Magnetic field and currents problem

[waterbottle12]

Homework Statement

8) A long straight horizontal wire is oriented along the north-south direction. Conventional
current flows through the wire from south to north.
a) What is the direction of the magnetic field at a point 5.0 cm above the wire?
b) A compass placed 5.0 cm above the wire points at a 14º angle from north. Assuming that
the Earth's magnetic field points due north, and that the horizontal component of the Earth's field
has a magnitude of 4.0 × 10-5 T, what is the magnitude of the field due to the wire?
c) What is the current in the wire?

Homework Equations

The Attempt at a Solution

a. well since the conventional current is down...I put my thumb down and by RHR, the magnetic field would be clockwise..but I'm not sure what would be the case above the current...

b. Are we finding a magnetic field that when combined with the horizontal component has a direction of 14 from North? o.o

c. At first I thought it was B = (u x I) / 2 x pi x r where u is the permeability of free space consant...but then I saw that r isn't given :/ so now I am confused

 

[Zacku]

Hi,

a. Maybe you should give the answer in term of East, West, South and North direction don't you think?

b. Magnetic field have to be added so if you know the direction of the field generated by the wire you just need to add to it the magnetic field from the earth. The final result is what is measured by the compass. Normally, using simple vectorial analysis you can get the result.

c. Isn't the distance r you are looking for just the 5 cm distance from the wire?