4.5 Quantum Physics Flashcards
What is atom spacing?
The distance between adjacent atoms in a crystal lattice, significant in electron diffraction experiments
What is de Brogiles equation?
An equation that relates the wavelength of a particle to its momentum: lamda = h/p
wavelength = plancks constant / momentum of particle
What is electron diffraction?
The bending and spreading of electrons when they pass through a narrow slit or around an obstacle , providing evidence of their wave like properties
What is an electronvolt (eV)?
A unit of energy equal to the amount of kinetic energy gained by an electron when accelerated through a potential difference of 1 volt
1eV = 1.6 x 10 ^-19
What is a photon?
A quantum ( or packet) of electromagnetic energy. Photon exhibit both particle like and wave like properties
What is the photon model?
A model of electromagnetic radiation that treats light as being made up of photons, explaining phenomena like the photoelectric effect that the wave model cannot
What is photon energy?
The quanitised enegry carried by a photon given by the equation E=hf
Energy = plancks constant x frequency
What is the photoelectric effect?
The emission of electrons from a metal surface when exposed to electromagnetic radiation of sufficient frequency. This effect provides evidence for the particle nature of light.
What is the photoelectric equation? (or Einstein’s equation)
An equation describing the photoelectric effect: hf = work function + KE(max)
energy of incident photon = work function + max kinetic energy of emitted photons
What is Plancks constant?
A fundamental constant on quantum physics that relates the energy of a photon to its frequency
h = 6.63 x 10 ^-34
What is the threshold frequency?
The minimum frequency of incident radiation required to eject electrons from the surface of a material on the photoelectric effect
What is wave-particle duality?
The concept in quantum physics that all particles exhibit both wave-like and particle properties.
This is evidence by the phenomena like the photoelectric effect (particle nature) and electron diffraction (wave nature)
What is the work function?
The minimum energy required to remove an electron from the surface of a metal.
It is material specific constant (although in later study is dependent on the contamination and roughness of the surface of the material as well)
How can we estimate Planck’s constant using an LED?
LEDs can be used to estimate Planck’s constant by finding the threshold voltage needed to emit light of known wavelength.
Using the equation eV=hc/lamda, and plotting voltage against 1/lamda for different LEDs, the gradient gives hc/e, allowing calculation h.
What is the gold leaf electroscope practical?
A negatively charged zinc plate on a gold leaf electroscope repels the gold leaf. When UV light is shone on the plate, electrons are emitted, reducing the charge and causing the gold leaf to fall.
What does the gold leaf electroscope practical prove?
It demonstrates the photoelectric effect — that light can cause electron emission only if its photons have enough energy (i.e. high enough frequency), supporting the particle model of light over the wave model.
