Laboratory 6 Energy of Light: Finding Planck's Constant Objectives Use LED activation voltages to find the value of h, Plancks constant Calculate the value of h using two different methods . Equipment and Materials MicroLab interface Energy of Light module . Introduction The relationship between energy (E) and frequency (V) of visible light will be examined using an energy of light module. The module works by placing an increasing voltage through a selectable LED. When a high enough voltage is reached, electrons can be excited to the next energy level in the LED material and current will flow through the diode, allowing it to illuminate. The wavelength of the light put off by the LED deter- mines the energy required. A series of voltage measurements at different wavelengths will allow you to determine the value of Planck's constant using the relationship E = hv. Energy of LINE Finding Pandas Constant Laboratory Toothm 7.3.104 HZ Badet Alshammet - 0260517670 Laboratory Nie ID NA 6 w Cw Zac Hartman. Per Not applicable) Daw of Moring Worksheet PART I. QUALITATIVE PROPERTIES OF LIGHT 1. Consider the equation civ. Since is a constant (speed of light, 3.0 x 10 m/s) what happens to the value of when is decreased? When is increased? Explain. 2. Now consider the equation E - lv. Here, bisa constant (Plancks constant, 6.626 X 10 "J.sec. What happens to the Energy (E) when v decreases? When vincreases? When dis decreased, Vincreases, and ter when tither Vincreases i decreuses because cis cehstent, so the Product of them should equal. Thus, as one increases the other one decreased when udecreases the Energy (E) decreases because it is the prodact of hand V. Thus, when u increases & increases because as tent" ause it depends only The high energy is associated with the violet color of the Visible light and has highest ghebes of loommand 43.10" Hz. alowenergy is associated with the red color Se lowest ehere A Foo and 2.3.1 HR 3. What color of visible light is associated with high energy? Low energy? What are their relative values of land v mistry 141 Experimental Chemistry PART II. QUANTITATIVE PROPERTIES OF LIGHT 1. Plug in your Energy of Light module into Port on your MicroLab interface. Tum the interface on (if it's not already) and start the Microlab program. Open a new experiment by clicking on the "Energy of Light Experiment" icon. Select the 470 nm LED with the rotary switch on the module. Make sure the value knob is all the way counterclockwise. 1. Click on the Blue 470 nm" line in the box on the left of the screen. 4. Click on the "Start Graphing" button to begin taking data. 5. Slowly rotate the voltage knob on the module in a clockwise direction. If you look at the screen you will see the blue triangle moving to the left as the voltage in- creases. The current will remain constant until the voltage becomes high enough for electrons to flow through the LED. 6. Continue rotating the voltage knob until you see the current (y-axis value) increase rapidly. At this point you should see that the LED is lit on the module. While looking at the LED from the top, decrease the voltage slowly using the knob until the LED is just starting to produce light. (Your eyes are more sensitive than the ameter measuring the current.) 7. Press the "Mark" button on the module and you should see a dot appear on your graph. This records the activation voltage. 8. If you get a bad mark or a bad set of data, you can select the LED in the software and choose "Erase Data". The program will only erase that LED's data. 9. Sketch your results for your first LED. At what approximate valms did the current begin to show a dramatic increase? At what voltage did your blue LED begin to light? Which of these shopld you use as your activation voltage? Explain. used because it matbes the minimum The 1.6 7 Value Should be Value of energy heeded te light up the LED 10. Your next LED will be at 502 nm. Do you expect the pctivation voltage to be higher 167v.gov or lower for that LED? Explain your reasoning Activation Voltage should be lower because the wavelength is langere 38 Energy of Light Pinding and Constant Laboratory 11. Choose the next LED on the module and in the software and repeat the data gathering steps: 12. The 890m and 940mm LEDs are in the infrared region and you will not be able to see the LED light up visually. If you have a non-iPhone phone, you can watch the LED light up using your camera function. (Phones have an IR filter. For these TWO LEDsyou will need to determine the activation voltage by seeing where the current increases suddenly on the graph. PART III. DATA ANALYSIS 1. Fill in the table below Hint: Use your equations from the first section to find frequency. A must be in meters for this C 3 x 10 m/sec 1 V-1.60218 X 10" Wavelength ml 1/Wavelength im Frequency Iv, 1/wel EIJO Activation TVV KESXlon 4.7B 3.12X31638 1.67 2.68 x 16 219 5.02.10 1.94159 5.18x10'a l.si 2.42Xlah 5.68.16716X155, 2816 1.23 1.41X lot 6.ozilo T.668156 4.488 10y ld3 1,81x10h 601-1671.56X16364.69x1da 1.03 8.80.161.134 163.uixton (1.348154 not lot 1.6x8 (3.14 Aloth 1075 1.2217. 2. Using your data, what geriations can you make about wing and , eheroy dereuses. As frequency decreases, ehergy decreases. 081 to find the value energy (E) on the the yaxis E 30 We focus on PO Box 7520 Tempe, ARE PROSPER Chemistry 141 Experimental Chemistry the percentage eller 4. The first graph is essentially a graph of E - hy with E on the yaxis and on the x-axis. Knowing this, how can you find the value of h? Find the value of h using your method and record here. 5. Calculate the percent error for your value. %error measured value accepted value accepted value X 100 ha emA don't do that 6. The second graph is more difficult to interpret. Open the additional pdf for this lab in D2L and read the section on Analysis and Results to find how to find the value of Planck's constant from your graph. Find the value for for this pond gaph and pepory here. Show your calculations cover their Slopes te meters 7. Calculate and record the percent error for this value of h. 8. Which graph is moye accurate? Why do you think that might be
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