Right hand rule

[Aiicha]

Hey Guys,

I feel kinda dumb but I am having a hard time mastering this. For example:

If I want a magnetic field to counter the effects of an electric field and my electric field is pointing to the right and I have a positive charge in that electric field moving to the right, what's the direction of the magnetic field?

Ok so I get that I need my magnetic field force to point to the left and when I do that my magnetic field fingers curl and point out of the page, but that leaves my thumb pointing up, not to the right. If I point my thumb to the right , my palm (force) looks like its pointing up. What the deal? Any help is much appreciated.

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[ballofnerves]

You cannot counter the electric field with a magnetic field. This is because the magnetic force will always act perpendicular to the direction of the charge's motion.

What you want is for the magnetic field to act directly against (i.e., antiparallel) to the electric field. This is simply not possible. Adding a magnetic field will simply cause the moving charge to enter circular motion, but cannot get the charge to stop altogether.

 

[Aiicha]

Sorry, what I meant was that I want the force of the magnetic field to counter the force of the electric field, does that make more sense? like the electric field points to the right, so I want the force of my magnetic field to point to the left?

 

[ballofnerves]

Sorry, what I meant was that I want the force of the magnetic field to counter the force of the electric field, does that make more sense? like the electric field points to the right, so I want the force of my magnetic field to point to the left?

Sorry, I must not have been very clear

The electric force causes the charged particle to accelerate to the right. The magnetic force cannot point to the left if your charged particle is moving to the right. The force could only be directed perpendicular to its motion, not directly against it. For example, the magnetic force could point out of the page or into the page, but not to the right or to the left. So in this regard, the magnetic force cannot counter the electric force.

Hopefully this answers your question...

 

[Aiicha]

Thanks, I see what you mean. Looking back at the question I was confused about the velocity. My instincts about RHR were right but I was miss reading the material. Thanks for your help.

 

[Bu2009]

I use the right hand rule for positive charges ie protons
Left hand rule for negative charges ie electrons.

maybe that could help u... if you have the TPR physical sciences book, the EM section is like 80 pages, but its a big help it has tons of worked out examples on probably 95% of the questions types that u can expect out of this section.

 

[lhenslee]

Don't forget that electrons and protons run opposite each other, and current is referring to proton flow.