WAEC Physics 2020 Objective — Question 28
Question 28 of 50 from the West African Examinations Council (WAEC) Physics 2020 Objective paper, with the correct answer and a full explanation.
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An electron of mass m and charge e moves in a circular path in a magnetic field of flux density B. How long does it take to complete one orbit?
- A. 2me/B(pi)
- B. 2B/me(pi)
- C. 2(pi)m/BeCorrect
- D. B e/2(pi)m
Explanation
The magnetic force on the charge provides the centripetal force for the circular path: F=evB=mv^2/r, so r=mv/(eB). The angular speed omega=v/r=eB/m. The time period T=2(pi)/omega=2(pi)m/(Be).
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