Physics 123 Weeks 8 & 9 (Electromagnetic Induction)
**WARNING** Any demos that require a supply can "short out" the power supply easily. Please be aware of your circuits, and include a contact key switch or resistor block when necessary.
Inductance
Assortment of Inductors
These are examples of common household items, all of which use inductors. Please feel free to pass these around to your students.
Back EMF
Although this circuit is powered with a 6V battery you can cause a 90V neon bulb to flash! since there is a large coil in parallel with the bulb, once the circuit is open it will act as a step up transformer.
Induced Currents
A galvanometer is connected to a coiled wire. When a cow magnet is inserted and removed from the coil, and induced current is displayed on the galvanometer.
Color Changing LED
A red and green LED are connected to a coil. When you insert the coil into, or remove it out of, a strong magnetic field, the induced current will light up one of the LEDs depending on its direction.
Creating Currents with Coils
Connect the smaller primary coil to a battery. When you then move that coil into or out of a larger coil an induced current will be displayed on the galvanometer.
**Please remember to disconnect or the battery will die**
Eddy Currents
Eddy Current Pendula
Two aluminum sheets with different shapes are allowed to swing through a strong magnetic field. The induced eddy currents will have a noticeable and dramatic affect on one of your pendula!
Eddy Current Tubes
After dropping a non magnetic item down the tube, drop the accompanying neodymium magnet! The induced eddy currents will significantly decrease the acceleration, and you will appear to have defied gravity!
Feeling Eddy Currents
Allow your students to drag a strong magnet across this large copper plate. They will feel a noticeable resistance created from the induced Eddy currents. You could also lay the magnet on the sheet next to a non magnetic item and slowly create an incline.
Fling the Ring
Use the Elihu Thompson apparatus (with and without the iron core) to induce a current in various ring like objects. Depending on whether or not the ring has a gap in it, the Eddy current will shoot the ring upwards.
Generators and Motors
Simple Motor
A current carrying wire is looped and suspended over a magnet. When connected to a battery and given a slight push, the coil will begin to spin and you have a simple motor! **You are shorting the battery, so do not leave it connected**
Hand Crank Generators
Show your students how mechanical energy can be transformed into electrical energy, or vice versa, by using these small generators. Use with a light bulb to simulate an electrical generator, or a capacitor to simulate an electric motor. You can even hook two together!
DC and AC Generators
Use the hand crank to rotate the wire coil in the magnetic field. Depending on how your galvanometer input is configured, an AC or DC current will be displayed.
Electromagnetic Motor
This apparatus is a perfect demonstration to show your students how an electromagnetic motor works!
**Caution** It can rotate quite rapidly so please start with 6V, and slowly increase to desired voltage while not exceeding 15V.