To study Brownian motion, Bob, a student at the University of Ottawa, used his camera to capture the positions (i.e. displacements) of 50 microscopic dust particles floating on the surface of the water of his aquarium. By setting his camera to record 10 frames per second and noting down each particle's 2D displacement for each recorded frame, he managed to obtain the following mean-displacement vs time graph: Mean-square disp. (cm²) 1600 1400 1200 1000 800 600 400 200 0 0 20 40 60 80 Time (s) 100 120 140 a. Use the above mean-displacement graph to roughly approximate the diffusion coefficient D of the dust particles with units of µm² /s. b. From the diffusion coefficient estimate in a), calculate the root mean- square displacement expected between each consecutive frame? c. Are the diffusion coefficient D and mean-square displacement calculated reasonable for a microscopic particle, or did Bob make a mistake in his calculations?

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To study Brownian motion, Bob, a student at the University of Ottawa, used his
camera to capture the positions (i.e. displacements) of 50 microscopic dust
particles floating on the surface of the water of his aquarium. By setting his
camera to record 10 frames per second and noting down each particle's 2D
displacement for each recorded frame, he managed to obtain the following
mean-displacement vs time graph:
1600
1400
1200
2 1000
V
800
600
400
200
20
40
60
80
100
120
140
Time (s)
a. Use the above mean-displacement graph to roughly approximate the
diffusion coefficient D of the dust particles with units of um? /s.
b. From the diffusion coefficient estimate in a), calculate the root mean-
square displacement expected between each consecutive frame?
c. Are the diffusion coefficient D and mean-square displacement calculated
reasonable for a microscopic particle, or did Bob make a mistake in his
calculations?
Mean-square disp. <r?> (cm²)
Transcribed Image Text:To study Brownian motion, Bob, a student at the University of Ottawa, used his camera to capture the positions (i.e. displacements) of 50 microscopic dust particles floating on the surface of the water of his aquarium. By setting his camera to record 10 frames per second and noting down each particle's 2D displacement for each recorded frame, he managed to obtain the following mean-displacement vs time graph: 1600 1400 1200 2 1000 V 800 600 400 200 20 40 60 80 100 120 140 Time (s) a. Use the above mean-displacement graph to roughly approximate the diffusion coefficient D of the dust particles with units of um? /s. b. From the diffusion coefficient estimate in a), calculate the root mean- square displacement expected between each consecutive frame? c. Are the diffusion coefficient D and mean-square displacement calculated reasonable for a microscopic particle, or did Bob make a mistake in his calculations? Mean-square disp. <r?> (cm²)
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