A cathode-ray tube (CRT) is an evacuated glass tube. Electrons are produced at o

Question

A cathode-ray tube (CRT) is an evacuated glass tube. Electrons are produced at one end, usually by the heating of a metal. After being focused electromagnetically into a beam, they are accelerated through a potential difference, called the accelerating potential. The electrons then strike a coated screen, where they transfer their energy to the coating through collisions, causing it to glow. CRTs are found in oscilloscopes and computer monitors, as well as in earlier versions of television screens.

If the accelerating potential is 89.0 V, how fast will the electrons be moving when they hit the screen?

Explanation / Answer

The decrease in potential energy of the electrons = increase in kinetic energy

so V*q = 1/2*m*v^2

so v = sqrt(2*V*q/m) = sqrt((2*89.0*1.60x10^-19) / (9.11 *10^-31)) = 5.59 * 10^6 m/s

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