Answer to Question #339574 in Electricity and Magnetism for soph

Question

A proton makes a (radius = 30.0 cm) circular orbit in a 2.5 T magnetic field. What is the velocity of the proton?

mass of proton = 1.67x10^-27 kg, e = 1.602x10^-19 C

Answer 1

$evB=\frac{mv^2}r,$

$eBr=mv,$

$v=\frac{eBr}m=0.72\cdot 10^8~\frac ms.$