Right hand rule? magnetic fields!

Question

this is another true false that is driving me nuts. i know electrons are opposite how protons reflect...but this is crazy! thanks for your help!

In case #1 the magnetic field points out of the page, toward you. In case #2 the magentic field points into the page, away from you. Answer True or False.

A proton entering the field B1 from the west is deflected to the north.

An electron entering the field B2 from the east is deflected to the south.

An electron entering the field B2 from the south is deflected to the east.

A proton entering the field B2 from the north is deflected to the east.

A proton entering the field B1 from the west is deflected to the south.

Answer 1

Force = qv x B

Right hand rule: Fingers x Palm = Thumb

Put the fingers of your right hand in the direction of the velocity.

Put your palm in the direction of the magnetic field.

Your thumb will point in the direction of the force on a positive charge.

Flip that for a negative charge.

So for the first one, the proton comes from the west, so fingers point east.  Palm points out of the page.  So the force (your thumb) is south.  So it's false.

Now you can do the rest.  Don't forget to flip the answer for a negative charge.

Funny story: under pressure during a test, some students will use their left hands to do the RHR (because they are holding their pencils in their right hand).  Back when I was a student, our class had a debate with the teacher about whether it would be cheating to write "Wrong hand" in magic marker on your left hand.  He decided it would be cheating to do it before the test (like bringing in notes), but as soon as the test started, you could legally do it (like writing notes on scratch paper during test).

Answer 2

1)False; deflected south

2)False;deflected north

3)True

4)True

5)False; deflected north

In every case the charged particle enters in the plane of the page (call it the x-y plane). In both B field cases the B field points perpendicular to the page.

The deflection will be at right angles to the plane formed by the velocity vector and the B field vector. For + charges it is by the right hand rule. For - charges it is the opposite direction of the right hand rule.

Right Hand Rule = Curl fingers of right hand as if rotating vector v into vector B. Thumb is in the direction of the force (deflection)