Question

A Tevatron can accelerate particles to energies in the TeV range (1.00 tera −eV = 1.00×10^12 eV ). Its circumference is 6.40 km, and in a certain medical experiment protons will be accelerated to energies of 1.25 MeV and aimed at a tumor to destroy its cells.

1) How fast are these protons moving when they hit the tumor?
v = 1.55×107 m/s (correct answer)
2) How strong must the magnetic field be to bend the protons in the circle indicated?

So I know that F = qv x B and that
B = mu*I / 2pi*r
The answer needs to be B equals some amount in T, but I don't have the charge (I). What should I do?

Answer 1

google these ... mass of proton, charge of proton, Joules to MeV

Answer 2

current*, not charge

I'm not sure I can concert the voltages into amps without knowing power

Answer 3

one MeV is 1.60E-13 Joules

proton mass is 1.67E-27 kg

1/2 m v^2 = 1.25 * 1.60E-13 J = 2.00E-13

v^2 = 2 * 2.00E-13 / 1.67E-27

v = 1.55E7 m/s

proton charge is 1.60E-19 C
... same as electron, opposite polarity

current is charge per unit time past a given point ... C / s

the circumference of the ring is
... 6.40E3 m

the current from a proton is
... (1.60E-19) / (6.40E3 / 1.55E7)