Everything about Geometric Optics

The most fun experiment ever!

We had our ray box experiment, but what is a ray box first? It is a box (obviously) that has a light source inside it (with what we were using, it was an incandescent light bulb) and slits that when adjusted, produces little light rays. When turned over, it has another slits but with colors (specifically red, green and blue respectively). With this amazing (yes, I'm too amazed) device, we observed and studied lenses and mirrors and their properties.

We started out with adding the primary colors and observing the secondary colors they produce. With this experiment, we were able to explain the nature of colors to produce white light (RGB) and the color produced when red, green, and blue paints are mixed (black)

I'm not sure if these rays can produce white light if reflected into a focus... hmmm....

Second, we created rainbows using the acrylic rhombus prism by placing it correctly in line with a ray of light from the raybox. It was observed that the rays of visible light seen follows Snell's Law by computing it with the given information on red light and violet light. Violet light was the most refracted whereas the red light was the least refracted, which can be seen on the picture below:

Primary Rainbow on the left, and secondary rainbow on the left

The secondary rainbow was produced because of the two paths taken by the light. I forgot the exact value but I think the primary one is 42 degrees and the secondary is 57 degrees refracted from the normal. However, when the primary colors are shone into the prism, it produces parallel rays.

Notice that the secondary "rainbow" is a mirror image of the ray passed through it.

We deduced that the rays passes through the same path taken by the white light, but the primary colors cannot disperse because the are already monochromatic. 

The nature of spherical mirrors were also observed by shining five light rays into the mirrors and sketching/tracing them on the paper and measuring the focus to see if it follows the relationship between focus and radius of curvature for mirrors.

There were two more "mini-experiments": These were the the Total Internal Reflection and the Apparent Depth Method.

Total Internal Reflection is observed when no transmittance of light exists. This happens when the light passes through the prism or object with the critical angle. We drew the path of light and noticed that the critical is half the angle b/w incident and reflected rays.

With the Apparent Depth Method, we had to find the index of refraction n of the material (acrylic) but putting a biconcave lens in front of two light rays which are a bit far away and focused by the lens. When the Rhombus is placed on top of the part of the paper where the focus is, the focus shifts. We measured the difference of these foci and the thickness of the rhombus, leading us to the index of refraction of the object.

This experiment was really, really fun, but took quite a long time. It was relatively easy to do and understand, but the length of work and paper and analyzing and drawings makes it hard to do, and to finish :)) But the best thing is, we enjoyed doing it and it was my favorite so far.

How Intense is Light?

Not exactly how it looks like, but this shows how the experiment was done.

So here's the very first experiment my groupmates and I did for the year 2012! :)

It was very simple. We connected a light sensor to LabQuest and then measured the light intensity in lux of the  light from a source with respect to the sensor's distance from it. At first the readings were the same (~1cm to 14cm) until at 15cm, the light intensity reading dropped, and so on until it became constant. This constant reading is said to come from the environment and must have been set to zero.

We had many questions for this experiment: Why did the light intensity became constant? Was the light sensor's minimum reading supposed to be not zero? Did we note a wrong set of data?

Somehow, these questions made sense as we discussed how to write this paper. For the previous technical reports we did, we always cut the parts of the report to each member and then compile them on the end of Sunday. This lead to my incomprehension of the previous experiment we did (the one with PV diagrams). It was nice to do this change, and it was never too late.

Going back to the experiment, we analyzed the data by plotting the points and taking an exponential trendline. We had a nice graph, however we obtained a 10% deviation from the accepted value.

There were some trivial things I learned in this experiment.
1) W/cm^2 is a unit for irradiance and lux is a unit for illuminance (http://www.vernier.com/til/413/)
2) The light sensor we used is optimized for visible light only, much like our eyes.
3) Illuminance is different from light intensity, as well as luminous flux.