Vi=4πϵ01[(0.4)q1q3+(0.3)q1q2+(0.5)q2q3]vf=4πϵ01[(0.4)q1q3+(0.3)q1q2+(0.1)q2q3] 
⇒ΔV=Vf−V1=4πϵ01q2q3(0.11−0.51)=πϵ0q2q3(10−2)=4πϵ0q3(8q2)⇒k=8q2
NEET UG 2005 — Physics Electromagnetism
2005mcqhard
Two charge q1 and q2 are placed 30 cm apart, as shown in the figure. A third charge q3 is moved along the are of a circle of radius 40 cm from C to D. The change in the potential energy of the system is 4π∈0q3k, where k is: 
Official previous-year question
Held on 30 Apr 2005 · Verified 9 Jul 2026.
Options
- A
8q1
- B
6q1
- C
8q2
- D
6q2
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