# Homework Help: Electric and Magnetic Field lines

1. Nov 7, 2015

### kilnvzol

1. The problem statement, all variables and given/known data
The figure shows crossed uniform electric and magnetic fields and, at a certain instant, the velocity vectors of the 10 charged particles listed in the table. (The vectors are not drawn to scale.) The speeds given in the table are either less than or greater than E/B (see Question 1). Which particles will move out of the page toward you after the instant shown in the figure? (Several choices may be correct.)

2. Relevant equations
Right/Left Hand Rule (RHR) & (LHR)

3. The attempt at a solution
Not sure what I'm missing because based on the RHR and LHR 1 and 2 are going out of the page, 3-6 are going into and 7-10 are 0, I think.
It said my answer was wrong when I just put 1&2.
Please help I only have one attempt left and I really don't understand. ;-;

Last edited: Nov 7, 2015
2. Nov 7, 2015

### TSny

Many of your answers are incorrect. It appears to me that you might be neglecting the force due to the electric field and also neglecting the fact that some of the particles have negative charge.

For example, can you explain in detail how you conclude that particle 1 will move out of page?

3. Nov 7, 2015

### kilnvzol

Isn't the magnetic field, B, the finger tips and the thumb the current or velocity vectors and the palm tells where the force is coming out of? And RHR is for positive charge and LHR is for negative charge?

So since the charge is positive you use the RHR and since the magnetic field is going left you point your right hand fingers to the left of the page and you point your thumb toward the top of the page and you get the force going out of the page?

4. Nov 7, 2015

### TSny

Yes, that's right for the B field. But what about the force from the E field?

5. Nov 7, 2015

### kilnvzol

Would they all be going into the page?

6. Nov 8, 2015

### TSny

Does the direction of the electric force depend on the sign of the charge?

7. Nov 8, 2015

### kilnvzol

Yes, because whatever direction the force is for one charge it should be the opposite for the other. So if 3 was into 5 should be out of.

8. Nov 8, 2015

### TSny

Yes. So, let's check your work for particle 1. What is the direction of the electric force? What is the direction of the magnetic force? And what is the direction of the net force?

9. Nov 8, 2015

### kilnvzol

The electric force goes into the page
The magnetic force goes to the left of the page.
The net force goes into the page?

10. Nov 8, 2015

### TSny

Yes
No. Use the RHR.

11. Nov 8, 2015

### kilnvzol

Is it going to the right of the page?

12. Nov 8, 2015

### TSny

In what direction did you point your fingers and in what direction did you point your thumb?

13. Nov 8, 2015

### kilnvzol

I pointed my fingers into the page and thumb to the top of the page.

14. Nov 8, 2015

### TSny

Point your fingers in the direction of the B field.
Yes.

15. Nov 8, 2015

### kilnvzol

So its out of the page?

16. Nov 8, 2015

### TSny

Yes, the magnetic force is out of the page. So, next you need to determine the direction of the net force.

17. Nov 8, 2015

### kilnvzol

Would the electric force and the magnetic force cancel for the net force?

18. Nov 8, 2015

### TSny

If the magnetic force happened to be stronger than the electric force, what would be the direction of the net force?

How are you going to decide which force is stronger for particle 1? Have you used all of the information in the table?

19. Nov 8, 2015

### kilnvzol

Is the strength of the force determined by the speed?

20. Nov 8, 2015

### TSny

For one of the forces the force is related to the speed. For the other force it isn't.