In Procedure 1: a wire of length L = 3.91 cm sits on an electronic scale. There

Question

In Procedure 1: a wire of length L = 3.91 cm sits on an electronic scale. There is also a uniform mangetic field perpendicular to the wire, and along its entire length. When there is no current in the wire, the scale reads 573 g. When a current I = 48.2 mA goes through the wire, and the scale reads 544 g.
NOTE: Beware of units!

a) Find F, the magnitude of the force on the wire created by the interaction of the current and the magnetic field.
____ N

b) Find B, the magnitude of the magnetic field around the wire.
_________T

c) Suppose the direction of the magnetic field is reversed. What would the scale read now?
___________ g

d) Suppose the system could take large currents. To what would you have to raise the current (before you reversed the direction of B) so the force on the wire entirely supported the weight of the wire (and the scale reads zero)?
_________A

Explanation / Answer

Given that the length of wire is L = 3.91 cm = 3.91x10-2 m Initial masss of wire is m1 = 573 g = 0.573 kg final masss of wire is m2 = 544 g = 0.544 kg ----------------------------------------------------- (a) Force on the wire created by the current and magetic field is              m1g -F = m2g              F = m1*g - m2*g                 = 0.2842 N (b) Magnitude of magnetic field around the wire is            B = F / IL                = 0.2842N / (48.2x10-3A)(3.91x10-2 m)                   = 150.8 T (c)If the current direction is reversed,         new reading is = 573g + 0.2842N / 9.8m/s2                               = 602 g (d) If scale reading is zero, then              BIL = m1*g                 I = m1*g / BL                   = 0.952 A     

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