6A01.10 - Speed of Light
To measure the speed of light.
Gather a two channel oscilloscope, two bnc to alligator oscilloscope probes, and speed of light circuit board with accompanying fiber optic cables and dc power plug. Plug the oscilloscope into the wall and connect the probes to channels 1 and 2. Connect probe for channel one to the reference and ground connections on the circuit board. Connect the probe for channel 2 to the delay and ground connections on the circuit board. Plug dc power into the circuit board and cart. Turn the calibration knob on the circuit board to 12 o'clock.
Insert one end of the 15cm fiber optic cable into the blue LED port. make sure signal has good curvature and not oversaturated. plug the second end into the black LED port. Make sure the oscilloscope reads a signel from channel 2. A reference signal will also be shown on the oscilloscope. adjust the calibration knob until the signals amplitude's overlap. y-axis should be 1V/div, and x-axis 50ns/div. remove 15cm cable and be careful not to change anything. Insert one end of the 20m fiber optic into the blue LED port. Insert the other end into the black LED port. The signal from the 20m cable should be about 100ns to the right of the previous signal's position which is marked by the reference pulse. measure the distance on the x-axis in nanoseconds. It should be about 100ns. To calculate the speed of light use the equation c = n*l/t , where n is the index of refraction of the fiber optic and is 1.5. L is the length of the cable at 20m, and time is the distance between peaks on the x-axis and should be around 100ns. c = 300,000,000 m/s.