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OmegaFury

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## Homework Statement

A point charge of q

_{1}=3.6nC is moving with speed 4.5 x 10

^{7}m/s parallel to the y-axis along the line x=3m. The magnetic field produced by this charge at the origin when it is at the point x=3m, y=4m is approximately:

## Homework Equations

vector B= (magnetic constant/4pi) (q(vector v X unit vector r)/r

^{2})

magnetic constant= 4pi x 10

^{-7}(Tesla x meter)/Ampere

## The Attempt at a Solution

The problem here is a curious cross product outcome.

vector v= 4.5 x 10

^{7}j = <0, 4.5 x 10

^{7}, 0>

vector r= <3-0, 4-0, 0-0>= <3,4,0>

magnitude of r= sqrt(3

^{2}+4

^{2})= 5

unit vector r= vector r/ magnitude of vector r= <3,4,0>/5

[itex]\vec{v}[/itex]X[itex]\hat{r}[/itex]= <0, 4.5 x 10

^{7}, 0> X <3, 4, 0> =

((4.5 x 10

^{7}(0) - 0(4))i - (0(0) - 0(3))j + (0(4) - 4.5 x 10

^{7}(3))k)/5 =

(-13.5 x 10

^{7}j)/5= <0, 0, -13.5 x 10

^{7}>/5

Wouldn't that imply that the cross product vector is in the -Z direction? However, using right hand rules, shouldn't the cross product vector be in the positive Z direction?

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