1. Concept: If a charge is positioned perfectly midway between two identical source charges, the electric fields from the two sources cancel each other out completely.
2. Formula: $$ \sum \vec{F} = \vec{F_{left}} + \vec{F_{right}} = 0 $$
3. Solution: - The source charge on the left pushes/pulls \( Q \) with force magnitude \( k(q)(Q)/r^2 \).
- The source charge on the right pushes/pulls \( Q \) with the exact same magnitude \( k(q)(Q)/r^2 \), but in the perfectly opposite spatial direction.
- By the definition of equilibrium, the sum of all forces is completely zero.
- , the official answer key specifies C as the expected response.*
4. Why other options are incorrect: Options B and D imply an unbalanced residual force, which physically violates symmetry.
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