How Many Electrons Strike the Screen in 1 Hour?

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SUMMARY

The discussion centers on calculating the number of electrons striking a television screen in one hour, given a beam current of 32mA and electron speed of 4.2x107 m/s. The total charge over one hour is calculated as 115.2 Coulombs, resulting in approximately 7.2x1020 electrons. Additionally, the challenge of determining the number of electrons in the beam at any instant is addressed, with calculations indicating that only a fraction of the electrons are in motion at any given moment.

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  • Understanding of electric current and charge (Coulombs)
  • Familiarity with electron charge (1.6x10-19 Coulombs)
  • Basic knowledge of kinematics (speed and distance)
  • Ability to perform calculations involving scientific notation
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  • Explore the concept of beam current in cathode ray tubes
  • Learn about the relationship between charge, current, and time in electrical circuits
  • Investigate the principles of electron motion in vacuum tubes
  • Study the effects of electron density and velocity in beam dynamics
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Students in physics, electrical engineering professionals, and anyone interested in the operation of cathode ray tubes and electron behavior in electric fields.

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The beam current in a television tube is 32mA. The electrons travel at a speed of 4.2x10^7m/s through a distance 21cm.

a) The number of electrons striking the screen in 1 hour is?

I did: Q=IT = 0.032A x (60x60)s = 115.2 C

Number of electrons = 115.2/1.6x10^-19 = 7.2x10^20

b) The number of electrons in the beam at any instant is?

I tried doing the same as above but for one seconds but couldn't work it out at all. Anyone give me a clue?
 
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The length of your beam is .21 m.

In 1 sec you would have a beam column containing of .032ma.

A 1 sec column would contain 3.2*10-5*6.241*1018 electrons of which only .21/4.2*107 are actually in motion within the tube.
 

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