# Homework Help: Motion of Charged Particles

1. Jul 19, 2010

### lwelch70

1. The problem statement, all variables and given/known data

1) Calculate the value of B_z needed for an electron with a speed of 6X10^5 m/s to be deflected to the right in acirle of radius 3cm.

2) Calculate the value of E_x needed for an alpha particle with a speed of 6X10^5 m/s to be deflected to the right in a circle of radius 3cm.

3) Calculate the value of E_x needed for an electron with a speed of 6X10^5 m/s to be deflected to the right by 3 cm.

4) Calculate the value of E_x needed for any particle with a speed of 6X10^5m/s to be deflected in a magnetic field of .0005T.

5) Calculate the radius of the circle in this helix.

2. Relevant equations

r= mv/QBz

Ex = vB

3. The attempt at a solution

So problems 1 and 2 are straight forward plug and play. Got those answers to be 1.14E-4 T and .415 T respectively. Problem 4 is also plug and play to come out to 300 N/C.

Where I get out of what is on problem 3 and 5. Any help/equations to get me started? I hate to look like I haven't tried to solve there I just don't know where to go with these. Just need some help along the yellow brick road.

2. Jul 20, 2010

### lwelch70

Anyone have any ideas?

3. Jul 22, 2010

### AJ Bentley

It doesn't make sense.

Apart from the peculiar mix of Cartesian directions and left/right, I assume the x direction to mean the original direction of travel.
In which case for part 3 the field E_x would be along that same direction and would merely impart additional acceleration. To the right?! - it's meaningless.

I don't see how you answer 4 so confidently either. It just says 'to be deflected' How much? are we to assume it's the same 3cm radius?

The first two parts are reasonable and fairly trivial questions - but the rest of it is garbage.

Is there a diagram? Is that what's missing?