# Find the magnetic field at a point

## Homework Statement B=(μ0*I)/(2πr)

## The Attempt at a Solution

B2 = (4*4*10-7)/(2*0.1)
= 8 μT
B1 = (3*4*10-7)/(2*0.1)
= 6μT
Could I know how to determine the directions ?

## Answers and Replies

BvU
Science Advisor
Homework Helper
Know about the right-hand rule ?

The directions matter (to some extent), but
do the signs matter ? They are only asking for a magnitude ...

Know about the right-hand rule ?
Yeah

BvU
Science Advisor
Homework Helper
Yeah
So draw the arrows to find how you have to add them.

So draw the arrows to find how you have to add them.
B2 = 8μT (-j) , because the direction of I2 is (-i).
B1 = 6μT (i) , because the direction of I1 is (j)
So , Bnet = √(82+62) = 10 μT ?

BvU
Science Advisor
Homework Helper
the direction of I2 is (-i)
I'd vote for ##-\hat k## I'd vote for ##-\hat k## So , B2 (##-\hat j##)
B1 (##\hat i##)

BvU
Science Advisor
Homework Helper
I agree. (I also agreed with #5, except for the directions of the currents )

I hope you now understand my frivolous 'do the signs matter': in this case just knowing that the field vectors are perpendicular is enough to get 10 ##\mu##T as answer. Normally the signs certainly do matter.

To boot a small ##\TeX## tip: Donald Knuth has provided \imath and \jmath so the hat and the dot don't pile up: ##\ \hat\imath,\ \hat\jmath ##

• Fatima Hasan