Investigators are researching the appearance of a strange movement of objects in

Question

Investigators are researching the appearance of a strange movement of objects in what the local community considers a haunted house. The owners of the house attribute the cause to poltergeists; others blame overly strong magnetic fields could be the cause. As a scientific investigator of paranormal claims, you decide to investigate. You will start by focusing on magnetic fields.* Using a coil made of 321 turns of single-strand copper wire, you use a motor to rotate the coil at a constant angular speed of 50.0 revolutions per second at various orientations and locations throughout the room. In one particularly signficant orientation, you notice a maximum induced voltage of 1.15 V appearing in the coil. If the radius of the coils is 1.00 cm, how strong was the magnetic field that produced this EMF?

Explanation / Answer

Voltage is expressed as follows:

V = N*d(B*A*cos(wt))/dt = - N*B*A*w*sin wt

The magnitude of maximum voltage occurs at sin wt =1, so the maximum voltage is,

Vmax =  N*B*A*w

1.15 = 321*B*[pi*0.01^2]*[50*2*pi rad/s]

Therefore, the magnetic field is,

B = 0.036 T

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