Keith Chan
Physics Mini Investigation
1. Seeing Sound
In order to be able to observe sound wave signals, we spoke in front of the microphone which was connected to the computer and uses a program to plot the amplitude of the sound wave against time. Since human voice varies from words to words (even with when singing a constant tone) and can hardly produce a steady tone (i.e. same waveform). The graph is reproduced using a spreadsheet program as follows (since the screenshot function was not working on the computer):
Sound Censor against Time
from 0 to 1000ms
0.2 0.2 0.1
Sound Censor / V
0.1 0.0 0.000 -0.1 -0.1 -0.2 -0.2 -0.3 -0.3
Uncertainties is too small to be shown
100.000 200.000 300.000 400.000 500.000 600.000 700.000 800.000 900.000 1000.000
Time / ms
Sound Censor against Time
from 500 to 650ms
0.2 0.2 0.1
Sound Censor / V
0.1 0.0 500.000 -0.1 -0.1 -0.2 -0.2 -0.3 -0.3
Uncertainties is too small to be shown
520.000
540.000
560.000
580.000
600.000
620.000
640.000
Time / ms
As we zoom into the time period 500 to 650 ms, Maria was trying to produce a stable tone (e.g. ah-h-h-h). Though it sounds the same to human, it looks similar but when closely examine, they have a varying amplitude as well as waveform owing to the
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variation in vibration of our vocal cords.
2. Fan Speed
We are supposed to calculate the speed of the fan by adjusting the flash rate of the strobe. The rotational speed of the fan can be estimated by following this logic: 1. The flash rate of the strobe equals to the rotational frequency of the fan 2. However, since it is possible that the rotational frequency of the fan is higher than the strobe, it is best to adjust the flash rate of the strobe using top-down method (i.e. starting from the highest frequency and record the frequency when the fan appears to be stationary) 3. Then, divide the flash rate by the number of blades on the fan since the same blade has to complete one revolution. 4. The rotational speed is the frequency. Since we do not have adequate time, we have taken two readings only: Voltage / V Current / mA Power / W 2.0 1.5 200 200 0.4 0.3 Flash Rate / flash min-1 Rotational Speed / Hz 3307 2169 1102 723
3. Inverse square law for light
1 x2
0 0.000025 0.0001 0.000225 0.0004
Light Intensity / Lux 3.98 2.49 2.12 1.91 1.75 0 0.005 0.01 0.015 0.02
Distance x / m
Light Intensity against Distance
4.5 4.0 y = 0.8555x-0.0965 R2 = 0.9896
Light Intensity / Lux
3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0.000 0.000
0.000
0.000
0.000
0.000
0.000
0.000
2 0.000
0.000
uncertainties is too small to be shown
Distance / m
Keith Chan
We then repeated the experiment but using a mounted light which produces mainly ultraviolet light. The measuring unit is Wm-2. The follows are the data:
Light Intensity / Wm-2 38 11 6 4 3 2 2 1 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035
Distance x / m 0 0.000025 0.0001 0.000225 0.0004 0.000625 0.0009 0.001225
1 x2
Light Intensity against Distance
60.0 50.0 y = 0.3147x-0.2773 R2 = 0.8662
Light Intensity / Wm^-2
40.0 30.0 20.0 10.0 0.0 0.000
0.000
0.000
0.001
0.001
0.001
0.001
0.001
uncertainties is too small to be shown
Distance / m
From the graph, we could see that the light intensity shows a inverse relationship with the distance from the light source (x) yet the value is no so close to
1 . x2
4. Comparison of Cooling Curve
In this experiment, we are trying to observe the effect of forced convective cooling with the use of data logger. We will plot the a graph of temperature against time for the two samples (one that cools in normal condition while the other is forced cooled by a electric fan). We took a screenshot of the plotted graph in the data logging program and is as follows:
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Keith Chan
Green line – Forced Convective Cooling
Red line – Normal Condition Cooling
In the graph, the green line shows data of sample which is cooled by forced convection while the red line shows the one which is cooled under normal condition.
Temperature against Time
45.0 40.0 35.0
Temperature / oC
30.0 25.0 20.0 15.0 10.0 5.0 0.0 0.000 y = -0.0146x + 29.502 2 R = 0.0482
20.000
40.000
60.000 Time / s
80.000
100.000
120.000
Uncertainties is too small to be shown
↑Best fit line for red line.
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Keith Chan
Temperature against Time
50.0
Temrperature / oC
40.0 30.0 20.0 10.0 0.0 0.000 20.000 40.000 60.000 Time / s
↑Best fit line for green line.
y = -0.0228x + 41.115 R2 = 0.4057
80.000
100.000
120.000
Uncertainties is too small to be shown
If we find the best fit line for both lines, we could see that the slope of the green line is steeper than the red line which complies with the hypothesis that with forced convective cooling, the rate of cooling will be greater than cooling under normal condition.
5. Study of damped harmonic motion
In this experiment, we are investigating a damped harmonic motion due to the small inertia and the significant air resistance. We have collected the distance between the ball and the distance sensor using a data logging program and have plotter a graph as follows:
As you can from the graph, the amplitude of the distance between the ball and the sensor decrease over time which shows a damped harmonic motion. Note: The sudden rise in amplitude is because we have added more force to the ball by pulling it further back from its original position. The period will remain constant throughout the experiment because the ball slows down as the harmonic motion damps. Thus, the time taken for the ball to travel back and forth remains unchanged.
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