Measuring the speed of light these days is a simple college laboratory with the help of an oscilloscope. An oscilloscope can take data at a rate of hundreds millions of frames per second. Here is how we do it. The laser sends a signal to the receiver at point b. But the same signal is sent to a mirror and reflected back to the receiver. And this takes a certain amount of time. The signals are sent to an oscilloscope and the scope reads the delay. I’ve already measured the distance to the mirror and its 30 feet away, 30 here and 30 feet reflected back. The laser sends a signal to the mirror which is reflected back to the receiver. after some time delay. That signal is then sent to the scope. ouch. In order to set a time equal to 0 we’re reflecting the laser signal immediately to the receiver. Now that we’re all set up I’m sending the laser beam to the mirror and back. A delay in rise time is visible on the scope. The data from the scope shows a time delay of 60 nano seconds. Thats 10 to the negative 9 seconds. But he distance we measured was 30 plus 30 feet.
That is 60 feet. 60 feet distance. In a time of 60 nano seconds. That makes the speed of light c = 60 feet per 60 nano seconds about 1 foot per nanosecond. And that amount is what is what Physicists usually refer to the speed of light as, a common measurement. Almost exactly equal to 3 times 10 to the eighth meters per second..