When an electron moving with a uniform speed in a vacuum enters a magnetic field in a direction perpendicular to the field the subsequent path of the electron is ___________________?
Correct answer: C. a circle in a plane perpendicular to the field
- A. a straight line parallel to the field
- B. a parabola in a plane perpendicular to the field
- C. a circle in a plane perpendicular to the field
- D. a straight line along its initial direction
Explanation
For velocity perpendicular to the magnetic field, the magnetic force qvB is always perpendicular to the velocity and acts as centripetal force, so the electron follows a circle in a plane perpendicular to the field. The likely wrong choice is d, which would occur if the magnetic force were zero or the velocity were parallel to the field.
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About Charged Particle in a Magnetic Field
A charged particle moving through a magnetic field experiences the Lorentz force, which is perpendicular to both its velocity and the field. The motion may be circular or helical, with questions involving radius, angular frequency, time period, and work done. A stationary charge feels no magnetic force.
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