Magnetic information on hard drives is accessed by a read head that must move ra

Question

Magnetic information on hard drives is accessed by a read head that must move rapidly back and forth across the disk. The force to move the head is generally created with a voice coil actuator, a flat coil of fine wire that moves between the poles of a strong magnet, as in the figure. Assume that the coil is a square 1.0 cm on a side made of 150 turns of fine wire with total resistance 1.7 omega. The field between the poles of the magnet is 0.33 T; assume that the field does not extend beyond the edge of the magnet. The coil and the mount that it rides on have a total mass of 15 g. C) What is the magnitude of the net force on the coil? D) What is the magnitude of the acceleration of the coil?

Explanation / Answer

Given that the magnitude of magnetic field is B = 0.33 T Number of turns in the coil is N = 150 Resistance of wire is R = 1.7 Length of the square is L = 1.0 cm = 0.01 m Total mass of coil is m = 15 g = 0.015 kg ------------------------------------------------------- The current in the coil is I = 5.0V / R                                        = 2.94 A      Magnetic force on the coil is F = NBIL sin                                                = 150*0.33T*2.94A*0.01m*sin90o                                                = 1.455 N The direction of force is into the page. The acceleration of the coil is a = F /m                                                = 1.455 N / 0.015 kg                                                = 97.02 m/s2                                                = 1.455 N The direction of force is into the page. The acceleration of the coil is a = F /m                                                = 1.455 N / 0.015 kg                                                = 97.02 m/s2

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