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 250 turns of fine wire with total resistance 1.5 . The field between the poles of the magnet is 0.35 T ; assume that the field does not extend beyond the edge of the magnet. The coil and the mount that it rides

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

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

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

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

a.Directed up in the "Top view" figure. b.Directed down in the "Top view" figure. c.Directed to the left in the "Top view" figure. d.Directed to the right in the "Top view" figure. Side view Top view

Explanation / Answer

A)From Ohm's law

V = IR => I = V/R

I = 5/1.5 = 3.33 A

Hence, I = 3.33 A

B)since the field will be inwards, the current is clockwise, so the force has to be upwards.

a.Directed up in the "Top view" figure.

C)The magnitude of net force on the coil will be:

F = B I L

F = 0.35 x 3.33 x 0.01m = 0.0117 N

Hence, F = 0.0117 N

D)F = ma

a = F/m

We have calculated the force, but for the calculation of cceleration we need mass of the cooil, which is not provided in the question. Hence information is insufficient for this part.

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