# Electric and Magnetic Field Parallel

1. Apr 22, 2015

### navm1

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

2. Relevant equations
F=qE+qv x B

3. The attempt at a solution

The electric and magnetic fields are parallel, so the magnetic force will be in the j direction and the electrostatic force will be in the k direction. If the magnetic force was acting alone it would be cyclotron motion but since the electrostatic force is acting too does this mean it is moving in a helical path? I'm having some difficulty thinking about where the electric field is pointing and how to draw it properly. Thanks

for part b) I can find the acceleration using (qE)/m and plug into a distance equation but im not sure if that is what I'm being asked to do.

Last edited: Apr 22, 2015
2. Apr 22, 2015

### Staff: Mentor

Sort of helical, as it is always accelerating in k-direction.

3. Apr 22, 2015

### navm1

Thanks. For part b, if I use v_0t+1/2*((qE/m))t^2 as the position of the proton along the z direction. Then for part c I can calculate the period and then put '3T' into the equation I found in part b to find the particles position. Am I on the right track with this?

4. Apr 22, 2015

### Staff: Mentor

What is v_0 in z direction?
Right.

5. Apr 23, 2015

### navm1

v_0 in the z direction is 0 so z=1/2*((qE/m))t^2 = 1/2* ((1.6x10^-10)(5000))/1.673x10^-27)*(1.3x10^-4)^2 = 4041m = 4km ?

6. Apr 23, 2015

### Staff: Mentor

Is that the distance after one or after three revolutions?

7. Apr 23, 2015

### navm1

my mistake, that is one revolution so three should be 36431metres

8. Apr 23, 2015

Right.