Henry M. Gunn High School
Optical Rotation: Final Attempt
What is the purpose of conducting this experiment a second time? We want to optimize our results by identifying the problems with the last experimental design and optimize it to achieve more accurate results.
We conduct the experiment a second time so we can isolate more variables and achieve more accurate results. Many of the problems we encountered in the first trial could have been solved through automation, so that’s what we did in the second experiment. We decided to automate the second polarizer's rotation with a servo to limit human error. To make the experiment more cost-effective, we significantly lowered the costs for the experimental set-up as well.
Laser & Polarization
5V 650nm Laser Diode x 1: $6.50
Mount for Laser x 1: $0.10
MTO-laser Metal Aperture and Support Component x 1: $17.79
Transistor x 1: $0.50
BOWER Digital Linear Polarizer x 2: $7.99
58mm to 55mm Step-Down Ring Adapter x 2: $3.99
55mm to 58mm Step-Up Ring Adapter x 1: $3.99
Laser Cut Plastic Gear x 1: $0.50
Mount for Polarization x 2: $0.15
- Light Dependent Resister
HobbyKing HK15328A Digital Servo x 1: $21.32
Pin to DC Power Adapter x 1: $0.95
DC to 12V Outlet Adapter x 1: $6.99
Laser Cut Plastic Gear (Replica) x 1: $0.50
Light Dependent Resistor (LDR) Equipment
LDR x 1: $1.99
Analog to Digital Converter x 1: $8.99
Mount for LDR x 1: $0.15
Raspberry Pi x 1: $34.98
USB Wall Adapter x 1: $3.39
USB Male-to-Male Cord x 1: $5.00
Wireless Internet Connection x 1: $0.00
Digital Ocean (DO) Server x 1: $10.00
10 mm glass Cuvette x 1: $14.99
20 mm glass Cuvette x 1: $21.99
- External Set-up
27" x 12" Wooden Base x 2: $1.75
Breadboard x 1: $5.69
Male-To-Male Pins (total price) x 12: $2.33
Female-To-Female Pins (total price) x 2: $2.33
Male-To-Female Pins (total price) x 2: $2.33
1" Bolt x 1: $0.18
2" Bolt x 1: $0.32
1/4" Nut x 1: $0.07
2" Wood Screw x 2: $0.44
0.5" Wood Screw x 1: $0.05
5/8" Wood Screw x 4: $0.17
0.25" Machine Screw x 4: $0.05
Protocol and Procedures:
- Prepare experimental set-up according to Diagram A such that all mounts, laser, LDR, servo and polarizers and secured in their corresponding positions.
- Prepare experimental set-up according to Diagram A such that all mounts, laser, LDR,
servo and polarizers and secured in their corresponding positions.
- Connect LDR/Servo to corresponding power and information pins on Arduino
- Load Project Querb System Code into Arduino
- Power on laser
- Turn off lights in dark room
- Calibrate servo to “zero” position at the blanked control
- Prepare cuvettes with glucose sugar solution by rinsing both the 10mm and 20mm cuvettes with distilled water and pouring sugar solution to top of both cuvettes. Cap both cuvettes.
- Insert both cuvettes along the laser line on top of the cuvette mount and run servo program on Arduino (found in QUERB-system.py file)
- Collect data printed from the serial monitor
Improvements from the Last Experiment Made:
After attempting to conduct this experiment in the classroom, we have made significant
improvements to our set-up in order to obtain more accurate results in accordance with an
accepted specific rotation value.
How we obtained an accepted value through ORD
Dark Room Laboratory
One of the problems we have identified which potentially affects the accuracy of our results is the noise caused by light in the surrounding environment. Background light, including sunlight and room lights, greatly affects the photodiode readout and its relative accuracy. By changing our experiment location from a sunny classroom to the photo classroom’s darkroom, we are able to limit ambient light pollution and ensure our photoresistor measurement is accurate. We also made sure to remove all bright electronics and use flashless-photography near the sensor to further ensure accuracy.
Secure Mounting and Polarizer Mounting Methodology
We laser-cut mounts for each of the polarizers. The mount design is a rectangle with a spherical hole at the height we wanted the polarizer to be at (3.5”). After testing the setup, we made a final model by layering laser-cut wood. We glued the mounts on to the board where the appropriate plots were located. Our base is constructed with two 27” x 12” plywood boards which are screwed together using four ⅝” wood screws to provide “top” (of 0.25” depth) and “bottom” (of 0.75” depth) parts of the base. Within the top base only, we cut small plots into which the mounts are inserted. This allows for any needed modifications/exchanges of mounting while also supply stable support for each mount. Two 0.25” by 3.5” plots are cut from the top base 7.5” and 18” in from the leftmost side of the base to host the polarizer mounts. Both polarizer mounts are made of 5.5” tall plywood boards in which a 1.5” diameter aperture is drilled in each. The center of these apertures are 3.5” above the surface of the top base and centered laterally (1.75” in from either side of the board). A 55mm to 58mm step-up ring adapter is epoxyed in this same way to polarizer mount #2. Polarizer #2 can then be screwed onto its mount. To allow rotation of Polarizer #2, we screw a 58mm to 55mm step-down ring adapter to the open side of the polarizer and glue a 58mm diameter, 56 teeth, plastic gear to the adapter. Implementing this additional ring adapter ensures that no glue remaining on the back of the gear will block the manufactured rotation mechanism in the polarizer.
Automation of Experimental Components: Limiting Human Error
In the optimized experiment, we made use of a Sparkfun Arduino board to control a servo that rotated the second polarizer. The photoresistor was also hooked into the board, which allowed us to record light levels during the experiment. Using this electronic control and measurement system greatly increased the experiment’s precision and allowed us to complete a much larger volume of trials in a shorter amount of time. A simple program on the board allowed us to easily modify the number of trials, photoresistor resolution, and servo speed to however the experiment saw fit.
Use Distilled Water
In the solutions, we used distilled water instead of regular tap water. If regular tap water were to be used for the experiments, ions and other particles present in the water could potentially affect the polarization. Regular tap water contains natural minerals or other potentially chiral substances that could affect the resulting linear polarization rotation from our sugar solution. Conversely, using distilled water utilizes the process of distillation, resulting in a reduction of potential error in the final readings.