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JEE Advanced 2008Paper 2

Exam: JEE Advanced
Year: 2008
Paper: Paper 2
Subject: Physics
Chapter: Electrostatics

JEE Advanced 2008 · Paper 2 · Physics · Electrostatics

Consider a system of three charges (q)/(3), (q)/(3) and -(2 q)/(3)...

Consider a system of three charges

\frac{q}{3}, \frac{q}{3}

and

-\frac{2 q}{3}

placed at points

A, B

and

C

, respectively, as shown in the figure. Take

O

to be the centre of the circle of radius

R

and angle

C A B=60^{\circ}

.

Consider a system of three charges (q)/(3), (q)/(3) and -(2 q)/(3) placed at points A, B and C , respectively, as shown

Options

AThe electric field at point $O$ is $\frac{q}{8 \pi \varepsilon_0 R^2}$ directed along the negative $x$ -axis
BThe potential energy of the system is zero
CThe magnitude of the force between the charges at $C$ and $B$ is $\frac{q^2}{54 \pi \varepsilon_0 R^2}$
DThe potential at point $O$ is $\frac{q}{12 \pi \varepsilon_0 R}$

Correct answer

C. The magnitude of the force between the charges at $C$ and $B$ is $\frac{q^2}{54 \pi \varepsilon_0 R^2}$

Step-by-step solution

Distance

B C=A B \sin 60^{\circ}=(2 R) \frac{\sqrt{3}}{2}=\sqrt{3} R

\therefore \quad\left|F_{B C}\right|=\frac{1}{4 \pi \varepsilon_0} \frac{(q / 3)(2 q / 3)}{(\sqrt{3} R)^2}=\frac{q^2}{54 \pi \varepsilon_0 R^2}

\therefore

correct option is (c).

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