Two charges q₁ and q₂ are placed 30 cm apart as shown in the figure. A third charge q₃ is moved along an arc of a circle of radius 40 cm from C to D. Change in potential energy of the system is 4q₁q₃/(4πε₀k) where k is: [Diagram: Image]
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Question

Two charges q₁ and q₂ are placed 30 cm apart as shown in the figure. A third charge q₃ is moved along an arc of a circle of radius 40 cm from C to D. Change in potential energy of the system is 4q₁q₃/(4πε₀k) where k is: [Diagram: Image]

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G1 Physics · Accepted Answer

Step 1: Potential-energy change on moving q₃ is ΔU = q₃(Vᴅ − V𝒸). Step 2: Charge q₂ makes no contribution because its separation is the same at C and D. Step 3: Use the triangle distances 0.4, 0.3 and 0.5 m for q₁; source simplification yields the denominator constant requested in terms of q₁.