The tolerance is +/-2% Chapter 32, Problem 048 Suppose that the dipole moment as

Question

The tolerance is +/-2%

Chapter 32, Problem 048 Suppose that the dipole moment associated with an iron atom of an iron bar is 2.4 x 10-23 j/T. Assume that all the atoms in the bar, which is 5.2 cm long and has a cross-sectional area of 1.3 cm2, have their dipole moments aligned. (a) What is the dipole moment of the bar? (b) What torque must be exerted to hold this magnet perpendicular to an external field of 2.2 T? (The density of iron is 7.9 g/cm3 and its molar mass is 55.9 g/mol.) (a) Number Units (b) Number Units

Explanation / Answer

a) dipole moment = 2.4 * 10-23 J/T

L = 0.052 m, A = 1.3 * 10-4 m2

number of atoms N = (7.9 * 5.2 * 1.3 * 6.022 * 1023) / (55.9)

= 5.75 * 1023 atoms

dipole moment of the bar = 2.4 * 10-23 J/T * N

= 2.4 * 10-23 * 5.75 * 1023

= 13.81 A.m2

b) Torque = mu B sin 90

= 13.81 * 2.2 * sin 90

= 30.4 N.m

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