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 on April 24, 2018