A particle passes through a mass spectrometer as illustrated in the figure below
ID: 1391059 • Letter: A
Question
A particle passes through a mass spectrometer as illustrated in the figure below. The electric field between the plates of the velocity selector has a magnitude of 8285 V/m, and the magnetic fields in both the velocity selector and the deflection chamber have magnitudes of 0.0933 T. In the deflection chamber the particle strikes a photographic plate 55.5 cm removed from its exit point after traveling in a semicircle.
(a) What is the mass-to-charge ratio of the particle?
(b) What is the mass of the particle if it is doubly ionized?
(c) What is its identity, assuming it's an element?
Explanation / Answer
(a)
The radius of motion = 55.5cm/2 = 27.5 cm = 0.0.275m
For the velocity selector, the electric force balances the magentic force so the particle moves in a straight line:
qE = Bqv
v = E/B = 8285/0.0933 = 88800m/s
For the circular motion, the centripetal force is provided by the magnetic force:
mv
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