Quantum theory Flashcards
How does Young’s Double Slit experiment provide evidence for the wave model of light
Young observed interference patterns that were similar to those seen in water waves
Describe light waves
Light is an electromagnetic wave produced by an oscillating electric charge that produces mutually perpendicular oscillating electric fields and magnetic fields
Explain the concept of black-body radiation
The radiation emitted by a black body from the conversion of thermal energy; a black body is a perfect absorber or emitter of radiation
Identify that black body radiation provides evidence that electromagnetic radiation is quantised into discrete values
Wave-based theories predicted that energies from black bodies would increase to infinity which contradicted observations. Max Planck came up with an equation where light was quantised and this matched observations
Describe concept of a proton
A photon is a quantum (smallest discrete amount of electromagnetic radiation. It is a type of elementary particle (a gauge boson) that is the force carrier for the electromagnetic force
Describe the photoelectric effect in terms of a photon
The photoelectric effect is the emission of photoelectron from a clean metal surface due to an interaction with a photon. the photon model explains the existence of a threshold frequency for each metal and why brighter light results in a higher photoelectric current
Define the term threshold frequency
The minimum frequency of a photon that can eject an electron from a surface
Define planck’s constant
Planck’s constat is a fundamental constat used in quantum mechanics. Symbol, h and SI unit- Js
Define “work function”
The minimum energy required to remove an electron from a solid. Symbol, W and SI unit J
Recall the characteristics of a photon
Photons exhibit the characteristics of both waves and particles
Describe Rutherford’s model of the atom
The atom is a mostly empty space with a tiny very dense positively charged nucleus surrounded by even tinier, much lighter, negatively charged electrons
What are the limitations of the rutherford model?
Rutherfords model has electrons in circular orbits. Electrons changing velocity should emit energy meaning the electrons should spiral inwards towards the nucleus. rutherfords model also allowed electrons to have any energy, and thus light produced by atoms would have a continuous spectrum opposed to the emission spectra observed
Describe the Bohr model of the atom
In the Bohr model, electrons move in circular orbits using the electrostatic force of attraction with the nucleus to maintain the orbit. A number of allowable orbits of different radii exist for each atom and are labelled n = 1, 2, 3, etc. Electrons can occupy these orbitals. An electron does not radiate energy while in an orbital but can absorb energy to jump to higher orbits and emit energy to jump to lower orbits
How did Bohr model address limitations of Rutherford model
Electrons do not emit energy when a stable orbital and absorption and emission spectra result from electrons jumping between energy levels
How does Bohr model of hydrogen explain its emission spectra
the Bohr model integrates light quanta and electron energy levels. the emission spectrum for hydrogen shows that hydrogen electrons can only occupy specific energy levels and emit light of specific quanta
Describe wave-particle duality of light and identify evidence
Light exhibist wave properties of diffraction, interference and polarisation. light also has particle properties that explains the photoelectric effect and Compton scattering which showed light has momentum. when light interacts with light, it displays wave properties and when light interacts with matter, it has particle properties
What is Planck’s equation for the energy of a quantum of light
E= hf where h is plancks constant and f is the frequency of light in Hz
What is the formula for the maximum kinetic energy of a photoelectron
Ekmax= hf- W where W is the work function of the metal, W can be measured in J or EV so convert planck’s constant
What is the formula for Work Function
W= hf (subscript o), where f subscript o is the threshold frequency to eject an electron for a particular metal
What is DeBrogiles equation
Landa= h/mv where p=mv
All particles in matter can display wave properties and can be calculated with this equation
Recall the formula describing the condition for an electron to form a standing wave as an orbit of a nucleus
n*wavelength= 2pi(r)
n is an integer for the principal quantum number or energy level and r is the radius of the orbital in meters
