Em Radiation And Quantum Phenomena Flashcards
What is the photoelectric effect
If you direct EM of a high enough frequency onto a metal it ill emit photo electrons
Why does the photoelectric effect happen
Photons of high enough energy hit free electrons, if the energy of the photon is high enough then it will give the electron enough energy to break free
What does/ does not affect ek max
Frequency effects it but intensity doesn’t
How do you increase the number of photo electrons per second
Increase the intensity
How does an electron move down an energy level
It emits photons
Why are photon wavelength and energies discrete
The energy needed for an electron to move down shells is discrete and the energy levels in an atom are discrete, therefore the energy a photon has is discrete and so must its wavelength
What’s excitation
When an electron absorbs the exact energy needed to move from one energy level to the next, from a photon, and it moves up to a higher energy state
What’s ionisation energy
The energy needed to completely remove and electron from the fround state of an atom
What is stopping potential
The potential difference needed to stop the fastest electron
How does stopping potential work
The electrons lose their energy as they are made to do work against a potential difference
What is an electron volt
The kinetic energy carried by an electron after it has been accelerated through a potential difference of 1v
How many joules is in 1eV
1.6x10-19
Maximum kinetic energy
The kinetic energy is hf, the minimum energy lost by the electron is the work function , therefore they will have a maximum kinetic energy and Ek is hf-work function
Why do electrons emitted have different energies
The energy given by the photon is constant at hf, the deeper electrons the more energy it takes to escape, therefore there are different energy levels, and different kinetic energies
What is threshold frequency
The minimum frequency needed for a photon to have enough energy to emit an electron
What is the work function
The minimum energy an electron needs to leave the surface of a metal
What is characteristics of wave theory
- for a particular frequency then E would be dp to the intensity
- energy would spread out evenly on the wavefront
- each electron would gain a fraction of the energy from a wave
- gradually an electron would escape
Why does wave theory not work for photoelectric effect
The energy is dependent on intensity, but in frequency
Electrons won’t be eventually emitted
Wave theory can’t explain threshold frequency
What is photon model of light
Em waves exist in discrete packets called photons
How does photon theory explain photoelectric effect
E=hf which explain why energy is dependent on freuqency and it explains threshold freq
The particles have one to one interaction and there is no time delay
How do fluorescent tubes work?
The contain mercury vapour and they apply a high voltage which accelerates free electrons, these ionise Mercury atoms creating more free electrons
Free electrons collide with other Mercury atoms and excite them to higher energy levels,
The de-excite emitting photons in the UV range
A phosphorus coating absorbs the photons and electrons are excited to higher orbits
Electrons cascade down the energy levels emitting lower energy photons in the form of visible light
What’s line emission spectra and where does it occur
A spectrum which contains a few bright lines against a black background, these have specific wavelengths, this occurs when the light from de-exciting electrons is split using a prism or diffraction grating
Why do line emission spectrums have specific lines
Each line correlates to a specific wavelength and as photons have discrete energies they have discrete wavelengths
What’s a continuous spectra
Colours all merge into one an another and there are no gaps
