19. Quantum Physics Flashcards
What is photoelectric effect?
Photoelectric effect is the ejection of an electron from a metal surface when the surface is irradiated with electromagnetic radiation of high enough frequency.
Why must the experimental set up to observe the photoelectric effect be carried out in a vacuum?
To ensure that emitted photoelectrons are not obstructed by air molecules
What is stopping potential Vs?
KE max= eVs
The stopping potential Vs is the minimum potential difference to reduce the photoelectric current to zero. All kinetic energy of the most energetic electron will be converted into electrical potential energy eVs.
What is threshold frequency?
Threshold frequency is the lowest frequency of radiation that ejects electrons from a particular metal surface.
Describe how photoelectric effect provides evidence for the particulate nature of electromagnetic radiation. (3 observations)
- emission of photoelectrons starts with no observable time lag, even for very low intensity of incident light, assuming the frequency f exceeds threshold frequency.
- For a given metal, no electron emitted if the frequency of radiation is below threshold frequency f๐พ, even with high intensity of radiation. Above the threshold frequency, the maximum kinetic energy of emitted electrons increase linearly with frequency of radiation, even with low intensity.
- Increasing the intensity of the radiation has no effect on the maximum energy of the electrons.
These observations provide evidence that the light transfers energy to electrons in discrete amounts instead of continuous energy transfer like waves and the interactions between photons and electrons are one to one.
what is the evidence for the wave nature of electromagnetic radiation?
Interference and diffraction provide evidence that electromagnetic radiation is a wave.
When a monochromatic light is passed through a single slit followed by a double slit, a fringe pattern is produced on the screen.
These observations suggest that in its propagation through space, an electromagnetic wave behaves like a wave.
What is a photon?
A photon is a quantum of electromagnetic energy which is dependent only on the frequency of radiation.
What is the formula of energy of a photon? ( in terms of frequency)
Ephoton = hf
h is planck constant
f is frequency
What is the formula of energy of a photon? ( in terms of wavelength)
Ephoton = h c/๐
h is planck constant
c is speed of light in a vacuum (m/s)
๐ is wavelength (m)
what is work function energy ๐ ?
work function energy ๐ is the minimum energy required to eject an electron from its metal surface.
What is einsteins photoelectric equation?
Ephoton = ๐ + KE max
When does Eloss occur for an electron?
Eloss occurs when the electrons are deep in the metal and collide with the lattice ions and other free electrons as they make their way to the surface.
what is 1 electron volt eV ?
1eV = 1.60โ๏ธ10โปยนโนJ
it is the work done on an electron to move it through the potential difference of 1V
What is De Broglieโs equation?
๐ = h/p = h/mv
h is planck constant
p=mv, p is momentum
What is emission line spectra?
What is emission line spectra consist of quite separate bright lines of definite wavelength on a dark background and are given by luminous gases and vapours at low pressure.
What is absorption line spectrum?
Absorption line spectrum is a continuous spectrum crossed by dark lines due to some missing frequencies and is produced when white light passes through a cooler gas or vapour.
What is Bremsstrahlung?
Bremsstrahlung ( braking radiation ) describes the radiation which is emitted when fast-moving electrons are rapidly slowed down as they pass through the electric field around an atomic nucleus.
What are the characteristics X-rays?
Characteristic X-rays are emitted when an electron in an upper state (L- M-shells) of an atom drops down to fill the vacated lower state (K-shell) that has its electron dislodged by the bombarding electrons. The pattern of the characteristic X-rays is unique to each element.
What is the Heinsberg uncertainty principle?
Heinsberg uncertainty principle states that if a measurement of the position of a particle is made with uncertainty ฮx and a simultaneous measurement of its linear momentum is made with uncertainty ฮpx, the product of the two uncertainties is restricted to ฮpxฮx โฅ h
or ฮEฮt โฅ h
