How Many Electrons Does a Cathode Ray Tube Emit Per Second?

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Homework Help Overview

The discussion revolves around a problem related to the emission of electrons from a cathode ray tube, specifically focusing on calculating the number of electrons emitted per second based on given current and electron speed. The subject area involves concepts from electromagnetism and particle physics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the definition of current and its relation to charge flow, questioning how to apply the given information to the problem. There are attempts to clarify the units of charge and time in the context of the equations provided. Some participants suggest using the current value to determine the number of electrons emitted per second based on the charge of an electron.

Discussion Status

The discussion is active, with participants sharing insights about the relationship between current and charge. Some guidance has been offered regarding the calculations needed for part a of the problem, while part b remains open for exploration. Multiple interpretations of the problem are being considered.

Contextual Notes

Participants are working within the constraints of the problem statement, which includes specific values for current and electron speed, as well as the fundamental charge of an electron. There is an emphasis on understanding the underlying principles rather than arriving at a final answer.

chocolatePI
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Homework Statement


The beam of electrons in a cathode ray tube contains electrons traveling at 8.4x106 ms-1 and the current throgh the tube is 2.8 micro A.
a) how many electrons are emitted per second from the cathode of the tube
b) what is the number of electrons per unit length of the beam?

Homework Equations


I=nAvq
q=16.x10-19
there are more equations involved in the proof of I=nAvq which might be needed

The Attempt at a Solution


possibly involves Q=nAvte ?
 
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What is the definition of current?
 
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current = rate of flow of charge
I=q/t
but I am not sure how to use the information in the question in this context?
 
chocolatePI said:
current = rate of flow of charge
I=q/t
but I am not sure how to use the information in the question in this context?
What units might you assign to the q and t in your formula?
 
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q= C - coloumbs
t= s- seconds
meaning charge A = C/s

which equation would i use to put this into ?
 
chocolatePI said:
q= C - coloumbs
t= s- seconds
meaning charge A = C/s

which equation would i use to put this into ?
You're given the current value. So you know how many Coulombs per second are flowing from the cathode. How many electrons per second does that represent? (Whats the charge on every electron?)
 
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so 2.8x10-6 / 1.6x10-19 for part a?
 
chocolatePI said:
so 2.8x10-6 / 1.6x10-19 for part a?
Put in the units and you'd be correct.
 
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any tips on part b?
 
  • #10
chocolatePI said:
any tips on part b?
What are your thoughts? See if you can imagine a scenario where you can count the number of electrons over a known distance. Suppose, for example, the beam is switched on for exactly one second...
 

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