The principle of a simple form of mass spectrometer ions is to pass through narrow slits S1 and S2 and into a velocity selector. The ions after passing through the slit S3 are deviated by a uniform magnetic field. The quantities that must remain constant for all ions arriving at the photographic plate are:
Correct answer: B. Charge/mass(e/m)
- A. Charged
- B. Charge/mass(e/m)
- C. Kinetic energy
- D. Mass
Explanation
The formula used in mass spectrometry is q/m = v/Br where q is the charge, m is mass, v is velocity, B is magnetic field strength, and r is the radius. The ions are arriving at the same point, so they have the same radius. v and B are equal as the same spectrometer is used. So for the equation to be the same for all ions, q/m must also be the constant for all ions.
This question appeared on the ETEA MDCAT 2015 paper, which you can sit online with every answer explained.
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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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