• A Transducer something which changes or transforms one form of energy into another

In Electric Motors: - 

• Electrical energy is transformed into mechanical energy.
• To do this: - Electrical energy is used to induce magnetism. 
• Magnetism uses the forces of repulsion and attraction to cause movement. Like poles repel, opposite poles attract (N S, N N, S S).
• To demonstrate the principles of an electric motor. Mount a horseshoe shaped magnet onto a board in a fixed position, mount a bar magnet onto a small pivot by pinning it to the board as shown in Fig 11

Fig 11

The bar magnet will rotate until its North pole is closest to the South pole of the horseshoe magnet. The bar magnet will not move from this position until the magnetisation of the horseshoe magnet is reversed, To reverse the polarity, the horseshoe magnet is flipped over horizontally, reversing the magnetic poles. The bar magnet rotates through 180^o until its North and South poles are reversed. If the horseshoe magnet is constantly flipped over in this fashion, The bar magnet will constantly rotate to keep up with the changing polarity of the magnetic poles produced by the horseshoe magnet.