Single Choice

Two particles each of mass $$m$$ and carrying charge $$Q$$ are separated by some distance. If they are in equilibrium under mutual gravitational and electrostatic forces, then Q/m (in C/Kg) is of the order of:

A$$10^{-5}$$
B$$10^{-10}$$
Correct Answer
C$$10^{-15}$$
D$$10^{-20}$$

Solution

Given : Gravitational force = Electrostatics force
Let the distance between the rwo charges be $$r$$.
$$\Rightarrow \dfrac{G(m)m}{r^2}= \dfrac{K\ Q\ . Q}{r^2}$$
$$\Rightarrow \dfrac{G}{K}= \dfrac{Q^2}{m^2}$$
$$\Rightarrow\sqrt{\dfrac{6.67\times 10^{-11}}{9\times 10^9}}= \dfrac{Q}{m}$$
$$\therefore \dfrac{Q}{m}$$ is the order of $$10^{-10}$$

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