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phy124:lab_7 [2010/03/29 23:16]
mdawber
phy124:lab_7 [2010/04/03 11:58] (current)
mdawber
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+<​html><​STYLE>​ #​jsMath_Warning {display: none} </​STYLE></​html>​
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====== PHY124 Lab 7 - Reflection, Refraction and Images ====== ====== PHY124 Lab 7 - Reflection, Refraction and Images ======

There are two parts to this lab which can be done in either order In Part I you will  study the Laws of Reflection and Refraction, measure the index of refraction of glass and observe dispersion. In Part II you investigate images produced by lenses. There are two parts to this lab which can be done in either order In Part I you will  study the Laws of Reflection and Refraction, measure the index of refraction of glass and observe dispersion. In Part II you investigate images produced by lenses.
+
+[[http://​www.ic.sunysb.edu/​Class/​phy122ps/​labs/​dokuwiki/​pdfs/​124lab7worksheet.pdf|Important! You need to print out the 4 page worksheet you find by clicking on this link and bring it with you to your lab session.]]
+
+If you need the .pdf version of these instructions you can get them [[http://​www.ic.sunysb.edu/​Class/​phy122ps/​labs/​dokuwiki/​pdfs/​phy124lab7.pdf|here]].
+
+
+===== Video =====
+<​flashplayer width=640 height=480>​file=http://​www.ic.sunysb.edu/​Class/​phy122ps/​labs/​phy122vid/​phy124lab7.flv</​flashplayer>​

===== Part I ===== ===== Part I =====
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* Triangular prism   * Triangular prism

-{{124l7fig1.jpg}}+{{124l7fig1.jpg}} ​
+\\ Fig1
==== The laws of reflection and refraction ==== ==== The laws of reflection and refraction ====

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===== Part II ===== ===== Part II =====
-
==== Equipment ==== ==== Equipment ====
* 1 “Optical Bench: a rail to mount the holders of lenses/​screen on   * 1 “Optical Bench: a rail to mount the holders of lenses/​screen on
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* 1 Lamp with arrow (our object to be imaged)   * 1 Lamp with arrow (our object to be imaged)

+Verify that you have the correct lens mounted before you start measuring! The lenses are marked at the bottom of the shaft of the lens holder:
+#3: 10 cm diverging lens
+#4:   5 cm converging lens
+
+{{124l7fig3.jpg?​600}}
+\\ Fig3
+
+{{124l7fig4.jpg}} ​
+\\ Fig4
+
+==== The imaging law for lenses ====
+
+The purpose of this part is to study images made by lenses and to verify the imaging laws for lenses.
+
+The imaging law for the lenses relates the distances from the object (o) and the image (i) from the lens to the focal length (f) of the lens.  This relationship is given in Ch22 sheet 20'.
+
+<WRAP column 35%>\\
+</​WRAP>​
+<WRAP column 45%>
+$\frac{1}{o}+\frac{1}{i}=\frac{1}{f}$
+</​WRAP>​
+<WRAP column 10%>
+(7.3)
+</​WRAP>​
+\\
+
+The equation for the magnification m of lenses is given in Ch22 sheet 20.
+
+<WRAP column 35%>\\
+</​WRAP>​
+<WRAP column 45%>
+$m=\frac{-i}{o}$
+</​WRAP>​
+<WRAP column 10%>
+(7.4)
+</​WRAP>​
+\\
+
+You will use equation (7.3) and equation (7.4) to measure the focal length and the magnification of a lens with an expected focal length of 5 cm.
+==== Procedure ====
+
+Make sure that the lam and the painted arrow (the “object”) are placed at one end of the optical bench, with the arrow a few cm in front of the lamp and pointing upward. ​ The arrow and lamp will remain in that position for this part of the experiment. ​ The screen and the lenses will be moved. You will observe two images, one magnified, the other demagnified,​ depending on the position of your lens.
+
+=== Focal length and Magnification for the 5 cm Converging Lens:​Quantitative ===
+
+
+Mount the 5 cm (#4) lens in the lens holder. Mount the screen into a holder and place it at ~ 30 cm from the object. Place the lens between the screen (“image”) and the object as close to the object as possible. Move the lens towards the screen until you can see a sharp image on the screen. ​ First, observe the size and orientation of the object and of the image. ​ Record them into your Execution Sheet. ​ Next, locate the positions of the image, lens and object and record them in your Execution Sheet. Your dominant error in the locations will be the error of the lens position. ​
+
+Note that the lens is not centered on the lens holder but offset by 0.6 cm. Make sure you note the orientation of the lens. If it is oriented as shown in Fig. 4, so that the lens is closer to the screen, you must increase the lens position by 0.6 cm. If the lens is further from the screen you must decrease the lens position by 0.6 cm.  Assume an error in the lens position of 0.2 cm. Estimate the errors of the image and object size ($h_{i}$ and $h_{o}$) as well.
+
+The important quantities you obtain from these positions are the distance from the lens to the image and the lens to the object and the errors associated with these distances.
+
+On the graph paper on your worksheet make a drawing – to scale (1 square = 1cm in the horizontal direction, 1 square = 0.25 cm in the vertical direction) – containing object and image arrows and the lens with object and image distance and the nominal focal length of 5 cm. Reconstruct the image with the two principal rays (see Ch22 sheet 20).
+
+Use equation (7.3) to calculate the focal length f of the lens and its error from your measured o and i values.
+
+To calculate the error of f simply assume that the object (o) and image (i) distance have the same absolute error, which is given by the dominant absolute error of the lens position (discussed above). ​ Use the fact that the reciprocals 1/i, 1/o and 1/f  have the same relative errors as i, o and f, and propagate the absolute errors of the reciprocals according to expression (E.6) in Error and Uncertainty. ​ (Also, remember your lab prep exercise.)
+
+Compare your obtained value of f with the nominal value of 5 cm, is it consistent?
+
+Find the magnification from the measured heights of the image and object using $m=h_{i}/​h_{o}$.
+
+Calculate the error in the measured magnification from the errors in $h_{i}$ and $h_{o}$ using equation (E.7) in Error and Uncertainty.  ​
+
+Calculate the magnification from the measured image and object distances using equation (7.4).  ​
+
+Calculate the error in this calculated value for the magnification from the errors in i and o using equation (E.7) in Error and Uncertainty.  ​
+
+Are the two values obtained for the magnification consistent with each other?
+
+Move the lens to another position, closer to the screen, where you get a sharp image of a different size. Record the same data for that position. No errors are needed here.

+On the graph paper on your worksheet make a drawing – to scale as before – containing object and image arrows and the lens with object and image distance and the nominal focal length of 5 cm. Reconstruct in your drawing the image with the two principal rays (see Ch22 sheet 20). Get the measured magnification $m=h_{i}/​h_{o}$ ​ and compare it to the value obtained for your 1st lens position. ​

+=== Image and Magnification for the 10 cm Diverging Lens: Qualitative only ===

+Mount the 10 cm (#3) diverging lens in the lens holder. Place the lens at as close as possible to the object. Try to make an image on the screen by moving the lens and screen around (verify that you don’t in fact produce an image on the screen). Remove the screen and place your eye close to the lens so that you can observe the image the lens produces from the object. Describe on your worksheet whether the image (what you see) appears upright/​inverted,​ magnified/​demagnified with respect to the original object

+Slide the lens away from the object and, keeping your eye close to the lens, state on your worksheet whether the properties of the image, apart from the size, change as you increase the distance of the lens from the object., i.e. is the image for any object distance upright/​inverted,​ magnified/​demagnified. Is the image real or virtual? ​