Formal Report rough draft

Abstract

This project was conducted in order to find a value for Planck's constant, one of the most fundamental constants, experimentally. The value I calculated from my experimental data was 6.99768E-34 +/- 7.43E-36 J*s. Compared to the standardly accepted value of h = 6.626068 E-34 J*s. The value I calculated was about 5% off of the expected value of the constant, given the limits of the testing apparatus that was used is quite encouraging. This was accomplished by allowing a mercury light spectrum to be incident on a photoelectric material and measuring the stopping potential for various wavelengths of light, this data paired with the work function equation enable me to calculate a value for h.

Introduction

This experiment was designed to find Planck's constant, one of the fundamental constants of nature. The relationship between the energy of a photon and the frequency of its electromagnetic wave was one of the truly great discoveries in science. Work that was later expanded on by Einstein's further investigation of the photoelectric effect¹ as it applied to electrons being freed from matter by incident light and De Broglie's work² that expanded the relationship between energy and the quantum wavelength to all particles.

It was however, Planck's work, in looking at Black body radiation that led him to treat energy in relation to frequency as a discrete value or quantity instead of a continuous function. This work was the beginning of quantum physics³. Even though Planck had made this quantum leap because the math worked out, other physicists continued this work and showed there was a real relationship between energy and frequency.

Using the experimental procedure detailed in my lab notebook [[1]] from Dr. Gold's manual⁴, i was able to calculate a value for h.

Procedure

The experiment was setup so that light from a mercury lamp would pass through a diffracting prism creating a spectrum of light, this light was focused on a photosensitive material with a very low work function. Using five distinct wavelengths of light we were able to measure the stopping potential required to offset the energy of the ejected photons in the material (Table 1).

Color Wavelength(nm) Frequency(hz) UV 365.483 8.20264e14 Violet 404.656 7.40858e14 Blue 435.835 6.87858e14 Green 546.074 5.48996e14 Yellow 578.000 5.18672e14

References

1. On a Heuristic Viewpoint Concerning the Production and Transformation of Light, Albert Einstein
2. Selected Papers on Wave Mechanics by L. de Broglie
3. J Franck, Max Planck, Science 107 (1948), 534-537
4. Dr. Gold's manual for experimental physics