Excuse me, do you know how fast you were going?
TU staff, students measure speed of light with lasers
By Megan Bradshaw on January 15, 2020
Late in 2019, in a small classroom on the fourth floor of Smith Hall, Towson University students got up close and personal with a basic tenet of physics: the speed of light.
“The students in PHYS 242 have spent the semester learning about electric and magnetic fields. Now, they have just learned that these two fields are actually two sides of the same coin—and that the ‘coin’ is light itself,” says James Overduin, an associate professor in the Department of Physics, Astronomy and Geosciences.
During the demonstration, the students split a laser beam into two. One reflected off a mirror to a detector after a short distance. The other passed through the mirror and continued further before reflecting off another mirror toward a second detector. Using the times recorded, the students were able to calculate light’s speed: 670,616,629 miles per hour.
The experiment itself took considerably longer to develop. Research students Jon Perry, Carmen Cuestas and Calin Reamy began in the summer to finetune the procedures and techniques needed to achieve an accurate measurement.
“Jon showed up at all hours to test and improve the apparatus and was never satisfied, always thinking about how we could be more certain of the measurement and its accuracy. Without him, it would not have happened,” stresses Overduin.
The students originally directed the laser 120 meters down the length of Smith Hall’s main hallway. When they continued to be interrupted by foot traffic, the group came in at night to record measurements.
Overduin also credits staff members Jeff Klupt and Jim Selway for their parts in the experiment. Klupt, the department’s electronics shop manager, “rescued” the demonstration, according to Overduin, by building a modulator to replace a malfunctioning measuring component. Overduin describes teacher-in-residence Selway’s energy and enthusiasm as “crucial” to the success of the experiment.
Now was the perfect time for students in PHYS 242 to see the demonstration since the next class in the introductory physics sequence acquaints students with the concepts of waves and relativity.
“I really want students to understand physics,” says Overduin. “Not only in a theoretical way but because they have seen it for themselves. Then all the rest of relativity theory follows, including the conclusion that the past, present and future are all equally real. They don't ‘happen,’ they just ‘are.’ That's the kind of incredible leap that caused me to fall in love with physics and what I hope to share with my students through demonstrations like this.”