Mass Spectrometer Part A J. J. Thomson is best known for his discoveries about t

Question

Mass Spectrometer Part A J. J. Thomson is best known for his discoveries about the nature of cathode rays. His other important contribution was the invention, together with one of his students, of the mass spectrometer, a device that measures the ratio of mass m to positive charge 4 of an ion. After being accelerated to a speed of 1.8510 m/s, the particle enters a uniform magnetic field of strength 0.800 T and travels in a circle of radius 350 m (determined by observing where it hits the screen as shown in the figure). The results of this experiment allow one to find m/q. Find the ratio m/q for this partide. Express your answer numerically in kilograms per coulomb. Hints The spectrometer consists of two regions as shown in the figure. Egure 1) In the first region an electric field accelerates the ion and in the second the ion follows a circular arc in a magnetic field. The radius of curvature of the arc can be measured and then the m/q ratio can be found. DVD AEg n r o . m/q kg/c Submit My Answers Give Up Incorrect; Try Again; 4 attempts remaining Provide Feedbach Continue Figure 1 of 1 . . . . . Rs. . . . . . . . .

Explanation / Answer

Let m = mass of particle, q = charge, v = speed, B = magentic field strength, r = radisu of curvature.
The particle is subject to force due to the magnetic field:
F = qvB
Which is balanced by a centripital force
Fc = mv^2/r
So equating the two:
F = Fc ---> qvB = mv^2/r ---> re-arrange to get m/q
m/q = rB/v = 0.35m* 0.8T/1.85x10^5 m/s = 1.514x10^-6 kg/C

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