Physics307L:People/Gibson/Notebook/070910

Setting Up

To begin this lab we first observed three pieces of equipment; a voltmeter, a mercury vapor lamp, and the h/e apparatus. Setting this up was quite confusing and both Matt and I had several ways to hook up the voltmeter, but we finally found out how to actually hook it up using the volt cable (red cable and red input) to the positive terminal of the h/e apparatus. The grounding cable (black went from the volt ground to the negative terminal of the h/e apparatus.

Experiment 1 - The Photon Theory of Light

The purpose of this was to determine the stopping voltage (where electrons stop leaving the material due to the photoelectric effect) of the material from the mercury lamps spectrum. In addition to this, we used a transparency filter (100%, 80%, 60%... 20%) and began recording those values. Certain values of wavelength (green, yellow) require a filter to rid the results of surrounding light.

NOTE: DVM reads incorrectly for producing a 0 potential through the h/e apparatus. It reads at a (+) .04V

All measurements are using the first order spectral lines with the Variable transmission filter.

---

    Ultra-violet maxima stopping voltage readings - (NON TRANSMISSION LENS - 2.15)
    2.09V in 3.06 seconds at 100%
    2.09V in 4.89 seconds at 80%
    2.09V in 5.49 seconds at 60%
    2.09V in 6.99 seconds at 40%
    2.09V in 9.69 seconds at 20%

    Violet maxima stopping voltage readings - (NO TRANSMISSION LENS - 1.78)
    Previously we calculated these values:
    1.73V in 5.91 seconds at 100%
    1.73V in 3.83 seconds at 80%
    1.73V in 3.53 seconds at 60%
    1.73V in 4.18 seconds at 40%
    1.73V in 8.70 seconds at 20%
    -These values do not follow a predicted pattern, however we kept the data and recalculated new data.
    NEW VALUES:
    1.74V in 3.63 seconds at 100%
    1.74V in 5.37 seconds at 80%
    1.74V in 5.58 seconds at 60%
    1.74V in 7.71 seconds at 40%
    1.74V in 14.90 seconds at 20%

    Blue maxima stopping voltage readings - (NO TRANSMISSION LENS - 1.57V)
    1.53V 4.71 seconds - new trial 1.97 100%
    1.53V 3.70 seconds - new trial 3.13 80%
    1.54V 2.70 seconds - new trial 4.03 60%
    1.54V 3.50 seconds - new trial 5.76 40%
    1.54V 6.69 seconds - new trial 6.60 20%

    Green maxima stopping voltage readings - (NO TRANSMISSION LENS .91V W/O GREEN FILTER 1.05V)
    0.91V 6.91 seconds at 100%
    0.90V 8.15 seconds at 80%
    0.90V 10.90 seconds at 60%
    0.90V 16.99 seconds at 40%
    0.90V 26.77 seconds at 20%

    Yellow maxima stopping voltage readings - (NO TRANSMISSION LENS .77V W/0 YELLOW FILTER 1.11V)
    0.76V 5.62 seconds at 100%
    0.76V 6.17 seconds at 80%
    0.76V 8.73 seconds at 60%
    0.76V 15.03 seconds at 40%
    0.76V 30.65 seconds at 20%

Experiment #2 : Planks Constant

• for this part we are suppose to once again determine the stopping potential for each color in the mercury spectrum. However we must do this for second order spectral lines also. Doing each of these two things twice to test for reproducibility, and then plot all four sets of data and perform a least squares fit and determine h and Wo. Where Wo is the work function for the cathode inside the h/e apparatus.

   Ultraviolet -1st order             Ultraviolet -2nd order
      - Measurement 1: 2.12V                   - Measurement 1: 2.10V
      - Measurement 2: 2.12V                   - Measurement 2: 2.10V
   Violet -1st order                  Violet -2nd order
      - Measurement 1: 1.76V                   - Measurement 1: 1.76V
      - Measurement 2: 1.77V                   - Measurement 2: 1.76V
   Blue -1st order                    Blue -2nd order
      - Measurement 1: 1.56V                   - Measurement 1: 1.57V
      - Measurement 2: 1.55V                   - Measurement 2: 1.58V
   Yellow -1sr order                  Yellow -2nd order
      - Measurement 1: 0.77V                   - Measurement 1: 0.78V
      - Measurement 2: 0.76V                   - Measurement 2: 0.78V
   Green -1st order                   Green -2nd order
      - Measurement 1: 0.91V                   - Measurement 1: 1.10V
      - Measurement 2: 0.90V                   - Measurement 2: 1.10V

In our search for determining how to figure out the frequency order of the color spectrum we (Matt G and I) found a wiki website: Color spectrum and for EM spectrum where we obtained most of our formulas and the actual value of Planck's constant.

[math]\displaystyle{ \lambda = \frac{c}{f} \,\! }[/math]

and

[math]\displaystyle{ E=hf \,\! }[/math]

or

[math]\displaystyle{ E=\frac{hc}{\lambda} \,\! }[/math]

Data Analysis

This section is made to analyze the four graphs from experiment 2.

Website for Stopping Potential relation to KE of the electron