1LAB #4: Fun with Light and LasersPhysics 2020, Spring 2004For quite some time, scientists believed that light was composed of tiny particles thatcarried energy. It wasn’t until the early 19th century that people started to view light as awave instead of a constant streem of mysterious particles. In this lab, we’ll explore someof these early experiements that convinced scientists of the wave-properties of light, andhow they can be useful.PRELAB QUESTIONS:0) Read chapter 24 of your text.1) Pick some distant object that you have trouble seeing (this could be a poster on awall, a tree outside your window, etc.). If you wear glasses or contacts, take them offfor this exercise. Make a small hole using your index finger & thumb on one hand andthe tip of your index finge of your other hand. Look at the distant object through thissmall hole. Vary the size of the hole with your fingers and see how your view of theobject changes. What happens, and why do you think this happens?2) On p. 729 in your text, Fig. 24-10 shows the intensity pattern from interference on adistant screen produced by light going through a screen with a double slit. Supposethat a single change were made to this configuration. In each case, determine howthe resulting intensity pattern would change (draw a picture and describe how thepattern changes):A. The width of each slit is decreased (while keeping the distance between the slitsconstant)B. The distance between the slits is increased (while keeping the width of the slitsconstant)C. The screen is moved closer to the double slitsD. The wavelength of the incoming light is decreasedPRECAUTIONS & NOTES:1) Do not look into the laser beam.2) Do not move the laser.3) Do not put your head near the laser beam.4) Last but not least, do not look into the laser beam.PART I: Interference From a Double Slit ExperimentBefore you begin taking any data or observations, play around with the equipment inorder to get a feel of how you set things up and what kind of light patterns the variousslits produce.2Now go back to your predictions you made inpre-lab question #2. Make sure all your labmates agree on what should happen and why.With the availble equipment you have,determine which predictions you can test, andwhich ones you cannot. For the changes thatyou can make, set up an experiment to testthese changes. Record in your lab notebook apicture of the setup, what you did, how youdid it and what the results were. If any ofyour predictions are incorrect, you’ll have todetermine if your experiment or your originalprediction itself is wrong.The diagram on the left is a picture of themask containing all the slits that you will usefor this experiement. The mask consists of anopaque photographic negative, containingseveral single, double, and multiple slits. Thisparticular plate is often called a Cornell Plate, since apertures of this kind where first usedat Cornell University. Next to each set of slits, you will see 3 numbers. The top numberindicates the number of slits, the middle number is the width of the slit(s) and the bottomnumber is the distance between the slits (in millimeters).PART III: Interference and Diffraction CombinedSo far, you have learned what an interference pattern looks like and what a diffractionpattern looks like. The diffraction pattern arises because light is passing through a singlenarrow slit. For the interference pattern, we also have light passing through narrow slits.So, shouldn’t we get some sort of diffraction effect with a double slit, in addition to theinterference effect?This is the question you’ll be addressing in part III of the lab. Here are some things to getyou started:A. Use the single (D=0.107 mm) slit to create a patten on the screen. Take noteof the bright and dark spots from this pattern.B. Now compare that pattern to the one produced by the the double slits (D=0.10mm, d=0.175 mm). What are the similarities and differences between the twodifferent patterns? Do the two have anything in common? Again, trace out afew diagrams of the patterns so that you can compare them. (Notice that boththe single slit and the double slits all have the same slit width, D.)C. After you feel comfortable with parts A and B, compare the single slit (D=0.345mm) to the double slit (D=0.10 mm, d=0.35 mm) pattern. Again, what are thesimilarities and differences between the two patterns?D. Can you say anything in general about what the intensity pattern will look likefor a double slit? (i.e., where will the bright and dark spots be?)1151130217531374120101.430.7550.3450.1950.1080.050.050.010.0270.0440.050.050.050.050.05_ 0.1760.0880.0340.0660.088 _0.1320.1320.1320.132122220.1070.100.100.100.100.1750.350.701.40 _3PART IV: Measuring the Wavelength of LightThe laser you are using is a He-Ne laser (He-Ne stands for helium-neon, which are thetwo elements inside a glass tube that makes up the heart of your laser). We know thelaser light is red, and that the light is monochromatic (meaning only one wavelength isproduced). But what is this wavelength? Figure out a way to measure the wavelength ofthe light from your laser using all the lab equipment you have. Once you obtain ananswer, make sure it makes sense.It’s your lab group vs. the rest of the class! The group with the closest answer to theactual value will receive a secret door
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