At one instant an electron is moving in the positive x direction in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, its subsequent motion is:
Correct answer: B. Clockwise around a circle in the xy plane
- A. Straight ahead
- B. Clockwise around a circle in the xy plane
- C. Counterclockwise around a circle in the xy plane
- D. In the positive z direction
Explanation
The force on the electron (negative charge) is F = q(v × B). With v in +x and B in +z, the direction of v × B is -y. Since the charge is negative, the force is in the +y direction. This initial force pulls the electron into a circular path that is clockwise when viewed from the positive z-axis.
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About Electromagnetism
Magnetic flux density and magnetic flux describe the strength of a magnetic field and the field passing through a surface. A charged particle moving through a magnetic field experiences a force perpendicular to its velocity and may follow circular or helical motion, depending on the angle between velocity and field.
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