Extra credit may be trivial to the overall grade.

In my electronics lab, it sparked an interest in a simple circuit. The task was to build a simple circuit as introduction to how switches worked. The switch would turn on a motor, making it spin forward or backward depending on which direction was desired. After giving the assignment, I mentioned that there would be extra credit worth 5 points if they could put a light emitting diode (LED) into the circuit to show which direction the motor was spinning. The desire for the 5 points of extra credit resulted in a lot of work done in the lab. Typically, many of the students will depart or go on break when they finish the lab assignment. Today, 14 of 16 students stayed until the end of the class to investigate how to add the optional light-emitting diode to the circuit. It caused them to question each branch of the circuit, and which branch would have electricity when the motor ran forward but not backward. They found that the LEDs themselves would stop current if inserted backward. This small optional assignment inadvertently flipped a classroom when the intention was for the student to research online, turn the page in the textbook, or look over and see what the person next to them was doing. Trial and error would have worked too, as there were only a dozen or so ways to put the LED into the small circuit. The trial and error option is slightly more entertaining, as the inexpensive LEDs will burn out if connected incorrectly, but give a pretty flash of light when they die. The extra credit, given the vast amount of points available in the course, will likely not change the final grade, but it made the lab special for today. It was the extra sprinkles on the chocolate frosted glazed donut, the third peanut in the shell, or the one extra chocolate chip in the cookie carefully selected from the fresh batch. Unneeded, but when it is discovered, results in the experience being even better.