Yesterday during the tsunami warning my parents found our hand-cranked radio that could run without electricity or batteries. But what really makes this radio run? Physics, of course! Recently we have been studying electromagnetism and so now I can explain how something can have power with no power source. Inside this radio (I'm assuming) there is a coil of wire attached to the radio. This wire will act as a generator and the person turning the crank will supply the necessary energy. As the mechanism is cranked energy is supplied and the small wire moves in a magnetic field. Because this wire moves in a magnetic field an emf is induced and thus a current is created. Since power equals current times voltage, the radio has power and can turn on. The power can be stronger due to more loops in the wire, turning the crank faster (greater angular velocity), a greater area within the wire, and more time. Conservation of energy applies here but some energy is lost to heat.
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