J J Science Academy - Electrostatics Test

Question 1: Three charges, $(+q)$ $(+q)$ $(-q)$, are placed at the three corners of an equilateral triangle, of side $(L)$. The potential energy of the system is

1) V=0, E = 0 2) $(V=0, E \neq 0)$ 3) $(V \neq 0, E=0)$ 4) $(V \neq 0, E \neq 0)$

Question 2: Two similar charged small spheres, each having a charge Q are suspended from a point by a thread of length L . At equilibrium, the angle made by the threads with the vertical is $(30^{\circ})$. The electrostatic PE of the system at equilibrium, is

1) $(\frac{kQ^{2}}{L})$ 2) $(\frac{\sqrt{3} kQ^{2}}{2 L})$ 3) $(\frac{kQ^{2}}{\sqrt{3} L})$ 4) $(\frac{\sqrt{3} kQ^{2}}{L})$

Question 3: P.E. of system of charges, shown in the figure, is

1) $(\frac{3}{4 \pi \varepsilon_{0}} \frac{q^{2}}{r})$ 2) $(\frac{1}{4 \pi \varepsilon_{0}} \frac{q^{2}}{r})$ 3) $(-\frac{1}{4 \pi \varepsilon_{0}} \frac{q^{2}}{r})$ 4) $(-\frac{3}{4 \pi \varepsilon_{0}} \frac{q^{2}}{r})$

Question 4: The value of Q , for which the PE of system is zero, is

1) $(-\frac{q}{\sqrt{2}})$ 2) $(-0.47 q)$ 3) $(-\sqrt{2} q)$ 4) $(\frac{q}{\sqrt{2}})$

Question 5: Three positive charges are placed at the vertices of an equilateral triangle. A negative charge is placed at the centre of the triangle. The P.E of the system will

1) Increase

Question 6: Three charges $(1 \times 10^{-8} C)$, $(2 \times 10^{-8} C)$ and $(3 \times 10^{-8} C)$ are placed at $(x=1 cm)$, $(x=2 cm)$, and $(x=3 cm)$, respectively, on x -axis from the origin. The potential energy of this arrangement relative to the potential energy for infinite separation is

1) $(7.9 \times10-2 J)$ 2) $(8.55 \times 10^{-4} J)$ 3) $(6.5 \times 10^{-7} J)$