1. The problem statement, all variables and given/known data Have been given the task of creating a circuit powered by a rotating magnet in a copper coil that will charge a capacitor long enough to light an LED for 600 seconds after the rotating magnet has stopped. In all the magnet charge up torches I've opened, there are two 3V Lithium Cells (CR 2032) between the generator and the circuit. These cells aren't rechargable. The current from the generator is AC. I know this shouldn't be too difficult, but can't figure out how to approach it with so many unknown variables. Just looking for any help possible for value of capacitor or resistor. Voltage for LED = 1.5V Power for LED = 4mW Current for LED = 2.7mA t for capacitance discharge = 600s 2. Relevant equations EMF = N(dФB)/dt P = IV C = Q/V I = Q/t F = (A.s)/V 3. The attempt at a solution I know that in Faraday's Law of Induction, the magnetic flux in Webers is defined by the equation. But what does the change in time represent? What time is it referring too in the process of passing the magnet through a single loop? I've entered the values into the capacitance equation and come out with 1.08F. However all capacitors I've found are measured in pF. Any help at all will be much appreciated.