PhysicsLAB Lab
A Photoelectric Effect Analogy

It is possible to visualize some of the concepts in the photoelectric effect by using colliding balls to represent scattering particles and obstacles to represent energy thresholds. In order to illustrate the concept in a clearer way, a life-size model of a photon ejecting an electron has been constructed. The model consists of the following:
 
  • An inclined track to roll a metal 1"-diameter metal ball down
  • PVC tubes cut to approximately 7"-lengths with thin rubber bottoms
  • One metal 1"-diameter ball
  • Two collisions ball: plastic, aluminum, brass, or wood
 
Additional equipment needed:
 
  • 3 hot wheel's track sections
  • masking tape
  • meter sticks
  • white target paper with carbon paper to mark impact positions
  • 2 metal stands
  • 2 test-tube clamps
  • 2 c-clamps
  • plumb line
  • triple beam balance
  • protractor
 
         
 
 
Procedure 
 
  1. The collisions balls will be inserted individually into the tube so that they rest against the tube's rubber bottom
  2. The tube is then mounted at the end of the track, with approximately one centimeter of track extending beyond the end of the tube.
 
 
  1. The 1"-diameter metal is placed at various heights along the track and is released to roll down the track and collide with the bottom of the PVC tube
  2. The collision ball resting on the inside of the rubber bottom feels the collision of the metal ball and bounces upwards.
  3. If the collision ball bounces free of the tube, record its impact position on the floor.
 
Masses
 
Record the masses of any two of the following collision balls
 
wooden ball (kg)
plastic ball (kg)
brass ball (kg)
aluminum ball (kg)
 
General Data
 
After each group has built their "photoelectric apparatus" you need to measure the following values:
 
  • Height of table top
  • Angle of PVC tube
  • Length of PVC tube
  • Height of bottom of PVC tube above the table
 
 
height of the table (m)
angle of PVC tube (degrees)
length of PVC tube (m)
height of bottom of PVC tube above table top (m)
 
Experimental Data
 
 
You are to release your metal ball from a minimum of 7 heights, repeating each height two times (or more if your results are inconsistent). Each recorded trial should represent a "good hit."If the collision ball "escapes" from the PVC, record its range. If it leaves the tube but remains on the 1-centimeter lip, record the range as zero. If its doesn't escape at all, record its range as NULL. You should only record one NULL result and perhaps one zero result. The other five heights should have mmeasureable ranges. Repeat with a second type of collision ball.
 
Group I: Collision ball used
 
trial
 
release height
(m)
range
(m)
          
position 1
position 1
position 2
position 2
position 3
position 3
position 4
position 4
position 5
position 5
position 6
position 6
position 7
position 7
 
 
Group II: Collision ball used
 
 
trial
 
release height
(m)
range
(m)
          
position 1
position 1
position 2
position 2
position 3
position 3
position 4
position 4
position 5
position 5
position 6
position 6
position 7
position 7
 
Analysis and Conclusions
 
Once all of your trials have been completed and your ranges measured, you will open the EXCEL file 1-PhotoelectricAnalogy.xls and enter your averages for each trial for each collision ball. Note that there are two worksheets in the workbook.
 
When your spreadsheet is complete, obtain printouts and then answer these conclusions.
 
Which particle does the metal ball represent?
 
What property of the metal ball were you changing by placing it higher or lower on the track?
 

What effect does this represent in the photoelectric effect equation? 

What does the tilted height of the PVC tube represent in the photoelectric effect equation?
 

What property were you changing with the second collision ball?
 

How could you have modeled that metal plate’s surface has many electrons?
 





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