(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

In a cathodic ray tube, the canon launches a circular electron beam on the screen. The beam has a 0.22 mm diameter, the electrons have a kinetic energy of 25 keV and 5.6*10^14 electrons reach the screen each second. Find the magnetic field produced by the beam on a point located at a 1.5mm distance of the beam axis.

The answer is 12 nT

2. Relevant equations

I know that the magnetic field of a circular arc is

B = (u*i*angle)/(4*Pi*distance) but in this case I don't have an angle so im pretty sure this is not the correct formula

Also we could integrate using the biot savart rule but we don't have the limits of integration.

3. The attempt at a solution

I have found the current by using the fact that 5.6*10^14 electrons reach the screen each second. By converting electrons to coulombs, I get 8.97 * 10^-5 Amperes. Then I am stuck, I have no idea how to continue

thank you

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# Homework Help: Magnetic field problem

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