HW2Problem_Set2_2023

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Feb 20, 2024

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Audrey Gabbard BME 6931 Problem Set 2 – Due Friday September 15, 2023 at 5:00 PM EST Total 150 points 1. (50 points) – Set up a Michelson interferometer to measure the wavelength of a light beam, and also to measure the index of refraction (n) of a substance. Refer to the accompanying diagram. The light source (a tunable laser) at left shines light onto a beam splitter. The split beams each hit a mirror (M1, M2), one of which is movable (M2), then recombine at the beam splitter and continue to a detector for light intensity. You will write Matlab code to detect the intensity of the recombined beam as a function of the position of M2. A. Assume that both M1 and M2 are initially set to be 10 cm from the beam splitter. Move M2 away from the beam splitter in 0.025 µm increments over a distance of 2µm. At each position of M2 (including the 10cm initial position), compute the resultant intensity of light at the detecto r. Repeat the calculation for wavelengths of light between 350 and 800 nm, in 50 nm increments. a. Plot your intensity data for each wavelength separately, in a 5 row X 2 column array (10 different wavelengths). Keep the scales for the abscissa and ordinate identical across plots. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 350nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 400nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 450nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 500nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 550nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 600nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 650nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 700nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 750nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 800nm Intensity Plots at each Wavelength on M2"s distance from beam splitter
b. For each wavelength, indicate the distance that the mirror was moved between two maxima in your plots. Then use that value to calculate the wavelength of the light , which should match the wavelength that you introduced into the interferometer and quantified by moving M2. c. In words, indicate what measurement is most fundamental for your calculations, and which also determines the accuracy of the interferometer. The most important measurement for the calculations is …………………………………….. Something with the lens????? 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 350nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 400nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 450nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 500nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 550nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 600nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 650nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 700nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 750nm 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Distance (um) 0 0.5 1 Intensity (W/m 2 ) Intensity at 800nm Intensity Plots at each Wavelength on M2"s distance from beam splitter X 0.7 Y 1 X 1.4 Y 1 X 0.7 Y 1 X 0.35 Y 1 X 0.9 Y 1 X 0.45 Y 1 X 0.8 Y 1 X 0.4 Y 1 X 1 Y 1 X 0.5 Y 1 X 1.1 Y 1 X 0.55 Y 1 X 1.3 Y 1 X 0.65 Y 1 X 1.5 Y 1 X 0.75 Y 1 X 1.2 Y 1 X 0.6 Y 1 X 1.6 Y 1 X 0.8 Y 1
B. Some guidance for computing intensity: a) You’ll need to calculate the phase shift between the light paths that was introduced by moving M2. b) Next, calculate the sum of two sine waves with that phase shift. a. Sample the sine waves at 0.1*π increments through one complete cycle (2π) and add the values at each sample point. c) To compute intensity, square each value of the summed sine wave (recall Intensity is proportional to Amplitude 2 ). d) Sum the 21 values and divide by 21 to achieve the average intensity. 2. (30 points) Using the interferometer from problem 1, we will measure the index of refraction (n) of a thin piece of glass. A. Introduce into the middle of the light path from the beam splitter to M1 (at the 5 cm location) a piece of glass 1mm thick. For the purpose of this problem, assume that the glass has index of refraction n = 1.4. a. For lambda = 500 nm, plot the intensity profile while moving M2 as in problem 1 without and with the piece of glass introduced into the light path. Plot both profiles on the same graph. M1 is 5cm from beam splitter Thickness of glass, h = 1mm Index of refraction of glass, n = 1.4 Lambda = 500nm Plot intensity vs distance twice without glass and then with glass in light path on same graph
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Huygen’s interpretation of light refraction. Draw your own diagram, with equally space radiating centers at the surface of the glass, to explain the angle of refraction. b. If you received the data that you plotted, knowing only the thickness of the piece of glass, how would you use the information to calculate n? Write Matlab code to generate your plots and comment on your thought process for each step. Imagine not knowing n (index of refraction), inference from the two plots with and without the glass, then go backwards to prove the calculation of n 3. (20 points) Using the wavelet approach of Huygens, and the attached diagram, describe how the plane wave incident in air at 60° from vertical to a flat piece of glass is refracted in its direction through the glass. The diagram is from lecture, and the incident plane wave in the diagram is not 60° to the surface of the glass, so you’ll need to draw your own diagram, based on the diagram pictured here. Draw on paper the excitation of each atomic center at each step of time as a radiating circle, with the circle diameters in the glass as 2/3 the diameter of the circles outside of the glass. Draw a straight line across the fronts of each set of wavelets at each point in time Measure the refraction angle on your drawing with a compass and report the actual value. Does your measured angle and refractive index values approximately follow Snell’s Law? Show your work.
4. (5 points) From the ppt of Week 3, Lecture 2, slide 8, perform the last algebraic steps [Substitute (13) into (10)…] and arrive at equation 14. Show clearly each step of your work. INSERT PICTURE OF WORK DONE ON PAPER Is equation 14 correct? o Yes! One important check in a physics problem is to determine if the units cancel and are correct. Equation 14 should have the units of coulomb (C) for charge (Q). Show clearly each step of your work. Q = 18 π d g V η 3 v f 3 2 ρg ∗( 1 + v r v f ) Q is charge o Units: Coulomb or FIND CONVERSION …………………………………… d is distance o Units: meters g is gravity, 9.81m/s^2 o Units: m/s^2 V is voltage o Units: Volts η is viscosity (of air) o Units: Pa*s or kg/(m*s) ρ is rho (of oil) o Units: kg/m^3 v f is falling velocity o Units: m/s v r is rising velocity o Units: m/s 5. (20 points) Calculate the velocity of electrons moving through the column of an electron microscope . a. From the example equation in the lecture relating 100,000 eV of kinetic energy to particle velocity (100 keV = (1/2)mv 2 , and the deBroglie relation l = h/mv, generate an expression relating v to l. Symbols are: e = electron charge, m = electron mass, c = speed of light, h = Planck’s constant. Show your work. Momentum p = mv (I think)
Lambda = h/mv = h/p b. Write a Matlab script, to calculate velocities and wavelengths when electrons are accelerated by the high voltage transmission electron microscope (TEM) (1MeV), intermediate voltage TEMs (400keV, 200keV), standard voltage TEM (100keV), 30keV typical of an SEM, an SEM adjusted for a landing voltage of 2.5keV and 1keV, and 200V more typical of a cathode ray tube. c. Plot wavelength(lambda) and velocity vs these electron energies, using the left y- axis for wavelength and a second y-axis plotted at the right side of the graph for velocity. d. Comment on the values you plotted, and indicate if you think there are problems with any of the values. e. Research the fastest serve recorded in men’s tennis. World’s Fastest Men’s & Women’s Tennis Serves Ever Recorded (tenniscompanion.org) a. Using typical metrics for a tennis ball, calculate the associated wavelength of the tennis ball during the serve. Wavelength,l ambda during serve = ¿ b. Calculate the wavelength for a baseball traveling at the same speed. Wavelength,lambdabaseball = ¿ c. Comment on the different values. i. The difference in the tennis ball and baseball involve 6. (10 points) Compare a TEM to a SEM. a. Draw the elements of the electron optical train for transmission (TEM) and scanning (SEM) electron microscopes. b. List the elements of the TEM that could be used in construction of a SEM without modification. c. List and indicate the functions of the elements that are found only in the SEM.
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d. For these SEM elements, indicate why they are placed where they are placed. e. What electron detector types are used in SEM? Research and report on the energy range of electrons captured using each detector. 7. (20 points) Re-visit the layer 2 pyramidal cell Narration, and inspect carefully the spines on the dendrites. If you were permitted to generate up to 6 classes of spines from qualitative expression, what would they be? Feel free to choose fewer than 6 categories. Draw your examples, and in no more than a few bullet points, define their features. Draw examples of spines that are most difficult to categorize. Trace along the main apical dendrite (straightest route to the brain surface). Approximately divide the length into 4 equal segments. Record the number of each of your types of spines in each of the 4 segments. Send your spreadsheet of values. Comment on any observations or conclusions you draw from your data.