phy124lab6 - phy124:lab_6[Stony Brook Physics for Life...

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PHY 124 Lab 6- Interference and Diffraction Important! You need to print out the 3 page worksheet you find by clicking on this link and bring it with you to your lab session. [http://www.ic.sunysb.edu/Class/phy122ps/labs/dokuwiki/pdfs/124lab6worksheet.pdf] If you need the .pdf version of these instructions you can get them here [http://www.ic.sunysb.edu/Class /phy122ps/labs/dokuwiki/pdfs/phy124lab6.pdf] . Goals The purpose of this laboratory is to study the phenomena of diffraction and interference. In Part I, you will observe the diffraction of light by a human hair (similar to the diffraction on a narrow slit), and in Part II, both interference and diffraction of light by various types of slit arrangements. You can do either Part I or Part II first. Part I - Diffraction of monochromatic coherent laser light by a human hair. In Part I, you will observe the diffraction of light by a human hair (similar to the diffraction on a narrow slit), calculate the hair diameter from your observed diffraction pattern and compare it to a measurement done with a micrometer. Equipment for Part I Helium-Neon Laser with a wavelength of 632.8 nm. Slide Frame to mount the hair. phy124:lab_6 [Stony Brook Physics for Life Sciences] http://www.ic.sunysb.edu/Class/phy122ps/labs/dokuwiki/doku.php?id=p... 1 of 6 3/1/2010 4:41 PM
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Paper to display the diffraction pattern on the wall. Masking tape to record the pattern. Ruler Micrometer Reading the micrometer A micrometer can be used to measure very small distances and diameters. Each division on the knob of the micrometer represents 10 μ m, or 0.01 mm. Each division along the handle represents 0.50 mm. When measuring an object, turn the knob until the micrometer is fitted around the object. Then read the number of lines visible on the long part of the handle. This is how many half mm you have. Then, find which marking on the knob lines up with the center of the line on the handle. Multiply this number by 0.01 to get the amount in mm. Then add it to the number of half mm to get your reading. You can consider the measurement error on this device to be equal to one of the divisions on the knob (i.e 10 μ m) Example: You measure the diameter on a pencil. After fitting the micrometer around the pencil you see that there are 12 lines visible on the long part of the handle, which gives a value of 6mm. Then on the knob you find that the 45 mark lines up with the line going down the handle. Multiplying 45 by 0.01 gives 0.45 mm. Adding this to the first number gives you a diameter of 6.45±0.01 mm for the pencil. Measurement of the hair diameter with a micro-meter First, you will determine the zero diameter reading so you have a clear reference point when measuring the diameter of the hair. Close the micro-meter down without the hair and close the micrometer by applying about the same force you will use later when you are measuring the hair. (The micrometer will show different “zero” readings whether you close it gently or with a large force). What value do you read off of the micrometer? This will be your zero value. When measuring the diameter of
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