## magnetic fields

A Fe+ ion is traveling at 200 m/sec in a direction 20 deg south of west at a point. The magnetic field at that point is 0.4 T directed at 10 deg west of south. What is the instantaneous magnetic force that acts on the Fe is how many newtons?
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 The magnetic force on a charge that travels through a magnetic field is: $$\vec F_m = q\vec V \times \vec B = q|V||B|\sin \alpha$$ ([itex]\alpha[/tex] being the angle between the field vector and the velocity vector of course.)

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 Originally posted by Chen The magnetic force on a charge that travels through a magnetic field is: $$\vec F_m = q\vec B \times \vec V = q|B||V|\sin \alpha$$ ([itex]\alpha[/tex] being the angle between the field vector and the velocity vector of course.)
I normally would not be picky on such things. However, it should be corrected that the general form of Lorentz force for the magnetic field term is proportional to q(v x B), not q(B x v).

Since the original question involves the exact vectorial direction of the force, and since cross products are not commutative, this can produce an error in the direction.

Zz.

## magnetic fields

Of course, I've corrected my post. Thanks for pointing my mistake out. [:)] Usually I just use the right-hand rule to find the direction of the magnetic force.