12 Investigators are researching the appearance of a strange

12

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 60.0 revolutions per second at various orientations and locations throughout the room. In one particularly signflcant orientation, you notice a maximum induced voltage of 2.15 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? 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.* Paranormal skeptics use other equipment to investigate claims of ghosts and poltergeists, such as video and audio recorders.

Solution

For a magnetic field B, if a coil is moved in it the angular velocity of rad/s, has N turns and area is A, then we have:

Maximum e.m.f (E_o) = BAN

Now, as we already have the value for the maximum emf observed in the given the situation, we will form an equation with the above expression to determine the value of B.

Hence, 2.15 = Br^2 N

or, 2.15 = B(3.14) x 10^-4 x 321 x 60 x 2 x 3.14

or, B = 0.05661 = 56.61 microTeslas

Now we know that the earth\'s magnetic field varies from 25 to 65 microTeslas. Therefore we can say that there is not unusual magnetic field present in the house.