Volume charge density across a potential difference

samedi 30 août 2014

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



A 1.0 μA proton beam is accelerated across a potential difference of 1.0 kV. Assume the beam has uniform current density over a diameter of 2.0 mm, and zero outside.



Find: volume charge density in the beam, (HINT use λ=I/v where λ= charge/ unit length)



The radial electric field intensity inside and outside of the beam.



2. Relevant equations



λ=I/v, λ=Q/unit length, ρ_v=Q_total/V, KE=1/2mv^2



3. The attempt at a solution





I approached the first part by finding kinetic energy using know values for mass and charge then rearranging to find velocity. I then inserted velocity into the hint equation to find total charge then used volume density= total charge over potential difference. However I don't think this last approach is correct.



For the second question I'm so confused. I know E=-∇V but V is a scalar so my other approach was to show that it had zero electric field due to no charge.



Any help would be so appreciated! Thanks!





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