# Angle between B-Field and X-axis

## Homework Statement

Two long horizontal straight parallel wires are 3.18 cm apart and each carries a current of 9.25 A in the directions shown in the above figure. What is the magnitude of the B-field at point P, which is at a perpendicular distance of 2.25 cm from both wires?

## Homework Equations

What is the direction of the B-field at point P? Give the angle between the x-axis and the B-field in degrees (give your answer as an angle between 0 and 359 deg.).

## The Attempt at a Solution

I did part 1, and found the magnitude of the B-field, which is 1.16×10-4 T and is correct, and then I'm stuck on part B, I think according to my image, the x and y components both will double, but it shouldn't affect my angle, but it's wrong. I think my assumption is wrong. Can anyone please help me with the angle?

Thank you very much!

#### Attachments

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## Answers and Replies

supratim1
Gold Member
the y components will cancel out, and the x components will add up. check it by thinking about the tangent to the magnetic field line at P due to each wire.

the y components will cancel out, and the x components will add up. check it by thinking about the tangent to the magnetic field line at P due to each wire.

If my y components cancel out and my x-components add up, then will my angle be 359?

How did you get the magnetic field in part 1?

gneill
Mentor
How did you get the magnetic field in part 1?

What's the magnetic field strength at some distance r from a long, current carrying wire? What's its direction?

I'm stuck on a similar question as well.

My y components cancelled out and the total magnetic field is just 2*the x component of one wire.

Doesn't this mean it has to be in x direction if there's no y component..

It should be 180, but that's wrong and so is 0.

Actually, it's the x components that cancel out, not y, so the angle should be 270?

Last edited:
gneill
Mentor
I'm stuck on a similar question as well.

My y components cancelled out and the total magnetic field is just 2*the x component of one wire.

Doesn't this mean it has to be in x direction if there's no y component..

It should be 180, but that's wrong and so is 0.

Is your question exactly the same or only similar? Current directions matter.

It's slightly different. Currents are in opposite directions. 270 doesn't seem to be correct either though.

gneill
Mentor
It's slightly different. Currents are in opposite directions. 270 doesn't seem to be correct either though.

Well there you go; you'll need to see how that affects the B-field directions.