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Unformatted text preview: Solutions for Hand-In Set #4 PHYS 212 - Spring 2007 Problem A21— An electromagnet Tried this out with two batteries in series — it worked very well. I first tried touching the two nails together before applying the current — there was no visible at- traction. With the circuit connected, though, the small nail jumped up to the big one and held tight. When I disconnected the leads, the small nail did not drop off, although the attraction was reduced. There was still some residual magnetism, presumably due to the ferromagnetic behavior of the large nail (hysteresis). The nail becomes a magnet in the first place because the wrapped wire acts as a solenoid. The current going through the wire produces a magnetic field within the solenoid. The nail happened to be within the solenoid, so the magnetic field from the solenoid permeated the nail and magnetized it. Problem A22— Solenoid The approximate magnitude of the magnetic field within a long solenoid having n turns per unit length, each carrying a current...
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