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Three identical charges q₁, q₂ and q₃ are placed, in that order, on three consecutive vertices of a square. If the force acting between q₁ and q₂ is F₁₂ and that between q₁ and q₃ is F₁₃, then (F₁₃)/(F₁₂)=

Asked in GUJCET 2018 · Coulomb's law and superposition

• (1) 1/2
• (2) 2
• (3) 1/(√2)
• (4) √2

Step-by-step solution

Why the other options are wrong

• (2) Upside down: q₃ sits across the diagonal, farther from q₁ than q₂ is, so F₁₃ must be the smaller force.
• (3) This is the ratio of the distances, a/(a√2), not of the forces. Coulomb's law squares the distance.
• (4) Distances again instead of forces, and inverted as well. The force ratio goes as the square of the distance ratio.

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