28. Magnetic Fields and Forces

A rectangular loop of wire carries a 2.0-A dc current and lies in a plane which also contains a very long straight wire carrying a 10.0-A current as shown in Fig. 28–58. Determine (a) the net force and (b) the net torque on the loop due to the straight wire.

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(II) An iron atom has a magnetic dipole moment of about 1.8 x 10⁻²³ A • m² . (a) Determine the dipole moment of an iron bar 15 cm long, 1.2 cm wide, and 1.0 cm thick, if it is 100 percent saturated. (b) What torque would be exerted on this bar when placed in a 0.80-T field acting at right angles to the bar?

(I) If the current to an electric motor drops by 18%, by what factor does the output torque change?