Cart Velocity

Velocity laboratory

Objective: To measure the speed of a cart using interferometry and a distance over time method. Do the two methods agree within error?

Model: Velocity is defined as distance travelled divided by the time to move that distance. The distance can be determined from the wavelength of EM radiation traversing an interferometer while the time is that for an interference maximum to go through one cycle. It can also be determined by the distance the object travels in a given time, called the “stopwatch method.”

Method: A microwave EM wave traverses a Michelson interferometer in which one arm moves on an air cart. The interference pattern is recorded on an oscilloscope. The time between maxima is recorded and corresponds to a distance traveled by half a wavelength of that radiation. In the “stopwatch method” the beginning and end of the cart cuts a laser beam to give electrical pulses which, when displayed on a scope, yield the transit time for the distance between the front and back of the cart.

Procedure: The interferometer content needed is described in these links: https://en.wikipedia.org/wiki/Doppler_radar https://en.wikipedia.org/wiki/Doppler_effect For the for the “stopwatch method” the cart breaks a laser beam which illuminates a photodetector. On one channel of the scope you measure this detector's output while on the other channel you measure the microwave detector’s output from the interferometer.

The source emits a harmonic EM wave at 10 GHz by accelerating electrons in an antenna ( like generating waves by accelerating the end of a string up and down).The detector will be studied in another lab. Assume that the detector measures the intensity of the incident wave.

Please include an appendix addressing the following points, which are associated with thinking critically about the lab :

1.) Applying principles: what fundamental principles are associated with the model?

2.) What assumptions did you make in the model?

3.) What assumptions did you make relating to how the apparatus appropriately tests the model?

4.) How do you know that the sources (citations) you used are reliable?

5.) Emphasis on supporting your conclusion with evidence: what type of evidence are you using to draw the conclusion that the data do or do not support the model?

6.) Assessing the impact of additional evidence: what additional ways could you have tested the model?

Method used to measure g:

There is a company in Longmont which makes a product that uses a mirror as one mirror in a Michelson interferometer. The company link is found here (http://www.microglacoste.com/fg5x.php) This mirror moves in free fall and so accelerates. To whom do they sell their product (approx 10^6 dollars)? By using accurate clocks and knowing the wavelength of the source both to 9 significant figures they measure g which is useful to oil companies.