Calculate the force on a particle from magnetic field of infinite wire

[eviljay]

Homework Statement

Problem: Determine an expression for the magnitude of the magnetic force on a charged particle moving near an infinitely long wire, carrying a current i.

• Particle with charge q
• Magnitude of the particles velocity = |v|
• Magnetic field strength = B
• Current = i

Homework Equations

B can be calculated with:
B=\frac{μ_{0}i}{2\pi{r}}

Magnitude of force can be calculated with:
F=q*v*b*sin(θ) (Cross product of the particles velocity vector and the magnetic field vector)

The Attempt at a Solution

I've combined these equations to come up with a single equation for the magnitude of the force on the particle:

F=\frac{q*v*μ_{0}*i*sin(θ)}{2\pi{r}}

However this final equation is the part I am not confident on. I've proceeded on the basis the the magnetic field around an infinite wire carrying current is non-uniform; that is the direction of the magnetic field is not constant, but would appreciate my working being checked!

Thanks in advance!

 

[mfb]

The magnetic field is not constant, this will change sin(θ) and r in a trajectory. But the equation for the force at a specific radius with a specific angle is correct.
Current is written with a capital I. "i" is usually the imaginary unit.

 

[rude man]

Looks good.

BTW i = √(-1) is only for physicists.

Real men (engineers) use j = √(-1) and i is very regularly used to denote current

 

[mfb]

Physics Forums > Science Education > Homework & Coursework Questions > Introductory Physics >

BTW i = √(-1) is only for physicists.

And mathematics as well.

 

[rude man]

And mathematics as well.

Yeah, but not real men (and women)!

 

[eviljay]

Thanks both! Just needed that extra pair of eyes to look at it