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Motion Of Charged Particle in Magnetic Field

Particle Motion under O Magntic Field:

(Secondary Information)

= q (




If charge is projected

to the Magnetic Field. The path of the charged particle is purely circular and magnetic force povides necessary centripedal force.

R = Radius of the path.


T = Time period of the path.


Otherwise particle moves in a helical path:


Radius =


Time Period =


Pitch = V11x T =



is velocity

to magnetic field V11

is velocity 11 to the magnetic field.

Force on a current carrying wire



(Secondary Information)


As F = q(





We can say,

= dq(







   dF = I( x )

Torque on a Current Carrying Loop



Net force on a closed loop is always zero. But there is always a net torque acting on the loop.


Given by

= Magnetic Moment

= Magnetic Field.

Secondary Information



Let plane of the loop is inclined at an angle 10 -

to magnetic field (

with normal to the plane).



Trque = Bil(sin




        = B[l(lb)]sin

        = [µ x B]




dV =


    = µB(cos


- cos




   U = - .B

Dumb Question



Q1. A rectangular current loop is in an arbitrary orientation is an external magnetic field. Is any work required to rotate the loop about an axis perpendicular to its plane ?


Ans: No, no work is required.


Q2. two wires are II to each other in an external magnetic field with their in same direction. Will they attract or repet ?


Ans: They will attract each other.


Q3. A particle enters a external magnetic field

to it like shown in figure.



In which direction relative to initial air.... will .. leave the field.


Ans: It will complete half circle and leave II to initial direction.


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