Wave Particle Duality Flashcards
Explain Bremsstrahlung’s curve
- The smooth curve continuous section of the graph is created by the full range of Bremsstrahlung X-rays
- emitted by the colliding electrons with the target anode
- The peaks are due to X-rays produced when colliding electrons knock electrons out from inner shell of the target anode
- whereupon a higher energy electron drops back to fill the vacant position emitting an X-ray photon - this is a characteristic of the target anode used in the X-ray machine
Name and describe the process by which the photoelectrons are released from the plate by electromagnetic radiation
- The process is called the photoelectric effect.
- When a photon with enough energy (E=hf) hits a surface electron on the plate, it can knock the electron off.
- But only if the frequency of light = the threshold frequency.
- The interaction in one photon to one electron so if the light is more intense, more electrons will be emitted
Define photon
A packet of EM radiation with a specific amount of energy depending on its frequency
Define threshold frequency
The minimum frequency of EM radiation at which electrons will be emitted when hit by that EM radiation
Describe what occurs within the atom when an atom is induced to emit its line emission spectra
- Electrons that have been promoted to higher energy levels
- Cascade back to the ground state emitting photons equivalent to each line emission
With reference to the discovery of helium, explain the origin and significance of lines in the solar spectrum
- Sun emits a continuous spectrum with absorption lines
- Absorption lines are specific to orbital energy differences of atoms/molecules
- Atoms absorb energy and re-emit in all directions creating dark lines(scattered)
- Absorption lines could all be accounted for by known elements except for a set of ‘unknown lines’ which must be from a new unknown element
Young’s Double Slit
- Diffraction spreads the light sideways
- Interference: dark where destructive, light where constructive
- Only wave theory explain interference pattern formed
Explain why light can be described as an EM wave but not as a mechanical wave
- A mechanical wave requires particles of matter in a medium to be oscillated to enable the energy to transfer from one point in space to another
- Light is propagated as an electric field and a magnetic field that are at right angles to each other
- This enables light to travel through a vacuum where no particles exist to be oscillated
- So light cannot be classified as a mechanical wave
Black body radiation
- A black body is an object that can absorb and emit all wavelength of light without any reflection
- Classical theory predicted that all wavelengths would contain the same amount of energy and emission was due to electric oscillators vibrating at the fundamental and higher harmonics
- As the harmonic number increases more and more energy would be emitted up to an infinite number of harmonics which would result in an infinite energy at short wavelengths
- Quantum theory however shows that the higher harmonics would contain more energy than the low harmonics because Planck showed that E=hf and hence less photons would be emitted to achieve the same energy output
Why does metal change colour when heated?
- At the higher temp the metal is emitting photons with a higher energy.
- As E=hf, this means more waves with a higher frequency and shorter wavelength
- Hence there will be a larger number of waves with higher wavelength and hence higher intensity towards the blue end of the spectrum
- This mixture of all colours, including blue looks white to the eye
- At the lower, less energetic, temperatures there are far less waves in the blue region and hence the metal appears grey or red if it is warmer than that
Huygens’ Principle
Each point on a wavefront can be considered as a source of secondary wavelets
Polarisation
Polarisation occurs when a transverse wave is only allowed to oscillate in one direction
Michelson-Morely Experiment
- Testing if there was an ‘aether’
- Beam of light was shone into a mirror that was only partially coated in silver
- Part of the beam would be reflected one way, and the rest would go to the other
- Then reflected back to where they were split apart, recombined
No change in light speed was found
Photoelectric Effect
- Light can cause electrons to be ejected from some metal surfaces
- Stopping voltage depends only on the frequency of the incoming light and is independent of the intensity
Einstein’s theory
An electron is ejected when the energy of the incident photon exceeds the energy binding the electron in the metal
Ionisation
If enough energy is absorbed, and outer orbital electron may be completely ejected
Atom becomes an ion
