First slide
Motion of a charged particle
Question

An α particle is moving along a circle of radius  R with a constant angular velocity . Point  A lies in the same plane at a distance  2R from the centre. The point  A records magnetic field produced by α particle. If the minimum time interval between two successive times at which A records zero magnetic field is ‘t’, the angular speed  ω, in terms of  t is:

Moderate
Solution

‘A’ records zero magnetic field when  α particle is moving on a line which passes through  A, which happen when tangent to path passes through  A. Angle covered between two such point  B and C=2π3 as shown in figure.

Time taken to go from  B to  C is given as 

t=T3=2πω13

ω=2π3t

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