Right Hand Rule - Mcat

This is everything you need to know about the Right Hand Rule (RHR), or rather the two versions thereof. One or the other of them applies any time you are finding a direction (whether of field, force, acceleration, or even something else), and charges are moving.

I detail the flat hand method — no sticking fingers in different directions perpendicular to each other.

There are two related right hand rules. Let’s say: Right Hand Rule 1 (RHR1) — used to determine the direction a charged particle, moving in a magnetic field, will be pushed; Right Hand Rule 2 (RHR2) — used to determine the direction of a magnetic field created by the movement of charges.

There are three parts of your hand to remember, and I try to make it is easy as possible:

1. Fingers = Field: stick your fingers (of your right hand) in the direction of the magnetic field; if you aren’t told the field (i.e., you are doing RHR2), the fingers are eventually going to tell you its direction. In other words, fingers = the first field you encounter in the problem. Remember, this is only for magnetic fields; electric fields have nothing to do with magnetism problems.
2. Thumb = hitchhike, in the direction of motion. Motion of what? Of the thing in the problem that’s moving (the charged particle or particles; if there’s just a current given, not particles, then that current would be the movement, by convention in the positive direction even though it’s usually the movement of negative particles in the opposite direction). In other words, the first motion you encounter in the problem. (Note: the direction it’s going now, not the direction of its acceleration.)
3. Palm = Push. Your palm will face in the direction that a positively-charged particle will be pushed by the magnetic field. For RHR1 problems, this is usually what the problem asked you to figure out. For RHR2 problems, it doesn’t really apply but it still works: a positively-charged particle moving in the same direction as the current will be pushed toward the wire by the magnetic field.

So, if asked to figure out the direction a particle is pushed, stick your fingers in the direction of the magnetic field, and hitchhike in the direction the particle is moving. Your palm is now trying to push the charge, in the appropriate direction. You just used RHR1.

If asked to make a magnetic field, hitchhike in the direction of the moving charges (or the current); your fingers, which now are allowed to curl, show the direction of the field, which curls around the path of the charges. You just used RHR2.

Related issues:

• The magnetic field does zero work, always. This is because it is always perpendicular to motion, turning the particle rather than speeding it up or slowing it down. That’s why we can kind of throw it in there at the end of electrostatics: it has no effect on the energy of anything.
• It is possible to use the analogous left hand rule to solve problems for negative charges moving in magnetic fields, but I recommend against it. Use RHR, of whichever type, and for negative charges or currents the answer is the opposite direction.
• Electric fields do not create magnetic fields; these two are unrelated for your purposes. You’ll know this if you try to apply RHR inappropriately — you can’t stick your fingers in two different directions.