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Electrostatics question

2013 · Q133
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Electrostatics question

2013 · Q133

NEETPhysicsElectrostaticsMCQ+4 / −1
Two pith balls carrying equal charges are suspended from a common point by strings of equal length, the equilibrium separation between them is r. Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become

NEET 2013 Physics - Electrostatics Question 62 English
  1. A
    (2r3)\left( {{{2r} \over {\sqrt 3 }}} \right)(3​2r​)
  2. B
    (2r3)\left( {{{2r} \over 3}} \right)(32r​)
  3. C
    (12)2{\left( {{1 \over {\sqrt 2 }}} \right)^2}(2​1​)2
  4. D
    (r23)\left( {{r \over {\sqrt[3]2 }}} \right)(32​r​)
View written solutionFree

Correct answer: D

NEET 2013 Physics - Electrostatics Question 62 English Explanation
From figure,
$$\tan \theta = {{{F_e}} \over {mg}} \Rightarrow {{r/2} \over y} = {{{{k{q^2}} \over {{r^2}}}} \over {mg}}$$
   $$\left[\because {F = {{k{q^2}} \over {{r^2}}}} { from \,coulomb’s \,law} \right]$$

$$ \Rightarrow {r^3} \propto y \Rightarrow r{'^3} \propto {y \over 2} \Rightarrow {{r'} \over r} = {1 \over {{2^{1/3}}}}$$

$$ \Rightarrow r' = {r \over {\sqrt[3]2 }}$$
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