# Question: aconsider the case of a point test charge q moving...

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a)Consider the case of a point test charge q moving with velocity u parallel to an infinitely long straight current. Let λ be the proper charge density of the positive ions and v be the drift velocity of the electrons in the wire. Calculate the charge density of the wire relative to the rest-frame of the test charge q. b) Prove that the force ˜f the test charge feels in its rest-frame corresponds exactly to the force f on it in the rest-frame of the wire, when force transformation formulas are employed.