PIRA 7A10.10 - Photoelectric Effect: Photoelectric Effect in Zinc
Photo Shows the Demonstration Set Up for a Humid Day - rod and fur are missing.
Instructions and Notes:
- A mercury vapor lamp shines on a negatively charged zinc, which is mounted to an electroscope.
- The zinc plate must be freshly sanded by the demo staff prior to the class break
- Use a PVC rod rubbed with rabbit fur to charge the zinc plate.
- An optional table lamp can be provided with the Photoelectric effect by also requesting demo no. 4D20.10
Note: This electrostatic demonstration is performed in open air - Waiting until the middle or end of class on a humid day will be problematic.
To perform the demonstration:
- Rub the PVC pipe in the rabbit pelt and touch the PVC pipe to the top of the zinc plate
- The UV light has a removable red colored gel filter
- Once the filter is removed, the charge registered by the electroscope decreases
With regards to using the visible spectrum of light - add Demo #. 4D20.10, the Crooke's Radiometer to the Photoelectric Effect Demo.
- The photons in the visible light spectrum do not reach the threshold needed for the charged Zinc to eject electrons.
The Photo Below shows the Demonstration Set Up for a Dry, Winter Day .
Option 2: alternative setup which uses an open air electroscope, but...
- The type of electroscope provided with Option 2 needs to be used at or near the start of class - or - not at all.
- An open air electroscope will not function after about 5 or 10 minutes of lecture in the Texas humidity
- The advantage of the open air electroscope is it allows most of the students in the room to view the electroscope needle.
- To request option 2 - type a short request in the "Notes field" when ordering, "Please provide Option 2 with the PE demo."
The 4 minute video below is intended for staff instructional use.
Last Updated 04/2018 - University of Texas at Austin Physics Department
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