In the vicinity of point charge, we place a 0.2μC charge so that a force of 5×10^−5 applied on it due to the charge q. Find the electric field produced by this unknown charge?

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.

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