The Photoelectric Effect Flashcards
Describe the Photoelectric effect:
If an EM wave with high enough frequency is shone onto the surface of a metal, electrons will be instantaneously emitted.
What frequency range usually causes the Photoelectric Effect?
The UV range.
How does the Photoelectric effect work?
- Free electrons on the surface of the metal absorb energy from the light.
- If an electron absorbs enough energy, the bonds holding it to the metal break and it is emitted from the surface.
What are emitted electrons called?
Photoelectrons.
How can the Photoelectric effect be demonstrated with an Electroscope?
- The electroscope is initially negatively charged (gold leaf is repelled).
- The metal (often zinc) plate is exposed to UV light which (due to the photoelectric effect) causes free electrons to be ejected.
- The leaf drops as the charge is lost.
Why does the gold leaf bend up when negatively charged?
The leaf and the supporting bar are all negatively charged so repel each other.
Why does the Photoelectric effect not occur with a positively charged Electroscope?
The atoms do not have any free electrons to be emitted (due to positive charge).
Why is the metal plate often sanded?
To remove the oxide layer that forms on the top.
What is the threshold frequency?
The minimum frequency of which the radiation must be in order for electrons to be emitted.
Describe the properties of the emitted electrons in regards to Kinetic Energy.
The photoelectrons emitted have a variety of kinetic energies ranging from zero to a maximum value. The maximum KE value increases with frequency of radiation but is unaffected by intensity.
What is the relationship between emitted photoelectrons and radiation intensity.
Photoelectrons emitted per second is proportional to radiation intensity.
