In desert areas of Africa where there is no electricity the Bedouins on camels carry with them colourful boxes of the size of a CD-player equipped with a crank. The crank is difficult to turn, but if you manage to turn it you can listen to the radio for some time. The box contains a generator similar to the one placed in this torch with a push-in handle. If you push it several times a magnet inside starts to rotate and creates electricity in the coil and the bulb glows.

The principle of operation of this torch is the same as in a huge power plant. An external force - a hand, or turbines powered by steam or water moves magnets or a coil and create electricity. This phenomenon is called electromagnetic induction and was discovered by Faraday.

The other torch is not equipped with a crank. Shaking the torch up and down you move a magnet through a coil inside and the bulb glows. (The manufacturer from China fitted the torch with two small batteries just to be sure).

The phenomenon of electromagnetic induction involves generating of electric currents in a circuit, if the magnetic field closed inside this circuit changes. We say that an electromotive force emf is induced and causes the electrical current flow.

This phenomenon was discovered by Michael Faraday (and independently Joseph Henry), inspired by Christian Oersted's who showed that the electric current creates a magnetic field around.

Faraday noticed that the decisive factor for the emf amplitude is the velocity of the magnetic flux Φ_B changes.

and if the circuit contains N N wires it is:

Therefore, moving the lamp up and down faster (or cranking up harder in the other type lamp) creates bigger currents. The number of wires in the induction coil is also important.