Map sapling earning Investigators are researching the appearance of a strange mo

Question

Map sapling earning 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 117 turns of single-strand copper wire, you use a motor to rotate the coil at a constant angular speed of 70.0 revolutions per second at various orientations and locations throughout the room. In one particularly signficant orientation, you notice a maximum induced voltage of 3.15 V appearing in the coil lf the radius of the coils is 1.00 cm, how strong was the magnetic field that produced this EMF? Number 000194 T Can you rule out the possibility that unusually strong magnetic fields are causing the strange behavior? No, because the magnetic field producing the EMF is much stronger than the magnetic field of the Earth Yes, because the magnetic field producing the EMF is about the same strength as that of the Earth Incorrect Paranormal skeptics use other equipment to investigate claims of ghosts and poltergeists, such as video and audio recorders

Explanation / Answer

Hi,

In this case we simply have to apply the Faraday's Law of Induction to find the magnetic field once we have the area of a coil, turns of it and the angular speed. The general formula to find the induced voltage is:

V = NABsen(t) ; where :

is the angular speed, which is equal to 2*f, where f is the frequency which is measured in revolutions per second

N is the number of turns of the coil

A is the area of the coil which in this case van be calculated as : A = *r2  ; r = radius of the coil

B is the magnetic field

V is the induced voltage

However, as they are giving us the maximum voltage, that means that sen(t) should be equal to one so:

B = V/(NA)

So; A = *r2 = (0.01 m)2 = *10-4 m2 ; and: = 2*f = 2*70 = 140 rad/s; This means that B should be:

B = (3.15 V)/[ (140 1/s)*(*10-4 m2)*(117) ] = 0.195 T

When I think about the result and the two options they are giving you I do think that we can't rule out the possibility of unusually strong magnetic fields in that house, because the magnetic field calculated is almost 2000 times stronger than the magnetic field of the Earth (which is about 1*10-4 T)

I hope it helps.

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