Chapter 4: Particles of Light Flashcards
What is the photoelectric effect?
The emission of photoelectrons from a metal surface when exposed to e-m radiation of a high enough frequency
What is a photon?
A quantum of light which is a small indivisible packet of energy
What is frequency proportional to for photons?
The energy of the photons
What is intensity proportional to for photons?
The number of photons arriving per second per unit area
What is the threshold frequency?
The minimum frequency of light (photons) required for photoelectrons to be emitted from a metal surface through the photoelectric effect
What is the work function?
The minimum energy required to remove an electron from a metal’s surface through the photoelectric effect
What is Einstein’s photoelectric equation?
E= hf= Φ + Ekmax
E= energy
h= Planck’s constant
f= frequency of the radiation (Hz)
Φ= work function of material (J)
Ekmax= max. kinetic energy of photoelectrons (J)
What is the stopping potential?
The minimum negative voltage applied to the anode to stop the photocurrent.
The maximum kinetic energy of the electrons equal the stopping voltage, when measured in electron volt.
How is stopping potential calculated?
eVstop= Ekmax
What is the equation for de Broglie wavelength?
λ= h/p
λ= de Broglie wavelength (m)
h= Planck’s constant
p= momentum (mv) (kgms-1)
What is electron diffraction and what is it evidence for?
The spreading of electrons as they pass through a gap similar to the magnitude of their de Broglie wavelength to produce a diffraction image.
It is evidence of the wave-like properties of particles
What happens during electron diffraction?
-Beam of electrons fired from electron gun (cathode ray gun) through thin graphite screen.
-Arranged in lattice and acts like a diffraction grating, electrons diffract and interfere to form a single pattern of diffraction rings.
How does de Broglie wavelength change as momentum increases?
As momentum of electrons increases, de Broglie wavelength decreases and so the electrons diffract less, causing smaller spaced rings.
What is wave-particle duality?
The idea that matter and radiation can be described best by sometimes using a wave model and sometimes using a particle model
What are some examples for wave-like properties and particle-like properties?
Photoelectric effect: particulate nature
Electron diffraction: wave nature
Excitation and de-excitation: particulate nature
Young’s double slit: wave nature
