Question

A flashlight can be made that is powered by the induced current from a magnet moving through a coil of wire. The coil and magnet are inside a plastic tube that can be shaken causing the magnet to move back and forth through the coil. Assume the magnet has a maximum field strength of 0.05 T. Assume that the radius of the coil is 1.5 cm and the magnet is shaken with a frequency of about two shakes per second. Specify the the number of turns necessary to light a standard 1-watt, 3-V flashlight bulb.

Answer 1

here,

the magnitude of field , B = 0.05 T

radius of coil , r = 1.5 cm = 0.015 m

freqeuncy of oscillation , f = 2 shakes /s = 2 Hz

let the number of turns be N

the induced emf = 2 *pi * f * N * Area * B

3 = 2 *pi * 2 * N * pi * 0.015^2 * 0.05

solving for N

N = 6762 turns

the required number of turns are 6762 turns