In the neck of the picture tube of a certain black-and-white television set, an

Question

In the neck of the picture tube of a certain black-and-white television set, an electron gun contains two charged metalic plates 3.15 cm apart. An electric force accelerates each electron in the beam from rest to 8.90% of the speed of light over this distance. (Ignore the effects of relativity in your calculations.)
(a) Determine the kinetic energy of the electron as it leaves the electron gun. Electrons carry this energy to a phosphorescent material on the inner surface of the television screen, making it glow.

Explanation / Answer

kinectic energy of electron = mv2/2

m = mass of electron = 9.11 x 10-31kg

v =8.9 x velocity of light / 100 = 8.9 x 3 x 108 / 100 = 2.67 x 107 m/s

kinetic energy = 9.11 x 10-31 x (2.67 x 107)2 /2 = 32.47 x 10-17 J = 2029.51eV

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