# User:Joseph Frye/Notebook/Physics Junior Lab 307L/Plank

Steve Koch 04:48, 21 December 2010 (EST):Good primary notebook as far as methods for data collection. More description of analysis needed.

## Plank's Constant

This lab was performed in the junior laboratory in the UNM physics building on November 22nd with Derick Boeck. Following the procedure outlined in Dr. Gold's lab manual

## Setup and Equipment

• h/e apparatus (in the junior lab)
• mercury lamp
• prism
• yellow filter
• green filter
• intensity filter
• digital multimeter

The equipment set up for this lab was simple because of the fact that the h/e apparatus, the mercury lamp, and the prism are all in the same unit. Set up involved plugging in the lamp and connecting the DMM to the h/e apparatus.

## Procedure and Data

Experiment 1

SJK 04:43, 21 December 2010 (EST)
04:43, 21 December 2010 (EST)
Kudos to you for realizing that this is not a linear relationship! It's not exponential either--actually more reciprocal: the rate of charging should be proportional to intensity. The rate is reciprocal of time.

The lab manual details two experiments for this lab. The first is to measure the stopping potential of both yellow and green light emitted from a mercury lamp. Then we measure the time it takes for the equipment to build to that stable voltage after resetting the charge. We measure the time with different filters placed over the opening. The filters effectively vary the intensity of the incoming light. The filters are labeled as 100%, 80%, 60%, 40%, and 20%. By measuring the time it takes for each intensity to build to the stopping potential, we hope to establish a relationship between that time and the intensity. The idea is that if the particle theory of light is true then the stopping potential will be the same for each intensity, but the time will increase as the intensity decreases.

Experiment 2

The second experiment is to measure the stopping potential of different wavelengths of light in order to find a relationship between the frequency of light and the energy of a photon. We then will use this data to calculate Plank's constant (h). Plank theorized a relationship between the energy of a photon and it's frequency. E=v*h where E can be calculated from the stopping potential in our experiment, and the frequency v is calculated from the known wavelengths of the mercury spectrum.

Data

Experiment 1:

after graphing the data from the first experiment we found that there does seem to be a relationship between intensity of light and the time it takes to reach the stopping potential. The intensity did not affect the stopping potential itself suggesting that the photon theory of light is correct.

Experiment 2:

We measured the stopping potential of 5 wavelengths of mercury in the 1st order spectrum and we also measured the same 5 in the 2nd order spectrum. we measure each twice our data and the analysis can be found in the spreadsheet.

Our data and analysis: Image:PlanksconstantFRYE.xls

## Results

1st Order Trial 1 h=8.39E-034

1st Order Trial 2 h=8.17E-034

2nd Order Trial 1 h=6.95E-034

2nd Order Trial 2 h=6.92E-034

SJK 04:45, 21 December 2010 (EST)
04:45, 21 December 2010 (EST)
Is it appropriate to average these, since they clearly have differing parent means?

Average h: 7.61E-034

Standard Dev: 7.81E-035

Accepted value of h: 6.63E-034

relative error: 1.48E-001

SEM: 3.91E-035

I calculated Plank's constant to be:

h = 7.61(39)*10^(-34) (kg*m^2)/s