A circular loop of copper wire is placed next to a long, straight wire. The current I in the long, straight wire is increasing. What current does this induce in the circular loop?

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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.