For a long straight wire carrying a current I, the magnitude of the magnetic fie

Question

For a long straight wire carrying a current I, the magnitude of the magnetic field, B produced at a perpendicular distance, r from a wire is given by B = Mu_0 I/2 pi r where Mu_0 = 4 pi 10^-7 N/A^2 or (T-m/A) is the magnetic permeability of free space and is a constant. The amount of electric current, I is measured in Amperes (A) and r is measured in m. Thus the circle formed by the distance r from the wire has magnetic field of the same magnitude. However, the direction of the magnetic field at a point on the circle is the tangent at that point. Since there are two possible directions for the tangent, the direction, by convention, is determined by the right hand rule. Study the applet carefully and answer the following questions. The figure above shows a wire perpendicular to the page. The wire carries a current I = 2.7 A flowing into the page. Your first task is to find the direction of the magnetic field at various points at a distance r = 0.15 m from the wire. Use the compass rose for the direction. The direction of the magnetic field at E is along . The direction of the magnetic field at D is along is . The direction of the magnetic field at C is along . The direction of the magnetic field at A is along .

Explanation / Answer

The magnitude of magnetic field B produced at a perpendicular distance r from a wire which is given by,

B = u0 I / 2 (pi) r

B = 4 (pi) x 10-7 m T/A) (2.7 A) / 2 (pi) (0.15 m)

B = 36 x 10-7 T

B = 3.6 x 10-6 T

To find the direction, point a rightt thumb into the page and fingers move in the direction of the field :

1. The direction of the magnetic field at E is along W

2. The direction of the magnetic field at D is along N

3. The direction of the magnetic field at C is along E

4. The direction of the magnetic field at A is along SE

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