12th Class Physics Magnetism Question Bank Case Based (MCQs) - Moving Charges and Magnetism

  • question_answer
    Direction: Q.6 to Q.10
    A charged particle moving in a magnetic field experiences a force that is proportional to the strength of the magnetic field, the component of the velocity that is perpendicular to the magnetic field and the charge of the particle.
    This force is given by \[\overrightarrow{F}=q(\overrightarrow{v}\times \overrightarrow{B})\]where q is the electric charge of the particle, v is the instantaneous velocity of the particle, and B is the magnetic field (in Tesla).
    The direction of force is determined by the rules of cross product of two vectors.
    Force is perpendicular to both velocity and magnetic field.
    Its direction is same as \[\overrightarrow{v}\times \overrightarrow{B}\] if q is positive and opposite to \[\overrightarrow{v}\times \overrightarrow{B}\] if q is negative.
    The force is always perpendicular to both the velocity of the particle and the magnetic field that created it. Because the magnetic force is always perpendicular to the motion, the magnetic field can do no work on an isolated charge. It can only do work indirectly, via the electric field. generated by a changing magnetic field.
    Read the given passage carefully and give the answer of the following questions.
    When a magnetic field is applied on a stationary electron, it:

    A) remains stationary        

    B) spins about its own axis

    C) moves in the direction of the field                      

    D) moves perpendicular to the direction of the field.

    Correct Answer: A

    Solution :

    (a) remains stationary                                    For stationary electron, \[\overrightarrow{v}=0\] \[\therefore \] Force on the electron \[{{\overrightarrow{F}}_{m}}=-e(\overrightarrow{v}\times \overrightarrow{B})=0\]


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