After making an improvised coil (experiment 25) and cutting a coil out of a speaker (experiment 27) in this experiment the self-inductance of a coil is demonstrated. As a coil in this experiment I used 44 meters of coated copper wire on a spool. In parallel with the coil two low current LED’s are connected. The polarity of one LED is opposite to the other. In the Make: Electronics book a 220 ohm (rated 0.25 watt or higher) resistor is used. Instead I used to two 470 ohm resistors in parallel (this totals to 235 ohm resistance) to protect to resistors and more important my breadboard.
After pressing the button (without releasing it) one LED lights up briefly. Releasing the button prompts the other LED to lights up briefly. This experiment demonstrates that the coil opposes any change in current first by blocking the current and forcing the current to pass through the first LED and then, when the button is released, by releasing it’s stored energy over the second LED.
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| All components on the breadboard. Two 470 ohm resistors in parallel were used to counter for the 1/8 watt resistors that I use. |
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| Experiment in progress. On the right the 44mm copper coated coil. |