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 240 turns of fine wire with total resistance 1.6? . The field between the poles of the magnet is 0.35T ; 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 13g .

1) If a voltage of 5.0 V is applied to the coil, what is the current?

2) If the current is clockwise viewed from above, what is the direction of the net force on the coil?

3) What is the magnitude of the net force on the coil?

4) What is the magnitude of the acceleration of the coil?

Explanation / Answer

Given that the magnitude of magnetic field is B = 0.35 T

Number of turns in the coil is N = 240

Resistance of wire is R = 1.6 ?

Length of the square is L = 1.0 cm = 0.01 m

Total mass of coil is m = 13 g = 0.013 kg

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The current in the coil is I = 5.0V / R

                                       = 3.125 A     

Magnetic force on the coil is F = NBIL sin?

                                               = 240*0.35T*3.125A*0.01m*sin90o

                                               = 2.625 N

Directed to the right

The acceleration of the coil is a = F /m

                                               = 2.625 N / 0.013 kg

                                               = 201.92 m/s2

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