How Could She Not Like you? You have a Magnetic Personality!

Hi everyone,

1. As a recommendation, you might want to check out questions 7 and 8 for more practice with the right/left hand rule. I'll post the solutions below.


As promised, here is a video of a magnetically levitated frog.


You can search on Google for more interesting videos if you enter 'magnetic levitation'.

The magnetic force simulator is located at
http://www.physics.upenn.edu/courses/gladney/phys151/lectures/lecture_feb_24_2003.shtml

You must stop and reset the simulation each time you change something to see the effect of the change.

Here are the HW solutions from the handout:
1. 3.84 x 10^-14N
2. into page, towards left, towards top of page, towards right, force is zero!
3. For this problem, you have to say which direction you are assuming each vector is pointing towards. If velocity is towards the right side of the page, and B is 30 degrees above the velocity towards the top of the page, then you must use the perpendicular component of one vector along another and the right hand rule. This results in a 3.2 x 10^-16N force directed out of the page for (a).
b) 1.92 x 10¹¹m/s^2
c) The force has the same magnitude as (a) but the force and acceleration are directed into the page. The acceleration of the electron would be 3.51 x 10¹¹m/s^2
4. 9.375 T towards top of page

Solutions to 7,8:


7. To find the direction of the force on the electron, we point our fingers in the direction of v and curl them
into the magnetic field B. Our thumb points in the direction of the force on a positive charge. Thus the
force on the electron is opposite to our thumb.
(a) Fingers out, curl down, thumb right, force left.
(b) Fingers down, curl back, thumb right, force left.
(c) Fingers in, curl right, thumb down, force up.
(d) Fingers right, curl up, thumb out, force in.
(e) Fingers left, but cannot curl into B, so force is zero.
(f) Fingers left, curl out, thumb up, force down.

8. We assume that we want the direction of B that produces the maximum force, i. e., perpendicular to v.
Because the charge is positive, we point our thumb in the direction of F and our fingers in the direction
of v. To find the direction of B, we note which way we should curl our fingers, which will be the direction
of the magnetic field B.
(a) Thumb out, fingers left, curl down.
(b) Thumb up, fingers right, curl in.
(c) Thumb down, fingers in, curl right.