#### physicsbhelp

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

a) What is the direction of the net magnetic filed 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 10^6 meters/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 0.

2. The attempt at a solution

I know the answer to part b). it is 6e-6 T and 4e-7 T.

i need help with the other parts. i think, for part a), the direction of the net magnetic field is in the -x becuase the direction of the magnetic filed for the 3Amp wire is +z and the direction of the 1A wire is -z but i need help!!!

THE PICTURE IS ATTACHED.!!!!.!!!!!!!!!!!!!!!!!!!!!!!!!

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#### jcpwn2004

can't really help until the picture is approved lol. You should jus take a screen shot of the problem and upload the pic to imageshack or something.

#### physicsbhelp

do you know who approves the pictures? can someone please tell them to approve the picture???

#### physicsbhelp

i drew the picture.
so does that mean that no one can see the picture?

well i can give you a general description it is like the x and y-axis but is is slanted, although the angles are 90 degrees.
there is a line going to the x-axis and a line going to the y-axis from point P so basically it looks like a rectangle on top of a almost completely turned x and y-axis. the 3A is on the y-axis and the 1 A is on teh x-axis. the 1.0m line goes from point P to the y-axis and the 0.5m line goes from point P to the x-axis.

#### pinkenergy

i wanna help, but i cant quite understand your description. post it to photobucket and host from there.

#### pinkenergy

no problem. i think everyone was just waiting for you to post an image, people totally wanna help so no dont worry. :)

#### pinkenergy

omg, dont kill me, but i dont get it. i know someone will though.
to verify, the velocity is pointing north, the magnetic Force is pointing left... the magnetic field for the 3Amp wire is +z, and magnetic field for the 1Amp wire is -z.......?

#### pinkenergy

oh, but for part d...
F = q v B sin (theta)
rearrange for q, because you have F and v, and you, yourself found B :)

after you find q, you can do part e...
E = F/q

#### physicsbhelp

wait, what is the value of sin theda????? and what is B?

#### physicsbhelp

IS theda 90 degrees?
and i still don't know what B is?
HELP!

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#### pinkenergy

i totally cant even answer you on theta bc the diagram seems to be missing B fields.
B = magnetic field.

all i know is F = 0 when charges move parallel or antiparallel to the magnetic field bc sin0 = 0 and sin180 = 0

i hope someone helps...ill keep checking on this because i want to know the answer too. ps. have you tried posting on answers.yahoo?

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#### alphysicist

Homework Helper
Hi physicsbhelp,

About your answers to part b: they want to know the net magnetic field force that comes from adding the separate magnetic field produced by each wire at point P. Those numbers that you stated, how did you get those? If those were the magnetic fields of the wires then I believe one of them is wrong.

#### alphysicist

Homework Helper
Hi physicsbhelp,

As I said in my last post, I think a good place to start would be with the two numbers you gave to part b. Did you find them using

$$B = \frac{\mu_0 I}{2 \pi r}$$

If so, I believe you made a calculation error in one of them. Once you have the correct magnitudes of each magnetic field, you'll then need to find the direction of each which will show you how to add them together. The vector sum of those fields will be the answers to a and b.

#### Kurdt

Staff Emeritus
Gold Member
Someone has already given the formula for the magnitude of magnetic field due to an infinite wire carrying a current. Do you know of a method to find the direction of a magnetic field around a current carrying wire?

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