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NEET-XII-Physics

04: Moving Charges And Magnetism

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  • #22
    The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?
    Ans : Current in both wires, I = 300 A

    Distance between the wires, r = 1.5 cm = 0.015 m

    Length of the two wires, l = 70 cm = 0.7 m

    Force between the two wires is given by the relation,



    Where,

    = Permeability of free space =



    Since the direction of the current in the wires is opposite, a repulsive force exists between them.