Mohamed Abdi
Group: Abukar, Ellias, Gemetrum
05/02/18
Phys 2710-01
Lab 12 – Distance and Polarity of Light
Purpose:
Polarization is a property exhibited by the electromagnetic wave that helps us to understand the orientation in their field oscillations. We are determined to establish the mathematical relationship or equation between the distance from the source and the intensity. In this experiment, we recorded information on three variables that are the angle between the polarizers in degrees, the intensity of light in luxs and the distance in centimeters (cm). According to the experiments, the three variables are related. The relationship between light intensity and illumination is that increase in the distance from the source leads to a decrease in the amount of light intensity. The graph gives us the equation illum=mD+b.
The main aim of carrying out the second experiment was to investigate the polarity of light and was carried out by using polarizers and rotating them to make sure that the light seen by our eyes is lined up in a single direction and the second polarizer helps us to note that light can pass through according to the polarizers orientation. The results give us curves that at different angles the amount of illumination varies. This mainly depends on the position of the two polarizers.
Procedure:
Part 1
We all know that the amount of light that strikes the destination decreases with increase in the distance between the source and the destination. In this experiment, when recording the intensity of light in various places, we normally unite the light sensor to channel one of the interfaces and switch it to 600 lux range then put the light sensor in its holder then have it at one end of the track. The light source should be placed at the opposite end of the track, and the openings should be rotated to ensure that the largest circular opening is obtained. To ensure that the meter window displays light intensity, open the “32 light brightness dist in the physics using a vernier folder. Ensure also that lights in the room are turned off because this helps in darkening the room because having a room that is dark increases the chances of obtaining better results. Reflective surfaces should be kept away from the bulb.
Shift the light sensor until it is closer to the source at a reading of 550lux. You can make adjustments to achieve an even distance recorded in centimeters in a case where the sensor is 600 lux, and it would be better if it is moved away. Collection of data begins when the collect button is clicked, and the keep button helps in continuing to collect the data until the end. When the value of the light intensity on the screen stops changing, keep button and then typing the distance between the light source and the light sensor should lead you to the ok button that records the value of intensity, and a graph is plotted. The sensor can now be adjusted in increments of 1cm away from the light source as you take points along the way until there is a set of 15 points of the data.
Part II. Get two polarizers that rotate from their kit and place them in between the light sensor and the source of light while ensuring that the numbers on the polarizers can be seen at least one of them can be seen. The two polarizers should be in the same position and that the little white lines point at the same angle that is zero. After this, it will be good ensuring that the light sensor should not go beyond 550 lux and adjust it to have it closer if the reading is too low. It is good to note that even when the polarizers are aligned, the polarizers also cut down on some of the intensity. Thus, when the polarizers are arranged at an angle of 0 and the sensor on the 600 lux setting if it is possible, open the file "28 polarization of light in the folder that has physics with the vernier. To start collecting data, click the collect button and also ensure that the reading on the light sensor is less than 600 lux. When the value off the intensity that is displayed on the screen does not move in any direction using the button keep and then measure and key in the angle between the two marks and record the points by clicking ok. On the graph, the first point will be plotted. To continue with the process, turn one of the polarizer 20 degrees and repeat the step to record the next point. This process should continue until it reaches 360 degrees.
Analysis
Part I
Distance (cm) Intensity (lux)
23.4 550
24.6 508
25.6 471
26.6 439
27.6 408
28.6 381
29.6 358
30.6 335
31.6 298
32.6 297
33.6 280
34.6 265
35.6 252
36.6 238
37.6 226
From the data collected, a graph of illumination in lux against the light intensity portrays an inverse proportionality in that increase in the distance between the source and destination leads to a decrease in the intensity of light falling on the object. The gradient of the graph is -24.48 lux/cm while his y intercept b is 1097lux the highest light intensity that would be achieved (produced at the source)
Part II
The angle between polarizers(degrees) Intensity (lux)
0 499.3
20 471.8
40 335.2
60 167.7
80 30.9
100 5.1
120 90.9
140 223.7
160 369.5
180 497.4
200 402.9
220 289.7
240 177.5
260 49.8
280 3.5
300 79.6
320 281.7
340 398.1
360 501.7
According to the data collected that led to the plotting of the graph, the relationship between the illumination and the angle gives a wave and can be understood using the equation illum=A*cos(Bx+C)2+D the equation is a curve fit that helps analyze the relationship in the data. The set of data collected was compared using (cos2ɵ), and the data shows that it obeys Maul’s law pattern.
Overall Analysis
The experimental data collected is an indication that Malu’s law pattern is obeyed and though there are slight discrepancies that exist between the calculated data and the experimental data the reasons are mainly due to slight imperfections that exist in the polarizers, and we can also assume that the change in the LDR resistance portrays a linearity in proportion with the intensity of light. The polarizers used helped us deduce that light intensity from a polarized source of light has the tendency of decreasing and increasing continuously. Depending on the angle, lenses of the polarizer let fewer amounts of light directions to pass through and also allows larger light direction to move through in different angles. Thus the polarizer rotation produces increasing intensity as well as diminishing intensity depending on the angle.
Error Analysis
In the error analysis we are going to concentrate on the qualitative errors and their causes because we have not dealt with calculations involving the coefficients and relationship between variables in an equation. During the preparation of the experiment two, the probable error that could have occurred was caused by the differences between the actual data and calculated data which is mainly caused by polarizer faults. Having little information regarding the light sensors and the polarizers is another probable cause of errors and could not give us a 100% correct figure as it should. There are errors that are associated with raw data collection including the angle and the distance these are mainly due to the rounding off of the figures collected and will later have an impact on the final results as well.
Conclusion
In the laboratory, the experiment we measured the intensity of light at different distances and found out that increase in distance leads to a reduction in the light intensity illuminated. This can be explained by the reason that light molecules the photons spread in all directions and that some are lost before heading to the destination. In the realization of the polarity of light, we are able to understand that this property allows us to form a dark image. From work above, when we qualitatively analyze the information concerning polarization, we are able to understand what it entails. The quantitative analysis of this law helps us understand the theoretical concept, and that is the Malu's law. The further the distance the lesser the light illuminated to the destination and vice versa. The error levels are very low, and that makes us believe that the relationship we have shown about the two items matches.
In the second experiment, we have been able to demonstrate the relationships between light intensity and the angle of the polarizers which has shown a continuous decrease and increase depending on the angle rotation of the polarizer. According to the analysis and explanation given above, the relationship matched Malu's law of polarization, and this creates confidence in us bearing in mind that that we had very low levels of errors. The experiment helped us understand more deeply the light intensity and angle rotation. The role of this is that it gave us a better understanding of the activities that take place in our daily lives concerning the electronics and electricity in the experiment.