Question 131: Electrostats & Capacitance

Question

Two point charges A = +3 nC and B = +1 nC are placed 5 cm apart in air. The work done to move charge B towards A by 1 cm is

Accepted Answer

The given situation is shown below
$$\begin{aligned}
r_1 & =1 \mathrm{~cm} \
& =1 	imes 10^{-2} \mathrm{~m} \
r_2 & =5-1 \
& =4 \mathrm{~cm} \
& =4 	imes 10^{-2} \mathrm{~m}
\end{aligned}$$
$$\begin{aligned}
	ext { Required work done } & =	ext { Changes in potential energy } \
& =k q_A q_B\left[\frac{1}{r_2}-\frac{1}{r_1}ight] \
& =9 	imes 10^9 	imes 3 	imes 10^{-9} 	imes 10^{-9} \
& {\left[\frac{1}{4 	imes 10^{-2}}-\frac{1}{1 	imes 10^{-2}}ight] } \
& =1.35 	imes 10^{-7} \mathrm{~J}
\end{aligned}$$

Answer

$$2.0	imes10^{-7}$$ J

Answer

$$1.35	imes10^{-7}$$ J

Answer

$$2.7	imes10^{-7}$$ J

Answer

$$12.1	imes10^{-7}$$ J

Electrostats & Capacitance

Two point charges A = +3 nC and B = +1 nC are placed 5 cm apart in air. The work done to move charge B towards A by 1 cm is

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