I DESPERATELY need Physics Help!!-Please??

Question

Alpha particles (Helium atoms with the two electrons missing) of charge q = +2e and mass m = 6.6E-27 kg are emitted from a radioactive source at a speed of 1.46E+7 m/s. What magnetic field strength would be required to bend these into a circular path of radius r = 0.16 m?

Protons move in a circle of radius 4.40 cm in a 0.557 T magnetic field. What value of electric field could make their paths straight?

I need to know how to answer these problems. I am really lost on how to solve these magnetism problems.

Answer 1

Lorentz magnetic force qvB acts as centripetal force mv^2 /r
Magnetic field B =mv / qr=6.6E-27 *1.46E+7 / 3.2E -19 *0.16
=1.882 tesla

For straight path and uniform motion of charged particle entering perpendicularly into MUTUALLY PERPENDICULAR electric field E and magnetic field B
electric field force=magnetic field force
qE=qvB gives v=E/B also mv^2/ r = qvB gives

the velocity v=qBr / m = E/B

E = qrB^2 / m = 1.6*10^-19*0.044*0.557*0.557/1.67*10^-27
=1.307*10^6 newton /coulomb

Answer 2

The magnetic force on a charge moving at velocity V in a magnetic field B is Fm = q*V X B. This will cause the charge to move in a circle such that the centrifugal force Fc = m*V^2/r. Equate these forces to get

q*V*B = m*V^2/r, or B = (m*V/q*r)

It comes out 1.88 tesla

For the second part, compute the force on the proton. First find the velocity from the above formula solved for V:

V = q*B*r/m. Use this to compute the force F = m*V^2/r then calculate the electric field to produce this force E*q = Fe; E = Fe/q

For the proton, m = 1.67*10^-27 kg, q = 1.6*10^-19 coul

NOTE: Values edited to correct arithmetic errors:

V = 2.34810^6 m/sec
Fe = 2.093*10^-13 N
E = 1.308*10^6 volt/m

You don't have to worry about relativistic effects because the velocities in both cases are much less than light velocity (=3*10^8 m/sec)

Answer 3

Well, you're dealing with the Lorentz force, centripetal acceleration, and, depending on the course level, relativistic mass. Reread the chapter on this concepts.