A: Magnets have flux line extending out at the square root of the distance. as a wire cut these lines it set up a current flow by the rule of the thumb
AC: Alternating Current The current oscillates cyclically between a maximum and an minimum. DC: Direct Current This is fixed. The current is always at a constant value.
By way of rectifiers - which are diodes (allow current to flow in one direction only), coupled with other electronics used to smooth the AC wave. A simple design includes a rectifier, a power...