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Preparing for the lab:
We will be doing a substantially modified version of "Lab 40" in the lab manual. About the only thing that is the same is the theory about the law of refraction that is common to both labs.
Answer the pre-lab questions on LON-CAPA after reading the background information on pages 401 to 402 in the lab manual.
The procedure, data tables, and post-lab questions are all given on a handout. The handout also emphasizes the basic principles of safety when working with lasers, points I will elaborate on at the start of the lab.
pdf of first 3 pages of the handout.
The full handout with data table and questions will be available in the lab.
The main principle of safety around equipment like the lab lasers we use is the same as for guns: You should treat every gun as if it were loaded, even if you unloaded it yourself; you should treat every laser as if it were dangerous even if you have checked the label stating that its output is in the "safe" region below 1 mW. You want to get in the habit of working with care so that skill will be automatic if you are working with lasers that are more hazardous. My favorite summary of the issue is given on an unofficial warning sign in a lab:
Do not look into laser with remaining good eye.
This lab probably uses the most primitive tools (apart from a
pretty good laser) of all of the experiments done this semester:
The way this will look when doing the first part of the
experiment (measurement of the index of refraction of water
and verification of Snell's Law) is diagrammed below:
The case in this diagram is for the first observation, which will be for the largest angle to be measured. The other positions should be (roughly) equally spaced between this angle and zero degrees.
We will also look at total internal reflection during this lab. I will show you how to use water to make a "light pipe", since this is not a demo we can do very easily in the classroom, and you will estimate the critical angle for comparison to the one you calculate from your data.
Contact me if you have any questions.