Determining the magnetic force on an electron

[chef99]

Homework Statement

A magnetic field of 0.0200 T [up] is created in a region.a) Find the initial magnetic force on an electron initially moving at 5.00 x106 m/s [N] in the field.b) What is the radius of the circular path? Make a sketch showing the path of the electron.

Homework Equations

F_M = qvB

F_C = F_M

The Attempt at a Solution

[/B]
F_M = qvB

F_m = (1.60 x10^-19C)(5.00 x10⁶)(0.0200T)

F_M = 1.6 x10^-14 C

Using the right-hand rule, point the thumb in the opposite direction of the velocity, as the charge is negative. So thumb points south. The fingers point [up], in the direction of the field and the palm points west.

Therefore the direction of the magnetic force is 1.6 x10^-14 C [west]b)

The electron will move with uniform circular motion.

F_net = F_M -but in circular motion, F_net = F_C

F_C = F_M

mv / r = qB

r = mv / qB

r = (9.11 x10^-31kg)(5.00 x10⁶) / (1.60 x10^-19C)(0.0200T)

r = 1.42 x10^-3m

The electron will experience a uniform circular motion with a radius of 1.42 x10^-3m
I'm pretty sure I have this right, the one thing I'm not very confident about is whether I used the right-hand rule properly or not. Furthermore, assuming that the direction of the magnetic force is [west] is correct, is it in fact [west], or should it be

. The reason I used west is because the magnetic force on the electron was [N], not [up]. Any feedback is appreciated.
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[phyzguy]

I think you did most of it right, but are Coulombs the correct units for force?

 

[NateTheGreatt77]

You did use the RHR correctly, but when you say that the magnetic force on the electron is up [N], this is not correct. When I use the RHR I use my pointer finger to point in the direction of velocity, (since it is the first term in the cross product), then my middle finger points in the direction of the magnetic field(second term B). So with q(v x B) = F, then your thumb will point in the correct direction for the force on a positively charged particle. Since yours is negative, you just take the opposite direction of your thumb (or use your left hand entirely and take the direction of your thumb). With v moving [N], and B pointing [up], you should get your thumb pointing in [E], then you must take the opposite direction since your particle is negative (electron). Otherwise the math is correct. Hope this helps!

 

[chef99]

You did use the RHR correctly, but when you say that the magnetic force on the electron is up [N], this is not correct. When I use the RHR I use my pointer finger to point in the direction of velocity, (since it is the first term in the cross product), then my middle finger points in the direction of the magnetic field(second term B). So with q(v x B) = F, then your thumb will point in the correct direction for the force on a positively charged particle. Since yours is negative, you just take the opposite direction of your thumb (or use your left hand entirely and take the direction of your thumb). With v moving [N], and B pointing [up], you should get your thumb pointing in [E], then you must take the opposite direction since your particle is negative (electron). Otherwise the math is correct. Hope this helps!

Thanks that makes a lot more sense. just to clarify, I got the direction of the magnetic force right, (1.6 x10-14 C [W]) just how I used the RHR was incorrect?