WAEC Physics 2020 Objective — Question 33
Question 33 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. The magnetic force on the charge is given by
- A. F=evB sin90 = qvBCorrect
- B. F=evB cos90
- C. F=ev/B
- D. F=eB/v
Explanation
The magnetic force on the charge is given by F=evB sin90=qvB, the centripetal force (mv^2/r) needed for the circular path is provided by the magnetic force. Thus evB/r=mv/r and r=mv/(qB).
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