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

[chocolatePI]

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 ?

 

[gneill]

What is the definition of current?

 

[chocolatePI]

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?

 

[gneill]

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?

 

[chocolatePI]

q= C - coloumbs
t= s- seconds
meaning charge A = C/s

which equation would i use to put this into ?

 

[gneill]

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?)

 

[chocolatePI]

so 2.8x10-6 / 1.6x10-19 for part a?

 

[gneill]

so 2.8x10-6 / 1.6x10-19 for part a?

Put in the units and you'd be correct.

 

[chocolatePI]

any tips on part b?

 

[gneill]

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...