Anemometers (pictured) are used to measure wind speeds. The length of each arm,
ID: 1907597 • Letter: A
Question
Anemometers (pictured) are used to measure wind speeds. The length of each arm, as measured from cup to cup, is 43.5 cm. The friction in the bearings is negligible. The idea is to attach a coil of wire of radius 13.2 cm to one of the arms and use the EMF induced by the magnetic field of the Earth to light the bulb.
The bulbs possess 234 ? of internal resistance but need 11.5 W of rms power dissipation to be visible at night. (The resistance of the wire is negligible.) . The magnetic field of the Earth is 0.500 gauss and is oriented roughly horizontal with the Earth, and that 93.5 mph is considered the threshold of dangerous wind speed. Calculate the number of turns in the coil wire needed to light the bulb.
Explanation / Answer
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