Question

1. You have a hand crank flashlight in your car for emergency purposes. The flashlight works by turning a bunch of coils of wire (let’s say 500 of them) in a permanent magnetic field (of 0.2T). The coils are circular with a radius of 1cm. Unfortunately, you find yourself in the dark looking for something you dropped on the ground. If the flashlight needs a peak current of 50mA to turn on and it has a resistance of 5 ohms, how fast do you have to turn the handle to get it to turn on? You are looking for an angular frequency here. Convert to revolutions per second to see if your answer is reasonable for turning the crank.

Answer 1