electric generator
A generator turns motion into electricity. Spin a coil of wire in a magnetic field — driven by wind, falling water, hot steam, or a hand crank — and current comes out. It is simply an electric motor run backwards. It answers a very practical question: how is nearly all of our electricity actually made?
Precisely, a generator rotates a coil of area A and N turns at angular frequency omega inside a magnetic field B. The flux through the coil is Phi = B A cos(omega t), so by Faraday's law the induced EMF is EMF = N B A omega sin(omega t). The output is a sine wave that peaks at EMF_max = N B A omega — this back-and-forth voltage is alternating current. Spin it faster and both the peak voltage and the frequency rise.
Power stations are giant generators: the energy source, whether coal, gas, nuclear, or hydro, does nothing more glamorous than spin the coil; the electricity itself comes from Faraday's law. The honest point is that a generator does not create energy — it converts mechanical work into electrical energy, and by Lenz's law the more current the load draws, the harder the coil is to turn.
A hand-crank flashlight spins a magnet past a coil, inducing an EMF that lights the bulb. Stop cranking and it goes dark at once — there is no stored energy, just live conversion of your effort into light.
Cranking spins the coil; Faraday's law lights the bulb.
A generator and a motor are the same machine: supply current and it spins (motor); spin it and it supplies current (generator). This two-way trick is how electric cars recover energy when braking.