PHOTOELECTRIC EFFECT

In this excercise we measure Plank's constant h and the work function of an unknown metal.

eVs = hf - W

(1) Turn the Hg lamp on and let it warm up for 15 minutes before taking any data. .

(2) Do not stare in to the Hg source, the UV can be harmful to your eyes.

(3) Place each fillter carefully over the window opening and adjust the stopping voltage up until the current drops to near zero. (You will notice I moving between + and - picoamps zero).

(4) Fill in the following chart.

 Wavelength  Color  Stopping Voltage
 440 nm  BLUE 1.42 V
 535 nm  GREEN  0.73 V
 650 nm  RED  0.34V

(5) For your home asignment graph the frequency vs stopping voltage as discussed in class. Find the slope and intercept of your data and record the values in the chart.

 Slope  
 Intercept  

(6) Determine Planck's constant and the work function of the metal cathode. Record thes

 h  
 W  

(7) Compare your answer to the accepted value for Planck's constant h and report this as a %Accuracy = Dh/h

 Dh/h =

(8) Can you identify the likely metal photocathode from the work function?

 

(9) Attach your graph and a sheet of calculations to this page for turning in.