In-Lab Worksheet, Properties of LightPS253-Physics Lab for Engineers
In-Lab Worksheet, Properties of LightPS253-Physics Lab for Engineers
Name:
**Do not forget to hand this in before leaving class!
Speed of Light, Fiber Optics
Long Fiber Optic Length: 20.01± 0.05m Short Fiber Optic Length: 0.135m± 0.001m
Using the short fiber optic cable, record the O-scope display of the time between consecutive transmitted pulses (Δt value). This should be between 0.5-1.5μs.
Calculate the pulse frequency of the LED transmitter circuit from your information in (1). Remember this is too fast for your eye to see the individual pulses!
Using the cursors on the oscilloscope record the instrument time for each fiber.
tshort cable = 520ns ± 40ns tlong cable = 640ns ± 40ns
Subtract the time found in the short fiber test from the long fiber test, to find the actual time of flight of the photons Δt. This corrects for unknown circuit time delays.
Subtract the short fiber length from the long fiber length to find an effective length l. Remember the Δt from (4) applies to a cable equal in length to the difference of the long and short cables.
Compute the critical angle (θc) for the optical fiber.
What happens to any light in the fiber that is travelling at an angle less than the critical angle?
What happens to any light in the fiber that is travelling at an angle greater than the critical angle?
Compute the longest optical path length Δxlongest path for the light travelling through the fiber at θc.
Compute the average optical path length for any light traveling through the entire fiber.
What is the average velocity of light inside the fiber optic cable?
From your results, determine an experimental value for the speed of light in a vacuum, c.
Given a precisely known reference value for c of 2.99792x108m/s, compute a percentage difference between your experimental value and the reference value.
Also, compute just the discrepancy: . This will indicate to what order you obtained an accurate result. For example, are you accurate to 1 part per thousand (0.001), or 1 part per hundred (0.01), etc.
The speed of light is a very large number ~108m/s, and the timings involved in this experiment were very small numbers ~10-8s. However, you most likely obtained a very reasonable result considering the mathematics and physics concepts involved were relatively simplistic and straight forward. Reflect on the significance of this feat for a few moments and write your thoughts below.
Consider all the materials used: two lengths of fiber optic cable, two electronic circuits, a digital oscilloscope, oscilloscope probes, the LED, the photodiode, a ruler to measure length of the short cable, values given to you.
What do you think would be the most significant known unknowns affecting your result? These would be uncertainties you already know exist and that you know a value for or could reliably estimate a value for.
What do you think could be some unknown unknowns affecting your result? These would be uncertainties you didn’t know or realize existed before running the experiment and obtaining your results, or that you would not know how to estimate.
Out of the unknown unknowns that you’ve contemplated (realizing you know of their existence now) which do you think could be the most significant one impacting your result?
– Page 3 of 3 –
– Page 1 of 3 –
The post In-Lab Worksheet, Properties of LightPS253-Physics Lab for Engineers In-Lab Worksheet, Properties of appeared first on PapersSpot.
