A particle passes through a mass spectrometer as illustrated in the figure below

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 8446 V/m, and the magnetic fields in both the velocity selector and the deflection chamber have magnitudes of 0.0942 T. In the deflection chamber the particle strikes a photographic plate 11.9 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 two forces on the object must be equal for the molecule to enter the deflection chamer. qE = qvB E = vB v = E/B So, v=(8446V/m)/(.0942 T)=795.61 m/s. In the deflection chamber, only ions traveling at 83,116 m/s enter, and with a charge of +1 eV. The magnetic force is also the centripetal force. F = qvBo = mv^2/r Get r by itself for the radius. r = mv/qBo (0.119/2)=(m/q)*795.61/0.0942----------> m/q=7*10^-7kg/C b) mass of the particle if it is doubly ionized=2X1.6X10^-19X7X10^-7=2.2543X10^-24kg

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