Question 770: Electrostats & Capacitance

Question

Two point charges $+10 \mu \mathrm{C}$ and $4 \mu \mathrm{C}$ are placed 10 cm apart in air. The work required to be done to bring them 2 cm closer is
$$ \left(\frac{1}{4 \pi \varepsilon_0}=9 	imes 10^9 	ext { SI units }ight) $$

Accepted Answer

$$ \begin{aligned} & W=k \frac{q_1 q_2}{r_2}-k \frac{q_1 q_2}{r_1} \ & =9 	imes 10^9 	imes\left(4 	imes 10^{-6}ight) 	imes\left(10 	imes 10^{-6}ight)\left(\frac{1}{0.08}-\frac{1}{0.1}ight) \ & =360 	imes 2.5 	imes 10^{-3} \ & =900 	imes 10^{-3}=0.9 \mathrm{~J} \end{aligned} $$

Answer

0.65 J

Answer

0.9 J

Answer

1.2 J

Answer

2.3 J

Electrostats & Capacitance

Two point charges +10 \mu \mathrm{C} and 4 \mu \mathrm{C} are placed 10 cm apart in air. The work required to be done to bring them 2 cm closer is $ \left(\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9 \text { SI units }\right)

Choose the correct answer: