Vector evaluation & Lorentz force law

[Roodles01]

Homework Statement

An electron in a magnetic field B=2.0T(e_x-e_z) has velocity v=(2.5x10⁷ ms-1 (e_x-e_y)
a) calculate magnetic force on electron at that instant
b) what is the magnitude of this force

Homework Equations

I am using the Lorentz force law.
F = q(vXB)
& evaluating the directions by vector

My argument is that the e_y term is negative, but another person evaluates this as positive. Please confirm whether I'm right or wrong.

This affects the outcome of magnitude of force, too.

The Attempt at a Solution

F = -e 2(2.5x10⁷) (e_x-e_z)* (e_x-e_y)

I ex ey ez I
I 1 . -1 . 0 I
I 1 . 0 . -1 I

= ex((-1x-1)-(0x0)) + ey((1X-1)-(0x1)) + ez ((1x0)-(-1x1))
= e_x - e_y + e_z)

so
F = -8x10-12 (e_x - e_y + e_z)

 

[rude man]

Better believe your friend about the sign of the j term! (Re-check your determinant).

 

[Roodles01]

Ah! Having looked at it, I found that I didn't change the sign for the second term.
So simple it's annoying.
Thank you.

 

[rude man]

Ah! Having looked at it, I found that I didn't change the sign for the second term.
So simple it's annoying.

Welcome to the club!