# Homework Help: Magnetic Force on moving ion?

1. Feb 9, 2005

### triplezero24

Ok, an ion experiences a magnetic force of 6.2X10^-16 N when moving in the positive x direction, but no force when moving in the positive y direction. What is the magnitude of magnetic force exerted on the ion when it moves in the x-y plane along the line x=y? Assume the ions speed is the same in all cases.

I know that for this problem F=qvB sin theta. Because the ion travels on the line x=y, then the theta angle is 45. Other than that I have no clue.

Thanks again for any help.

2. Feb 9, 2005

### StatusX

break it up into an x component and a y component velocity and find the force for each.

3. Feb 10, 2005

### triplezero24

It says the speed is the same in all cases.

4. Feb 10, 2005

### vincentchan

so what?
break it up into an x component and a y component velocity and find the force for each.
for sure v_x and v_y is not equal to v.... but can you find v_x and v_y in term of v using the P******* theorm? (really have no idea how to spell that word)

5. Feb 10, 2005

### Davorak

StatusX means use vector notion instead of F=qvB sin theta.

$$F= q \vec{v} \times \vec{B} =( v_y B_z - v_z B_y )\hat{x} + (v_z B_x - v_x B_z )\hat{y} + (v_x B_y - v_y B_x)\hat{z}$$

Some terms will be zero though if $$\vec{B}$$ is perendicular to $$\vec{v}$$

6. Feb 10, 2005

### Staff: Mentor

This should tell you two things:
(1) The direction of the magnetic field (B)
(2) The value of qvB (apply $F = qvB sin \theta$, where $\theta$ is the angle between v and B)

Once you've figured out (1) and (2), all you need to find your answer is to again apply $F = qvB sin \theta$ with this new angle. What angle does the ion velocity make with the B field when it travels the line x=y?