Right Hand Rule #2 Homework: Answers and Explanations

[dinhjeffrey]

Homework Statement

#30

Homework Equations

right hand rule #2

The Attempt at a Solution

when i did it, i pointed my thumb to the right, because the current is going to the right. and when i wrapped my hands around the wire until i reach the electron, i go the magnetic force going into the page. but since the charge is negative, i got out of the page. however the answer is E) to the right, but i don't know why.

 

[ojs]

The direction that you are talking about is the direction of the magnetic field the wire is producing, not the force on the electron.
You have the direction of the magnetic field correct, now try to use the right hand rule again to find the direction of the force (hint: the sign of the charge comes into play here).

 

[dinhjeffrey]

okay so i applied the right hand rule:
thumbs pointing to the right because current is to the right
fingertips pointing into the page
and my palm(force) is pointing up
but since its negative force would be going down?

 

[ojs]

Nope, not correct.

I think we have to review the right hand rule a bit.

There are two ways to use the right hand rule, like with the current in the wire, you did that correctly, let the thumb go in the way of the current, bent your fingers around the wire and found the direction of the magnetic field that way (they follow the direction of the fingers).
But when finding the force on a moving charge in a magnetic field it is a bit different, then we are using the equation F = q v x B (here x is the cross product). In finding the direction of the vector from the cross product you only use the first three finger, put the first vector (in our case velocity) along the index finger, the second vector (the magnetic field) along the middle finger and the resultant (the force) is in the direction of the thumb. But when the charge is negative the direction changes 180°.

 

[dinhjeffrey]

ohh okay i got it. i was confused because i used the direction of current for the first vector instead of velocity.thanks, i like how you answer all my questions ;DD