29. Sources of Magnetic Field

(I) Jumper cables used to start a stalled vehicle often carry a 65-A current. How strong is the magnetic field 5.0 cm from one cable? Compare to the Earth’s magnetic field . (5.0 x 10⁻⁵ T) .

A continuous straight stream of protons passes a given point in space at a rate of 2.5 x 10⁹ protons/s. What magnetic field do they produce 1.8 m from the beam?

(I) Determine the magnitude and direction of the force between two long parallel wires 35 m long and 4.0 cm apart, each carrying 35 A in the same direction.

(II) A dc power line carries a current of 85 A west along the tops of 8.5-m-high poles. (a) What is the magnitude and direction of the magnetic field produced by this wire at the ground directly below? How does this compare with the Earth’s field of about ½G ? (b) Where would the current’s magnetic field cancel the Earth’s field?

(II) Two long straight wires each carry a dc current I out of the page toward the viewer, Fig. 28–38. Indicate, with appropriate arrows, the direction of B (→ above B) at each of the points 1 to 6 in the plane of the page. State if the field is zero at any of the points.

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Two long straight aluminum wires, each of diameter 0.42 mm, carry the same current but in opposite directions. They are suspended by 0.50-m-long strings as shown in Fig. 28–66. If the suspension strings make an angle of 3.0° with the vertical and are hanging freely, what is the current in the wires?

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(II) In Fig. 28–36, a long straight wire carries current I out of the page toward you. Indicate, with appropriate arrows, the direction and (relative) magnitude of B (→ above B) at each of the points C, D, and E in the plane of the page.

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