Investigating optical properties of Jelly.

To form the Jelly, a sachet of ready-to-make strawberry Jelly was used and all instructions on the packet were followed to obtain a well-made Jelly. An electronic water bath was used to keep the jellies at different temperatures. As the Jelly is heated, the water in it would expand and thus, it was hypothesized that higher the temperature, lower would be the optical density of the Jelly and hence, smaller the angle of refraction and the refractive index.

VARIABLES:

Independent Variable:

Dependent Variable:

Controlled Variables:

APPARATUS AND CHEMICALS:

PROCEDURE:

1. Excess of the same kind of Jelly was prepared by following the manufacturer’s instruction at the back of the packaging.
2. The white paper board was laid out flat on the work table and the low walled rectangular bowl was placed on top of it.
3. Using a pencil and a ruler, the low walled rectangular bowl was traced out on the white paper board.
4. With a pencil, ruler and the protractor, an incident ray was drawn on one side of the traced rectangle.
5. One the incident ray, three
6. Using a sharp brimmed rectangular bowl, a cuboid of Jelly was cut out and placed on the low walled rectangular bowl.
7. The piece of Jelly was completely wrapped with one layer of LDPE cling wrap and any air pockets in it were released to ensure a tight wrap.
8. The thermometer was inserted into the top right corner of the Jelly.
9. The entire setup of Jelly in the low walled rectangular bowl was cooled to 10oC in the electronic water bath and the temperature was maintained until it was to be used again in step 12.
10. Using a pencil, ruler and the protractor, an incident ray of light at 45o was drawn entering the rectangle on the white paper board.
11. On the incident ray, three tack board pins were stuck so that they were all collinear.
12. The Jelly was placed on the white paper board inside the rectangle drawn in step 3.
13. From the opposite side of the Jelly, the three pins were viewed in a way that they all seemed to be collinear.
14. Making sure no parallax error was caused, the fourth pin was put down on the opposite side of the Jelly making sure that it too lined up perfectly with the three pins on the other side. The same was repeated with the fifth and the sixth pin.
15. The Jelly was removed and using a pencil and a ruler, a straight line was drawn through the three locations at which the fourth, fifth and the sixth pin were planted.
16. Procedure 13 and 14 was repeated four more times to obtain five sets of readings.
17. The entire procedure was repeated for all other temperatures: 20oC, 30oC, 40oC and 50oC.

Safety Precautions:

1. Ensure a safe distance from the electronic water bath and use gloves while handling the hot water tray.
2. Ensure the necessary dimensions of the low-walled rectangular bowl and the sharp brimmed rectangular bowl are the same.
3. Ensure pins are not too thick and they are not bent.
4. While tracing the path of the pins, adjust height of viewing to ensure no parallax errors. Preferably, close one eye to isolate unnecessary lights.
5. Ensure thickness of cling film is negligible as it can have its own refractive properties.
6. Ensure straight lines for the rays and make sure the normal line drawn are parallel to the other.
7. Make sure that pins are appropriately spaced apart so that a more accurate determination of angle is allowed.  

Labelled Diagrams:

Figure 1: Setting up Jelly onto high-walled rectangular bowl.

Figure 2: The different parameters of the experiment.

RAW DATA COLLECTION: (Sample)

RAW DATA PROCESSING: (Sample)

The values for temperature can be plotted against Refractive index (n); refractive index on the y-axis and temperature of the Jelly on the x-axis.