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A charged particle of mass m and charge q travels on a circular path of radius r that is perpendicular to a magnetic field B. The time taken by the particle to complete one revolution is

Asked in JEE Main 2005 · Circular motion: radius, period and energy

• (1) (2π qB)/m
• (2) (2π m)/(qB)
• (3) (2π mq)/B
• (4) (2π mq)/(qB)

Step-by-step solution

Why the other options are wrong

• (1) Writes the angular frequency form upside down.
• (3) Puts the charge in the numerator.
• (4) Keeps a spurious q in the numerator, which cancels the charge dependence to give (2π m)/B.

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