By: Adriana Alvarez, Grace Libby, and Saleena Son

For our group project, we focused on planetary albedo and the reflectivity of our Earth. In order to do this we used a small solar cell connected to a multimeter, a laser pointer, and objects to symbolize different parts of our planet like a brown bag for soil, a mirror, spinach for vegetation, ice, and aluminum foil.

In order to conduct our experiment, one would first have to gather the “initial” light of the laser pointer by shining it directly on the solar cell and recording it. Next, they would choose an object to gather reflectivity like the paper bag, for example. This person would then hold the laser pointer at a 90* angle shining on to the bag and then move the solar cell to catch the reflection. They would then record the number that showed up on the multimeter. To record the reflectivity, the person conducting the experiment would then divide the reflected light by the incident light. From there they would go on to calculate the percent error. To do that, the would subtract the theoretical amount of reflectivity of the object (which was listed on the lab handout) from the recorded reflectivity and divide that answer by the theoretical reflectivity. Once they got that answer, they would multiply it by 100 to get the percent error.

The process of narrowing down our project took some trial and error. We initially thought we wanted to focus on albedo of different sized and colored blocks of ice. We quickly learned that ice would not only be able to maintain frozen, but it also would be hard to measure reflectivity. We also originally were going to be measuring both absorption and reflectivity which proved to be too much for the project. With a little guidance form the professor we decided to focus on reflectivity on objects that could represent different parts of earth (grassland, ocean, snow, ect.). Next we started testing out materials and through more tests we decided to use spinach, ice, a mirror, a brown bag, and aluminum foil. They showed a good range of the albedo effect and had promising results. Then we started creating our equations and analysis that was to be used by the people doing the experiments. This includes Incident/Reflected=reflectivity and the equation for percent error. We go together to run the experiment to make sure it worked and was ready for the big experiment.

 

RESULTS:

Table 2. Reflectivity of everyday items

Treatment:	Incident:	Reflected:	Reflectivity:	% Error:
Mirror:	0.36	0.32	0.88	3.8%
Ice:	0.36	0.33	0.92	1,940%
Spinach (Grass):	0.36	0.21	0.59	136%
Aluminum:	0.36	0.22	0.61	166%
Brown Bag (Soil):	0.35	0.19	0.54	170%

 

Reflectivity=ReflectedIncident

% Error = # Experimental-#Theoretical#Theoretical100

 

Analysis Questions:

1. Does the measured amount of reflectivity values compare to the widely accepted  reflectivity values in Table 1? Which item has the greatest percent error? The least?

 

The results obtained in this lab represent that the experimental values calculated are not comparable to the theoretical values that were gathered from data provided by the professor as well as various other sources. However, the most comparable values were that of the matte aluminum and the least comparable was the ice.

 

1. How does the reflection of more matte materials differ from more reflective materials?

The mirror and the ice represent more reflective materials and both had better reflectivity values. During experimental design, we knew that the mirror would act as a “control” in this experiment because it is widely known to have high reflectivity. However, items such as the spinach and the brown bag has significantly less reflectivity because both do not have the physical appearance of reflectance, nor do they have a high measured reflectance.

 

1. Based off of this experiment, what do you believe would be the reflectivity of substances like sand, soil, or ocean water?

Since it was found that ice was the only item that is naturally occuring and had the highest reflectance, it follows that the ice caps on earth also have high albedo. If we think more about the effects of global warming and having our earth lose the ability to reflect UV rays if it was covered in dark colored land or grass, this demonstrates the urgency at which we should be addressing this environmental issue.

 

Other Recommendations

There were several issues with the data presented in this lab. Although the content of this experiment strives to accurately represent the albedo effect, it must be explained that when the affect is measured on such a small scale it can drastically skew the results. Further exploration into the theoretical values shown in the lab are necessary, not only to obtain more generalizable results about reflectance but to create a better understanding about the albedo effect overall. As shown here, the high percentage errors represent possible errors either in the way participants conducted the lab or most likely issues with the values used in calculation, with the exception of the “control” which was the mirror. For future research and experiments, this data serves as a area of exploration and critical thinking that is one main objective of designing this lab.