A copper ball of density 8.0 g/cc and 1 cm in diameter is immersed in oil of density 0.8 g/cc. The charge on the ball if it remains just suspended in oil in an electric field of intensity 600π V/m acting in the upward direction is ________.

Fill in the blank with the correct answer from the options given below. (Take g = 10 m/s²)

$2 \times 10^{-5} C$

For equilibrium net force must be zero.

Volume is $ V = \frac{4\pi}{3} r^3 = \frac{4\pi}{3} 
(0.5\times 10^{-2})^3 = \frac{4\pi}{3} \times 125\times 10^{-9} m^3 = \frac{5\pi}{3} cc$

$ 8\times \frac{5\pi}{3}g = 0.8 \frac{5\pi}{3} g + q \times 600\pi$

$ 12 \pi g = 600\pi q \Rightarrow q = 2g \times 10^{-6} = 2\times 10^{-5}C$

The correct answer is Option (2) → $2 \times 10^{-5} C$