# magnetic fields physics II?

A uniform magnetic field is directed towards the positive x-axis as shown in the figure. An alpha particle (Helium nucleus) enters the field traveling at 3 x 106 m/s in the negative y-direction.

i) Calculate the radius of the circular path executed by the alpha particle.

ii) as seen from the right (i.e. along x-axis towards the origin), will the circular path be clockwise or counterclockwise?

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&sou...

It's number one on exam III.

### 1 Answer

- Xavier DubonLv 47 years agoBest Answer
(i) the particle undergoes the electromagnetic force F = q v X B

where (v is the velocity and B the field, all are vectors) and q= 2e

F is orthogonal to v then the work of F is 0

And If you neglect the weight of the particle, you can write (a is the acceleration):

m a = q v X B =>value of a: a=q/m v B

work of F is 0 => the magnitude of v is constant

the motion is circular and uniform, the a= V^2 / R = q/m vB

then R = mv/(qB) then use your values..

(ii) the velocity is always orthogonal to B... and use the right hand rule to find the direction of the path : which is clockwise