ADDITIONAL PROBLEMS Question 19.la: The figure illustrates a velocity selector,

Question

ADDITIONAL PROBLEMS Question 19.la: The figure illustrates a velocity selector, in which charged particles of a specific speed pass through undeflected while those of greater or lesser speeds are deflected either to the left or to the right. After leaving the velocity selector, particles enter a purely magnetic field. A particle?s radius of motion is then used to find the mass-to-charge ratio of the particle, which In turn can identify it. Taken altogether, this device is called a mass spectrometer. The illustrated electric field is directed to the right with magnitude 1.95 x 10 V/m and the magnetic field is directed into the screen with magnitude 0.560 T. (a) Determine the speed y of the undeflected charged particle. (b) After passing through the velocity selector, the charged particle moves in a circular path with a radius of r = 6.49 mm. Determine the particle?s mass-to-charge ratio.

Explanation / Answer

a)

For velocity selector ,

magnetic force = electric force

qV B = qE

V = E/B = 1.95 x 105 / 0.560

V = 3.48 x 105 m/s

b)

Using the formula

r = mv/qB

r = radius = 6.49 mm = 6.49 x 10-3 m

v = speed = 3.48 x 105

B = magnetic field = 0.560

(6.49 x 10-3 ) = (m/q) (3.48 x 105 / 0.560)

m/q = 1.04 x 10-8

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