Photoelectric Effect
Show the emission of electrons from metals
Materials
Where to Find
Both Electroscopes
Static Electricity Kit
UV Lamp
Shelf 1D
Shelf 3E
Drawer T3
Set Up
Retrieve both of the electroscopes. One has a Zn strip attached and
the other has a Mg ribbon in a lightning bolt shape. Only give them the fur
and plastic rod, this charges the electroscope by adding electrons. The glass
rod will not work because it charges the electroscope by removing electrons
(it creates positive static charge).
Safety
UV short wavelength can be very hazardous. Do not allow it to be
shone into eyes.
Professor/Lecturer
Chemistry
This demonstrates the photoelectric effect. In the photoelectric effect,
electrons are emitted from matter (metals and non-metallic solids, liquids or
gases) as a consequence of their absorption of energy from electromagnetic
radiation of very short wavelength, such as visible or ultraviolet light.
Electrons emitted in this manner may be referred to as "photoelectrons."
The work function is related to the
amount of energy required to eject
electrons from a material. The
work functions for Mg and Zn
translate to 337 nm and 288 nm
respectively.
It is important to note that the material must first be charged with an excess
of electrons because otherwise the ejected electrons will immediately jump
back onto the metals.
Presentation
Charge up the plastic rod with the fur by rubbing the two together.
Use the rod to charge the metals on the electroscopes by sliding the rod
across the surface of the metal. The needle on the electroscope should rotate
clockwise. Turn on the UV lamp by flipping the switch and then holding
down the short wave button and releasing. Shine the UV lamp onto the
metals and watch the needle drops back down. Be careful not to touch the
lamp to the electroscope because the effect will be ruined since the electrons
are transferred to the lamp itself.
Misc. notes/Performance
Search Items
Photoelectric Effect
Electroscope
Light
Electrons
UV Lamp
Wavelength
Suitable for Recitation
Reference
Wikipedia.