# Homework Help: Invisible's Homework House

1. Dec 4, 2004

### Invisible101

Hi, I need help with this question:

An ion with a charge-to-mass ratio of 1.10 x 10^4 C/kg travels perpendicular to a magnetic field (B = 9.10 x 10^-1 T) in a circular path (R = 0.240 m). How long does it take the ion to travel one revolution?

I've found the speed that it travels....then what? How would I find the distance that it travelled? Do I use the circumference?

I've decided....instead of posting a thread everytime I need help, I'm just going to have one thread and this is where I'll post my questions.

2. Dec 4, 2004

### Tide

If the ion travels in a circular path then the distance it travels in one revolution must be the circumference of the circle.

3. Dec 4, 2004

### Invisible101

This is what I did:

q/m = vB┴r
(1.10 x 10^4 C/kg)(9.10 x 10^-1 T)(0.420 m) = v
v = 2402.4 m/s

C = (pie)d (I don't know how to make the symbol)
C = (pie)(0.480 m)
C = 1.507...m

t = d/ = 1.507...m/2402.4 m/s = 6.28 x 10^-4 s

Is this right?

4. Dec 4, 2004

### Tide

I think you switched digits in R. You stated originally that R = 0.24 m but you seem to be using R = 0.42 in your calculation.