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NEET-XII-Physics

01: Electric Charges And Fields

I - page 4
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  • #27
    In a certain region of space, electric field is along the z-direction throughout. The magnitude of electric field is, however, not constant but increases uniformly along the positive z-direction, at the rate of 105 NC-1 per metre. What are the force and torque experienced by a system having a total dipole moment equal to 10-7 Cm in the negative z-direction?
    Ans : Dipole moment of the system, p = q × dl = -10-7 C m

    Rate of increase of electric field per unit length,



    Force (F) experienced by the system is given by the relation,

    F = qE





    = -10-7 × 10-5

    = -10-2 N

    The force is -10-2 N in the negative z-direction i.e., opposite to the direction of electric field. Hence, the angle between electric field and dipole moment is 180°.

    Torque (Ï„) is given by the relation,

    τ = pE sin180°

    = 0

    Therefore, the torque experienced by the system is zero.