Group4_8_ch27-32

=__**Lab: Atomic Spectra**__= Group: Allison Irwin & Erica Levine 3/20/12


 * PreLab:**
 * 1) The objective is stated in the title. What is your hypothesis?
 * By finding the emitted wavelengths of the visible spectra of each element, we will be able to construct an energy level diagram. We will use a diffraction grating in order to see the visible spectra of each element. Using a meter stick we will find the lengths that should correspond with the wavelengths using the equation asin(theta)=mλ.
 * 1) What is the rationale for your hypothesis?
 * Using the equation asin(theta)=mλ we can use our length measurements to find an experimental emitted wavelength. This wavelength will be used to calculate the energy levels and produce the energy level diagram.
 * 1) How do you think you might test your hypothesis?
 * We will view the visible spectra of each element through a diffraction grating. We then use a meter stick to measure the position of the lines produced. Again, using the equation asin(theta)=mλ we can find the experimental wavelength.
 * 1) Read through the procedure notes. Make any tables in order to organize your data and calculations.
 * See data tables produced below.
 * 1) What is a continuous spectrum? A discrete spectrum? What type of light produces each?
 * A continuous spectrum is a complete, uninterrupted spectrum. It shows all wavelengths of visible light. White light creates a continuous spectrum. A discrete spectrum is an emission or absorption spectrum for which there is only an integer number of intensities. Each element produces a unique discrete spectrum.
 * 1) Record estimated wavelengths and colors for the emission lines for Hydrogen, Helium, and Mercury.
 * Hydrogen: 434 (Violet), 486 (Blue), 656 (Red)
 * Helium: 389 (Violet), 464 (Blue), 541 (Yellow), 589 (Orange), 668 (Red), 707 (Red)
 * Mercury: 405 (Violet), 435 (Blue), 545 (Green), 575 (Green), 615 (Orange), 690 (Red)
 * 1) See the images of the emission spectra.
 * [[image:Screen_shot_2012-03-25_at_11.50.51_AM.png width="639" height="293"]]
 * Objective:** To measure the wavelengths of light emitted from several different atoms with high accuracy, and then construct an electron energy level diagram.


 * Hypothesis:** By finding the emitted wavelengths of the visible spectra of each element, we will be able to construct an energy level diagram. We will use a diffraction grating in order to see the visible spectra of each element. Using a meter stick we will find the lengths that should correspond with the wavelengths using the equation asin(theta)=mλ.


 * Methods & Materials:** In order to start the experiment, we needed to determine the lines per millimeter of the diffraction grating. We did this by taping the diffraction grating to an empty lens holder, and putting it at the 0cm mark on the optics bench. We then placed an optics bench at a set distance from the empty lens holder, and used this screen to project the diffraction pattern on to. Then, using a clamp and a ring stand, we shone a laser pointer with known wavelength through the diffraction grating to produce a diffraction grating on the white screen. We used a pencil and paper to trace the diffraction pattern, and a ruler to measure the distances of multiple fringes. After obtaining this information, we were able to use the equation [[image:Screen_shot_2012-03-25_at_2.27.13_PM.png]]to solve for the number of lines per millimeter of the diffraction grating.

We began this experiment by blocking all incoming light from the classroom. We taped paper of all windows to block out natural light, and shut the lights in the room. We then placed a diffraction grating at one end of the optics bench, across from a spectral tube power supply at the other end of the bench. On the top of the power supply, we taped a ruler stick on order to determine the lengths of the diffraction pattern. Next, we placed the respective emission tube (hydrogen, helium, or mercury) into the power supply. One person in the group looked through the diffraction grating to determine the location of the emission wavelengths. While this person pointed at the specific location on a meter stick using a laser pointer, another person read and recorded the y-distance. We then performed the same procedure for all three emission tubes, and the incandescent light bulb. After obtaining y distances, we will be able to determine the different wavelengths on the emissions spectrum using the equation.


 * Data:**
 * Analysis:**

1. Calculate the wavelengths of hydrogen, helium, and mercury and evaluate your results. View table above. All results were fairly accurate, with our highest percent error being 2.15.

2. Use these wavelengths of the emitted photons to draw an energy level diagram for each atom. This must include quantum numbers, the transitions, associated energies, and write the color of the observed line next to its transition on your energy level diagram.

3. Determine the wavelength corresponding to the various points in the spectrum that were located on the continuous spectrum. View table above. All wavelengths calculated in this experiment were fairly close to the known wavelengths looked up on the internet.


 * Calculations:**
 * Discussion Questions:**

1. If the grating actually had more lines/mm than you calculated in Part I, what effect would that have on the calculated wavelenghts? Would the results be better or worse? Based on the equation when the diffraction grating is increased, the wavelength is also increased. This would create larger error because the fringes not be located as far apart as they should have been when calculating them based on the real lines/mm.

2. A diffraction grating with d = 2000 nm is used with a mercury discharge tube. At what angle will the first-order blue-green wavelength of mercury appear? What others can be seen, and at what angle will they appear? If the distance between the grating and the screen is 50.0 cm, at what distance from the center will the first-order image for blue wavelength appear? Show your work.

3. In the continuous spectrum what is the range of yellow wavelengths? Orange? Do these agree with known values? What is the middle of the visible spectrum according to your measured values of the range of the visible spectrum? The range of yellow and orange wavelengths is approximately from 580 nm to 650 nm. These values do agree with theoretical values. The middle of the visible spectrum according to measured results is approximately 550 to 650 nm. This is where we found orange and yellow wavelengths to be located on the continuous spectrum.


 * Conclusion:**

After completing this experiment, we can conclude that our hypothesis was correct. Using the y-disatnces for the different wavelengths on the emission spectrum, we were able to fairly accurately predict the wavelengths for each emission tube. We did so by using the equation. Our results proved to be very precise, with our highest percent error amounting to 2.15%. Although our results were fairly precise and accurate, there was room for error in the experimental setup. Firstly, it was possible that we calibrated the diffraction grating wrong, and this would cause more error in our calculation of wavelength. Secondly, there was a significant possibility for human error in this experiment. Not only may the person looking through the diffraction grating have located the y-distance incorrectly by a few millimeters, but also the person reading the y-distances may have misinterpreted what the first person was saying, and recorded the y-distance incorrectly. In the future, error could be decreased by using a diffraction grating with a known definite lines/cm and by finding a more precise way to measure y distances. This experiment deals with very prominent research in the field of atomic/modern physics. The results we obtained further validate theories that modern physicists are studying every day.