# Force on Charge Moving in Magnetic Field

1. Mar 8, 2009

### Kandycat

1. The problem statement, all variables and given/known data
A proton (mass mp), a deutron (m=2mp, Q = e), and an alpha particle (m = 4mp, Q = 2e) are accelerated by the same potential difference V and then enter a uniform magnetic field B, where they move in circular paths perpendicular to B. Determine the radius of the paths for the deuteron and alpha particle in terms of that for the proton.

2. Relevant equations
r = mv/qB

m=mass
v=velocity
q=charge
B=magnetic field

3. The attempt at a solution
I thought V = delta PE = delta KE = delta (1/2)mv2

And then I got confused.

2. Mar 8, 2009

### rl.bhat

When the charged particles are accelerated in a potential difference V,energy acquired by them is given by qV, where q is the charge on it. And it can be equated to its KE. First of all find the velocity of each particle and substitute in the formula for radius and compare them.

3. Mar 8, 2009

### Kandycat

Is the charge of a proton 1.6E-19 C?

4. Mar 8, 2009

### rl.bhat

Yes. But to solve this problem this value in not needed, because you are comparing radii.