Investigating a Light Reflection Experiment

[Mene]

I'm doing an response on a little experiment done in class. I'm having trouble understanding some parts. If someone could reply to the information below, it would really be appreciated.

A large beaker is filled with water, it is covered on the outside by construction paper (any coulour you like!) except the constrution paper has a rentangular opening cut out around the bottom of the beaker to allow light to neter. A Erlenmeyer flask is filled with marbles and water is added to top the flask. The flask is shut with a stopper and placed into the large beaker (the water in the large beaker covers the flask). When looking at the beaker from up top the marbles in the flask can not be seen. If i am to place an object (like my finger) out side, infront of the rectangular paper, it can be seen on the flask. If any clarification is need please ask, I would appreciate it if I can get a reply by sunday night!

P.S. My knowledge only goes as far Total Internal Reflection and Critical Angle. I know that the angle at which the the light is reflected back to the eye is due to partial reflection and the incident angle being greater then the critical angle. Thanks in advance.

 

[Valerie Park]

In this experiment, total internal reflection is occurring. The light comes in through the rectangular opening and is reflected off of the water inside the beaker. This causes the light to be refracted inside the flask, which has a higher refractive index than the air outside the beaker, so that the light is reflected back out of the flask and can be seen by the observer. The angle at which this happens is known as the critical angle, which is determined by the difference in the refractive indices of the two materials (in this case, air and water). If the incident angle is greater than the critical angle, then the light is totally internally reflected and cannot escape the flask. Thus, when you put your finger in front of the rectangular paper, it can be seen on the flask because the incident angle is greater than the critical angle, allowing the light to escape the flask.