Mass Spectrometer J. J. Thomson is best known for his discoveries about the natu

Question

Mass Spectrometer

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.

Part A

After being accelerated to a speed of 1.95×105 m/s , the particle enters a uniform magnetic field of strength 0.800 T and travels in a circle of radius 32.0 cm (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

here,

r = 32 cm = 0.32 m
v = 1.95 * 10^5 m/s
B = 0.800 T

From Circular Motion Centripital force will be provided by Magnatic Force Therefore We get,

MV^2/R = B*q*V
M/Q = BR/v
M/Q = ( 0.0800 * 0.32 ) / (1.95 * 10^5)

M/Q = 1.3128*10^-7 Kg/C

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