Be sure to include the uncertainty and units. QUESTION 2: Using the diffraction equation and the slope of your graph, calculate the wavelength of your laser pointer. Print the graph and include it with your Activity Log. Record the slope and intercept (and uncertainties) in Table 4 of your Activity Log. Then double click on the box that appears and in the Standard Deviations section check both the Slope and Intercept. To do so, pull down the Analyze menu and select Linear Fit. Calculate and display the regression line for this data set. Graphical Analysis Launch Graphical Analysis by clicking on the icon in the below. Using the grating equation, calculate the path difference δ for all the angles you just obtained, and record the values in Table 3 of your Activity Log. Using your trigonometry skills, calculate the diffraction angles θ for all the spots you have measured. Record the distances in Table 3 of your Activity Log. Repeat this procedure to obtain the average distances for each of the six higher order spots. Divide this distance by 2 to obtain the average distance, X, between either spot and the centre. Measure the distance D between the two first order bright spots. Zeroth order Note: You should be able to see at least 8 higher order spots on both sides of the central spot.Ĭalculations Remove the screen from the bench and lay it flat on the bench top. Qu ick Tim e™ a n d a TIFF (U n com pressed) decompr essor a r e needed to see th is pictu r e. Have your partner carefully mark the centre positions of at least 6 bright spots on each side of the zeroth order spot. Make a note on the screen as to which spot this is. The spot that appears in the middle is known as the zeroth order. If you don’t check that the laser is passing through the grating. Making Your Mark! Shine the laser through the diffraction grating and make sure you observe a diffraction pattern. Measure the distance between the diffraction grating and the screen and record it along with the associated uncertainty in Table 1 of your Activity Log. Make sure the screen and diffraction grating are parallel by measuring the screen to grating distance on each side of the assembly. Setup: Determining the Wavelength Place the grating and laser assembly approximately 30 cm from the screen. Tape some white paper to the front of your screen. Use the clamps provided to fasten the screen so that it does not move. Place the screen in front of two posts which are screwed into the bench top. This is not simply the number of lines/mm! Position the diffraction grating in the slot in front of the laser. Record the slit spacing written on your diffraction grating in your Activity Log. Setup: Determining the Wavelength Place your laser pointer in the groove in the base. Can you explain their appearance using the grating equation? QUESTION 1: Explain the appearance of the room lights by considering the grating equation. What do you see? Look at the lights in the room through the grating. Part II: The Diffraction Grating What happens when light passes through a diffraction grating? Put the diffraction grating in front of your eye and look around. ![]() Laser pointer Metre sticks CD Diffraction Grating of known slit spacing Mounting assembly Some sheets of white paper Once the wavelength of the laser is known, it will be used to determine the groove spacing of a Compact Disc. ![]() This expression illustrates that constructive interference occurs when the path difference δ is an integer number of wavelengths. Where m is the order number, λ is the wavelength of light, d is the slit spacing of the grating, and θ is the diffracted angle. Part I: Introduction One of the goals in this lab is to use a diffraction grating to determine the wavelength of a laser pointer. Part II: The Diffraction Grating Part III: CD Groove Spacing
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