In a mass spectrometer, ions of the same charge and speed but different masses are separated because
Correct answer: B. heavier ions follow a path of larger radius in the magnetic field
- A. heavier ions move faster
- B. heavier ions follow a path of larger radius in the magnetic field
- C. lighter ions are stopped by the field
- D. heavier ions lose their charge
Explanation
The radius mv over qB is proportional to mass when charge, speed and field are fixed, so heavier ions curve less sharply and strike the detector further along. Measuring where each beam lands therefore measures the mass. This is how isotopes were discovered and how their relative abundances are determined.
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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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