Cosmic Ray Protons

1. Feb 4, 2008

[SOLVED] Cosmic Ray Protons

1. The problem statement, all variables and given/known data

Earth's atmosphere is constantly being bombarded with cosmic ray protons that originate somewhere in space. If the protons all pass through the atmosphere, each square meter of Earth's surface would intercept protons at at the average rate of 1500 protons per second. What would be the electric current intercepted by the total surface area of the entire planet?

2. Relevant equations
Surface Area of sphere=4*pi*r^2

3. The attempt at a solution
Okay, I don't even understand what this question is asking.
It wants to know the total # of protons the surface will intercept. I get that. But then it gives a rate protons per second, but does not give a tine interval.

I am lost on this one :/

2. Feb 4, 2008

Staff: Mentor

All you need is the rate at which charge is intercepted, which is given. (What's the definition of current?)

3. Feb 4, 2008

BishopUser

From how I am understanding it. Current is defined as flow of charge (charge/time). So if they are asking for current it would be on a per unit time basis. I think the main part of the problem is how to convert protons/sec into charge/sec.

4. Feb 4, 2008

Shooting Star

Why would that be a problem? Does mankind not know the charge of a proton yet?

5. Feb 4, 2008

All I can find for a definition of current is $i=\frac{dq}{dt}$ where i is in ampheres and dq is in Coulomb's. . . hmmm. So I would need to convert $1500*4\pi R_{earth}^2$ into Coulombs?

6. Feb 4, 2008

BishopUser

uhh mankind does, but maybe some students don't (as witnessed by this thread)?

7. Feb 4, 2008

Staff: Mentor

You're on the right track. $1500*4\pi R_{earth}^2$ gives you protons per second. What's the charge of a proton? The current would be in Coulombs/second or Amps.

8. Feb 4, 2008

Isn't it just 1e? I don't follow. . . or are you going to follow that question with "now how many e are in one Coulomb" . . . cause if you are, I would have to say 6.25(10^18) and then I would have to do a simple chain conversion and get the right answer!!

Thanks,
Casey

9. Feb 4, 2008

Staff: Mentor

I would have said: What's the proton charge in Coulombs? e = 1.60217646 × 10-19 C. (But same difference.)

10. Feb 4, 2008

Shooting Star

Point taken (somewhat) . I am sure that the student knew the charge of a proton. The problem lied in correlating the number/sec and the corresponding charge/sec.

11. Feb 4, 2008

Staff: Mentor

As Doc mentioned, you're on the right track.

If N particles/sec, each of charge e+, pass some point, the current I = Ne.

12. Feb 4, 2008