# Electromagnetism question

1. Apr 13, 2010

### sherminator

1. The problem statement, all variables and given/known data

The magnitude of the magnetic field in teslas at a distance d from a long straight wire carrying a current I is given by the relation B = 2 X 10 7 I/d. The two long straight wires shown above are perpendicular, insulated from each other, and small enough so that they may be considered to be in the same plane. The wires are not free to move. Point P, in the same plane as the wires, is 0.5 meter from the wire carrying a current of 1 ampere and is 1.0 meter from the wire carrying a current of 3 amperes.
a. What is the direction of the net magnetic field at P due to the currents?
b. Determine the magnitude of the net magnetic field at P due to the currents.

A charged particle at point P that is instantaneously moving with a velocity of 106 meters per second toward the top of the page experiences a force of 10 7 newtons to the left due to the two currents.
c. State whether the charge on the particle is positive or negative.
d. Determine the magnitude of the charge on the particle.
e. Determine the magnitude and direction of an electric field also at point P that would make the net force on this moving charge equal to zero.

the picture is here

2. Relevant equations
B=uoI/2pir
F=ILB
F=qvB
F=qE

3. The attempt at a solution

a) out, because the 3A wire has a stronger force, and I used RHR
b) B=uoI/2pir, subtracted the two B's, and got 2 X 10^-7 T
c) negative b/c of RHR
d) F=qvB=ILB; qv=IL;q=IL/V. not sure what to do from here
e)F=qE=qvB;E=vB=.2N/C

I'm not 100% confident for any of these, so if someone could just confirm/correct these answers, with explanations if wrong, that would be greatly appreciated.

Last edited: Apr 13, 2010