Electrostatics Question 252

Question: A metallic shell has a point charge -q? kept inside its cavity. Which one of the following diagrams correctly represents the electric lines of forces [IIT-JEE (Screening) 2003]

Options:

A) x

B) x2

C) x3

D) 1/x

Show Answer

Answer:

Correct Answer: B

Solution:

Initially (i) potential energy of Q is Ui=2kqQa ……(i) (ii)

when charge Q is displaced by small distance x then it’s potential energy now Uf=kqQ[1(a+x)+1(ax)]

=2kqQa(a2x2) …….(ii)

Hence change in potential energy ΔU=UfUi=2kqQ[aa2x21a]

=2kqQx2(a2x2)

Since x « a so ΔU=2kqQx2a2ΔUx2



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