wk3-lab Alex Lei Claudia Nguyen and Grace Amour

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100

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Electrical Engineering

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Dec 6, 2023

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Week 3 Lab Report – Reflection Date: 7/19/2023 Section: A3 Lab Partners: 1. Alex Lei 2. Grace Amour 3. Claudia Nguyen 3.3.2 Specular Reflection (Total Points: 20) Goal: Verify Eq. 3.1 ( θ mirror = ½ θ bench or equivalently θ i = θ r ) for specular reflection. ** θ bench and θ mirror are defined in Fig. 3.7. Schematic Diagram (2 points) : 1

Background voltage reading (1 point): ● 4.4 mV Table #1 – Measurements (6 points) : Trial # θ bench, initial direct compass reading (degrees) Distance from laser to mirror (cm) Distance from laser to optical bench (cm) θ mirror , direct compass or protractor reading (degrees) Flux/voltage recorded from photometer (mV) Flux minus background (mV) 1 50° 30 cm 19 cm 20° 115.5 mV 111.1 mV 2 60° 38 cm 27.5 cm 29° 214.6 mV 210.2 mV 3 70° 36.5 cm 30 cm 26° 146 mV 141.6 mV 4 80° 35 cm 30 cm 40° 168 mV 163.6 mV Sample calculation for flux – background (1 point) : ● Voltage Reading - Background Value =VR - BV 115.53 mV - 4.4 mV = 111.13 mV 2

Table #2 – Calculations (4 points): Trial # θ bench from distances/using trigonometry (degrees) θ mirror from distances/using trig; should = ½ * θ bench (degrees) θ mirror theoretical, from direct compass reading of θ bench (degrees) Discrepancy in θ mirror (% error) 1 39.3° 19.7° 25° 21.2% 2 46.4° 23.2° 30° 22.6% 3 55.3° 27.7° 35° 20.8% 4 58.9° 29.5° 40° 26.2% Which of the two methods for measuring θ mirror experimentally (from distances or from the compass/protractor) did you use when calculating the discrepancy? Why? (Your explanation should only be a sentence or two.) (1 point) ● The methods used for measuring θ mirror included the distances between the laser to optical and the laser to mirror. This method was used because it was determined that the values recorded by the distances could show a more accurate reference of the readings when compared to the protractor. Sample calculations for θ bench from distances, θ mirror from distances/using trig, θ mirror theoretical, and % error (2 points, 0.5 each): ● Arcsin (19 cm / 30 cm ) = 39.3° Is the discrepancy/% error of θ mirror comparable to the % error in your angular measurements, or is there an additional source of systematic error? (1 point) ● = 100 = 21.2% 𝐸𝑥?𝑒𝑟𝑖?𝑒?𝑡𝑎? − 𝑡ℎ𝑒?𝑟𝑒𝑡𝑖𝑐𝑎? 𝑇ℎ𝑒?𝑟𝑒𝑡𝑖𝑐𝑎? | 19.7−25 25 | × Is there an angle for which the reflected light is maximized? (1 point) ● No, there is also no direct correlation associated with the angle and the maximum mV that is reflected. There is also evidence of fluctuations that occur with the voltages due to light from the windows and many sources outside what was recorded. Using your answers to the previous two questions, can you conclude from your results whether the mirror is a perfect specular reflector? (1 point) 3

● Base d on discrepancy in θ mirror , the % error of our results (from 20%-26%) is greater than precision error (~10%), so I conclude that the mirror is not a perfect specular reﬂector. ● Theta mirror also does not perfectly represent ½ of the theta bench. 3.3.3 Diffuse Reflector (Total points: 15) Goal: Measure how the amount of light reflected by a diffuse reflector varies with the angle of reflection. *For this section, keep the laser fixed at a given θ bench and rotate the white card. It is much easier than trying to change the position of the laser. θ bench value, should be between 0 and 90 degrees for simplicity (1 point) : ● 40° What is the measured angle θ white card when the white card is perpendicular to the optical bench? (1 point) ● 0° The angle θ white card should be corrected to 0 degrees when the white card is perpendicular to the optical bench. What is the correction (in degrees) between your measured angle and 0 degrees? Show your calculation. (1 point) ● 360° - θ white card , direct compass = θ white card corrected value 360° - 350° = 10° Calculate the expected θ white card for the expected intensity maximum corresponding to specular reflection, based on your θ bench value and your correction from the previous part. This is t he angle at which you expect to see the maximum flux. (1 point) ● ½ q bench = ½ (40) = 20 degrees for maximum flux expectation. **For the table below, you may do more than 10 angles if you wish, but only 10 are required. You may also want to measure the background for each individual angle if you are in a lab station by a window/to make sure you have no V – bkg values; if you keep it the same or only measure it once, you can fill out the “background” column below with the same value all the way down. For the corrected angle, set it to zero degrees when the white card is perpendicular to the optical 4

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