Q149 / 160 · AP EAMCET 2021 (25 Aug Shift 1) · Physics

Two insulated charged metallic spheres $P$ and $Q$ of negligible radii have their centres separated by a distance of $60 \mathrm{~cm}$. The mutual force of electrostatic repulsion, if the charge on each is $6 \times 10^{-7} \mathrm{C}$ is

  • Correct answer
    A
    $9 \times 10^{-3} \mathrm{~N}$
  • B
    $2.5 \times 10^{-9} \mathrm{~N}$
  • C
    $5.2 \times 10^{-4} \mathrm{~N}$
  • D
    $9 \times 10^{-9} \mathrm{~N}$

Solution

Given, $$ Q=6 \times 10^{-7} \mathrm{C} $$ $$ d=60 \mathrm{~cm}=0.6 \mathrm{~m} $$ Force, $$ \begin{aligned} F=\frac{k Q^2}{d^2} & =\frac{1}{4 \pi \varepsilon_0} \frac{\left(6 \times 10^{-7}\right)}{(0.6)^2} \\ & =9 \times 10^9 \times 10^{-14} \times 10^2 \\ & =9 \times 10^{-3} \mathrm{~N} \end{aligned} $$

Hence, the correct answer is option: 'A'.

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