Photoelectric Effect

Produced by the National STEM Learning Centre and the Institute of Physics, this video demonstrates how to use a gold-leaf electroscope, zinc plate and an ultraviolet light source. The zinc plate is placed onto the top of the electroscope and it is given a negative charge.

The electroscope can be discharged when ultraviolet light is shone onto the zinc plate. This is due to the UV light photons causing the discharge of electrons from the zinc plate.

The photoelectric effect helps to illustrate the wave-particle duality of light.

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Stuart Billington

An excellent video -- very efficient and clear commentary. Thanks!

Paula Rowe

The information about cleaning the zinc with wire wool may have saved us the price of a new (£99) UV lamp.  Thanks.


Help, please....How powerful does the UV light have to be? We will have to buy one.....will a cheapish torch do??

Adam Little

Demonstrations usually need a Class 2 laser which is a maximum of 0.99mW.

CLEAPSS guidance on this and UV sources can be found here:


Hi -
I cannot seem to get the photoelectric effect to work properly with the apparatus I have.
At our school we have 3 different types of UV lights and while the lights work, I am not seeing any movement of the gold leaf when the UV light is passed near the zinc plate.
What could be the issue? I have cleaned the zinc plate over and over with wire wool, and I have the negative (black) terminal of the EHT supply negatively charging the gold leaf electroscope.

Many thanks