Electrostatics 5 Question 24

26. A parallel plate capacitor C with plates of unit area and separation d is filled with a liquid of dielectric constant K=2. The level of liquid is d/3 initially. Suppose the liquid level decreases at a constant speed v, the time constant as a function of time t is

(2008,3M)

(a) 6ε0R5d+3vt

(b) (15d+9vt)ε0R2d23dvt9v2t2

(c) 6ε0R5d3vt

(d) (15d9vt)ε0R2d2+3dvt9v2t2

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Answer:

Correct Answer: 26. (a)

Solution:

  1. After time t, thickeness of liquid will remain d3vt.

Now, time constant as function of time

τc=CR=ε0(1)R(dd3+vt)+d/3vt2

 Applying C=ε0Adt+tk

=6ε0R5d+3vt

Correct option is (a).



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