The Critical Angle

LAB 5

Folks,I had corrected the page showing lab 5 Critical Angle so that it reads, water to air, glass to air and glass to water. If you saw the page before I corrected it you might have it backwards. You cannot get a critical angle if you are doing air to water, air to glass and water to glass BECAUSE the medium in which you are in and trying to leave must have a GREATER index than the medium you are trying to go into.The video is flawed!!! The person who made that video did not catch his mistake. That is not me talking. Those videos are made for the course by some person or persons unknown to me. So please take heed what I said above. I will contact IT and Angel Support and report this major error.My apologies for anyone inconvenienced or confused by this matter.

Lab week 5 -  If you skipped ahead prior to week 5 actually starting, you might have found the conditions not allowing you to compute the critical angle. I have fixed the file so that the ray is always presented as going from a higher index to a lower index of refraction. If you just started this lab in week 5 you have no worries otherwise.  EVERYONE needs to understand you are required to do THREE plots using excel (NOT WORD!) I would also suggest you do one Excel file with 3 sheets, one sheet for each case discussed here, and that from your tabular data (which I want to see with the plots!) and your plots you will see where the critical angle occurs. HINT: you may want to go back and refine the increments between where you think the critical angle occurs. For instance, should the angle seem to occur  between 44 and 46 degrees you may want to try making the increments 0.2 degrees, that is up to you to experiment with.   Recall that Excel does not compute in degrees by default. You need to recall the formula context of how to write an angle in Excel. I would suggest you make a few columns first. n1, n2, theta incident (run from 0 to 90 degrees in 2 degree increments), theta refracted degrees (run from 0 to 90 degrees in 2 degree increments), theta refracted (with radian context). you need to use a function like this one, "=ASIN(((Cell#)*SIN(RADIANS(Cell#)))", without the quotes, this is an example of how Excel uses your degree entry and computes the trig function by converting to radians first internally. Do you know what I wrote there? I am writing Snell's Law in Excel vernacular. I wrote what the refracted angle should be as an Arc Sin function. Recall n(1) * sin(incident angle) = n(2) * (refracted angle). So I solved it for the refracted angle, again in the vernacular of Excel. Pay attention to the output. You will see the result become an error (#NUM!). That means you are either at or just passed the incident angle that is the critical angle. (That is all I am going to say about using Excel functions. It is up to you to review how you use Excel as a tool as. You should know how to do this since you had to do this exact type of thing back in Physics I for the projectile motion lab). That means the light ray is not escaping the medium it is in and will reflect back inside. HOLY COW!!!  Did you just see the Law of Reflection come out of the Law of Refraction? That means when Snell's Law fails, reflection takes over.  Think about that. If you have the same angle for incidence and refraction, but you don't get refraction, that means you get reflection. That means Snell's law n(1)*sin i = n(2) sin r is n(1) = n(2).  Of course it is. You never left the medium. VOILA

Lab 5:

Graph 1

c1:

Graph2:

c2:

Graph3:

c3: