J. J. Thomson is best known for his discoveries about the nature of cathode rays

Question

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 q of an ion. The spectrometer consists of two regions as shown in the figure. I Floured 1) In the first reason an electric field After being accelerated to a speed of 1.81 x105m/s , the particle enters a uniform magnetic field of strength 0.900T and travels in a circle of radius 35.0cm (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 particle. Express your answer numerically in kilograms per coulomb.

Explanation / Answer

Part A:

Speed of particle, v = 1.81 * 10^5 m/s

Magnetic field strength, B = 0.900 T

Radius of circle, r = 35.0 cm

                          = 35.0 * 10^-2 m

The expression for m/q is,

             m/q = rB/v

                    = (35.0 * 10^-2 m)(0.900 T) / (1.81 * 10^5 m/s)

                    = 1.74 * 10^-6 kg/C

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