

Here, V is the applied potential.

VC=34V or V(1et/τc)=34Vet/τc=14

Here,

τc=CR=10 s

Substituting this value of τc in Eq. (i) and solving for t, we get

t=13.86 s

Correct answer is (a).



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