Question

Two charges q₁ and q₂ are placed 30 cm apart, as shown in the figure. A third charge q₃ is moved along the arc of a circle of radius 40 cm from C to D. The change in the potential energy of the system is\(\bigg(\frac{q_3}{4\pi\in_0}\bigg)k\),where k is:

• A. 8q₂
• B. 8q₁
• C. 4q₂
• D. 4q₁

Answer 1

The Correct Option is A

u₁ =14\(\pi\in_0\)[q₁q₂ 30×10−2+q₁q₂ 40×10^-2+q₂q₃ 50×10^-2 ]
u₂ =14\(\pi\in_0\)[q₁q₂ 30×10−2+q₁q₃ 40×10^-2+q₂q₃10×10^-2 ]
Δ_u= u₂−u₁=q₂q₃4\(\pi\in_0\)×102[110−150]
=q₂q₃4\(\pi\in_0\)×450×100
=q₃4\(\pi\in_0\)(8q₂)
∴k=8q₂

Therefore, the correct option is (A): 8q₂