Transcript Slide 1
ELECTRIC MOTORS SPH4C Electromagnetism: More Practice Electromagnetism: More Practice The motor principle A device that uses an electromagnet in a permanent magnetic field to apply a directed force is called an electric motor . It operates by the motor principle. The motor principle A device that uses an electromagnet in a permanent magnetic field to apply a directed force is called an electric motor . It operates by the motor principle (aka RHR#3). The Motor Principle (aka RHR#3) Two magnetic fields interact with each other to produce a force, so a conductor that carries current through an existing magnetic field experiences a force perpendicular to both the current and the external magnetic field. RHR#3 The direction of the force can be determined by the third right hand rule. Electric Motors The electric motor directs electric force full circle, without stopping part way. In a DC motor, the electromagnet has to change its polarity once every rotation. This polarity change is made because a split ring commutator reverses the current flow in the rotating armature. The Simple Induction AC Motor The direction of AC alternates back and forth anyway. (In North America, this cycles 60 times per second . . . which translates to rps of the motor.) Building a basic DC motor Starting about 3 inches from the end of the wire, wrap it about seven times around the D-cell battery. Remove the battery and cut the wire, leaving a 3 inch tail opposite the original starting point. Building a basic DC motor Wrap the two tails around the coil so that the coil is held together and the two tails extend perpendicular to the coil. Note: Be sure to center the two tails on either side of the coil. Balance is important. You might need to put a drop of glue where the tail meets the coil to prevent slipping Building a basic DC motor On one tail, use fine sandpaper to completely remove the insulation from the wire. Leave about 1/4" of insulation on the end and where the wire meets to coil. On the other tail, lay the coil down flat and lightly sand off the insulation from the top half of the wire only. Again, leave 1/4" of full insulation on the end and where the wire meets the coil. Building a basic DC motor Place the coil in the cradle. You may have to give it a gentle push to get it started, but it should begin to spin. If it doesn't spin, check to make sure that all of the insulation has been removed from the wire ends. If it spins erratically, make sure that the tails on the coil are centered on the sides of the coil. Building a basic DC motor http://www.youtube.com/watch?feature=player_emb edded&v=P6lBvAQ9P_c