Quanta Flashcards
What is meant by ‘quantum’? (Quanta)
The minimum amount of any physical property involved in an interaction.
What does Quantum Theory attempt to explain? (Quanta)
Phenomena and experimental observations which could not be explained by classical physics.
Who was Quantum Theory first proposed by? (Quanta)
Max Planck in 1900.
What is Quantum theory required to make sense of? (Quanta)
A number of experimental observations, such as spectra, which classical physics can’t explain.
What is a black body? (Quanta)
A surface that absorbs all wavelengths of electromagnetic radiation and is also the best emitter of e.m radiation at any wavelength.
What is the continuous spectrum of radiation a black body emits called? (Quanta)
Black body radiation
What is the ultraviolet catastrophe? (Quanta)
When the graph created by Lord Rayleigh and J.H. Jeans’ equations tended to infinity at shorter wavelengths.
How did Planck manage to produce a mathematical equation which could correctly predict black body graphs? (Quanta)
He made the assumption that the absorption and emission of radiation could only take place in discrete jumps termed quanta.
What equation is used to calculate energy in a quanta jump (Quanta)
E = nhf
When does the photoelectric effect occur? (Quanta)
When electromagnetic radiation is directed at a metal surface and ejects electrons from the metal.
Sketch a diagram of the photoelectric effect (Quanta)
Remember:
- Metal plate
- Photons travelling into plate from left
- Electrons coming out of plate at right
Which equation is used to calculate the energy of a photon? (Quanta)
E = hf
What is wave-particle duality? (Quanta)
The view that electromagnetic radiation acts both like a wave and like a particle simultaneously
What is one piece of evidence for waves behaving like particles? (Quanta)
The photoelectric effect: particles of light (photons) causing electrons to be ejected from a metal surface.
What is one piece of evidence for particles behaving like waves (Quanta)
Electron diffraction: An electron beam bombarding thin films of metal producing diffraction rings (concetric circles)
What is compton scattering? (Quanta)
An experiment performed by Arthur H Compton which he observed the scattering of x-rays from electrons in a carbon target
Sketch a diagram for Compton Scattering (Quanta)
Remember;
- Incident x-ray photon travelling into electron
- Recoil electron moving up outwards from electron
- Scattered x-ray photon with longer wavelength moving down outwards from electrom
What did Compton’s experiment give clear evidence of? (Quanta)
Particle-like behaviour by electromagnetic radiation.
What is the uncertainty principle in terms of the position and momentum of a quantum particle? (Quanta)
It is not possible to measure the position and momentum of a particle simultaneously
What is the uncertainty principle in terms of the energy and lifetime of a quantum particle? (Quanta)
It is not possible to know the lifetime of a quantum particle and its associated energy charge simultaneously.
Why is quantum physics needed to account for quantum tunnelling? (Quanta)
•Consider an electron near an energy barrier.
Classical physics - electron will bounce off of barrier unless it has enough energy to ‘leap’ over it
Quantum physics - even if the electron has energy lower than the barrier, there is finite probability that it can ‘tunnel’ through to the other side
What is meant by ‘cosmic rays’? (Quanta)
Energetic particles from outer space which enter the earth’s atmosphere.
What two types of particle make up the majority of all cosmic rays reaching the Earth’s atmosphere? (Quanta)
Protons - 89%
Alpha particles- 9%
What happens when the cosmic rays strike the top of Earth’s atmosphere? (Quanta)
A cosmic air shower is produced
- This is a shower of secondary particles including electrons, photons, neutrinos and muons.
Why will charged particles enter the Earth’s magnetic field will follow a helical path? (Quanta)
If particles enter the magnetic field at an angle, the two components of a particle’s velocity cause it to foow a helical path
Component perpendicular to the magnetic field creates the circular motion, parallel component creates pitch in helix
What is meant by the ‘solar wind’? (Quanta)
A stream of charged particles which escale from the upper atmosphere of the sun.
It flows outwards as a plasma at high speed.
How does the Earth retain it’s atmosphere despite being exposed to the solar wind? (Quanta)
The Earth’s magnetic field helps to retain it’s atmosphere since it deflects the solar wind around the planet.
How are the northern and southern lights produced? (Quanta)
Cosmic particled trapped in Earth’s magnetic field enter atmosphere neart north and south poles.
Nitrogen, oxygen molecules become excited and emit light when they return to their ground state.
What is meant by ‘Simple Harmonic Motion’ (SHM)? (Quanta)
The repeated motion of an object under the influence of an unbalanced force (restoring force).
Which direction does the restoring force act towards? (Quanta)
The equilibrium position, is proportional to the object’s displacement.
What is an example of SHM? (Quanta)
A mass on a string.
What is meant by ‘damping’ in SHM? (Quanta)
When an oscillating system loses energy to frictional forces.
The amplitude of the motion decreases to 0 over time.
What is the formula for displacement when y=0 and t=0 (Quanta)
y = A x (sin) x w x t
What is the formula for displacement when y=A and t=0 (Quanta)
Y = A cos wt
Deprive an expression for velocity (v) (Quanta)
Start with v=dy/dt
Differentiate y = Asinwt with respect to t:
V = d/dt x (Asinwt)
V= Awcoswt
since sin^2wt + cos^2wt = 1 then
v = _+_Aw(sqrt)1-sin^2wt
Simplified: v= _+_Aw(sqrt)1- y^2/A^2
v= _+_w(sqrt)A^2 - y^2
What is the equation to find maximum velocity when y = 0? (Quanta)
Vmax = Aw
Deriving an expression for Acceleration (Quanta)
a = dv/dt = d^2y/dt^2
Differentiating with respect to t:
a = d/dt x (Awcoswt)
a = -Aw^2 x sinwt
Since y= Asinwt:
a = -w^2 x y
What is he equation to find maximum acceleration of an object undergoing SHM (Quanta)
amax = w^2 A
What is the equation to find Kinetic Energy in SHM (Quanta)
Ek = 1/2 mv^2 (A^2 - y^2)
What is the equation to find maximum kinetic energy? (Quanta)
Ek,max = 1/2 mw^2A^2
What is the equation to find potential energy? (Quanta)
Ep = 1/2mw^2y^2
