Question

You are doing a study of bird migration and need to determine the strength and direction of the Farth's magnetic field B using a magnetometer (a device for measuring magnetic fields). This magnetometer consists of a long wire carrying 10.0 A of current. Assume the wire and the magnetic field are both parallel to the ground. For the two orientations of the wire shown (viewed from above), the magnitude of the force per unit length F/L is given. The orientation of the wire in Figure 1 is perpendicular to the orientation of the wire in Figure II NI FL=0.0 N/cm F/L=5.00 ul/cm (II) a. (4 points) Draw an arrow that indicates the direction of B (when still viewed from above). Please place a box around your arrow so I can clearly identify your answer. b. (12 points) What is the strength of the Earth's magnetic field (in T')? c. (12 points) Your research student is standing 5.00 m away from the wire. What is the strength of the magnetic field at that location due solely to the wire? d. (6 points) The research student in part (c) has a compass needle that aligns itself to be parallel with magnetic field lines. Will the compass needle be deflected to point toward the wire, away from the wire, or neither? Explain your answer.

Answer 1

1.

a)

B I F/L=0.0 N/cm F/L=5.00 pT/cm

b)

magnetic force is given as

F = I B L Sin$\theta$

For figure 1

$\theta$ = 90 and F/L = 5 $\mu$T/cm = 5 x 10^-6 T/((0.01) m) = 5 x 10^-4 T/m

F/L = I B Sin90

5 x 10^-4 = (10) B

B = 5 x 10^-5 T

B = 50 $\mu$T

c)

r = distance of the student = 5 m

B' = strength of magnetic field at the location of student

strength of magnetic field at the location of student is given as

B' = ($\mu_{o}$/4$\pi$) (2I/r)

B' = (10^-7) (2(10)/5)

B' = 4 x 10^-7 T

d)

the needle with deflect in the direction of external magnetic field which is going towards left as seen from above. hence the the needle deflects left.