Quantum- nanowereld Flashcards
1 - Q1
The answer is no. The name of the black body came from the fact that it is a theoretically ideal absorber of electromagnetic radiation.
However, this make it a perfect emitter. At the room temperature, the black body looks black, but if we heated it enough it would start to emit light, according to the black-body radiation spectrum.
1 - Q3
1 - Q5
1 - Q6
1 - Q8
In classical thermodynamic theory, the blackbody emits radiation for all frequencies, and the emitted energy increases as the frequency increase without limits. Experimentally, it is observed that the energy emitted by a blackbody is finite, which causes the matter to radiate all of its energy until it is near absolute zero, this contradiction between the theoretical expectation and the experimental observation called the ultraviolet catastropheultraviolet catastrophe.
1 - Q4
2 - Q1
No; both quantum theory and classical theory predict that the current will be proportional to the intensity of light, but for different reasons. In classical theory, a higher intensity implies that the velocity of the electrons will be higher because the electric field would be stronger. In quantum theory, a higher intensity means that there are more photons hitting the surface, meaning that more electrons are emitted
2 - Q3
Because each electron requires a different amount of energy to be emitted. This means that they will have differing levels of kinetic energy and thus differing velocities
2 - Q4
In classical theory, the energy given to the electron depends on the intensity of light. Because of this, the frequency of the light should not influence the energy and yet it does. In reality, the energy given to the electron depends on the frequency (E =hf), explaining the presence of a cutoff frequency. The intensity only determines how many electrons will be emitted, but not their energy
2 - Q6
The photoelectric effect suggests that we should think of light as a collection of many particles, not as a wave. Young’s interference experiment, however, is proof that light behaves as if it was a wave, so there is a seeming contradiction here.
The solution to this contradiction is that photons are particles with wave-like properties. The interference pattern is present in the experiment because each photon has a certain chance to be at any spot in the pattern. The bright spots have the highest chance, and the dark spots have the lowest. Thus, the resulting pattern is a statistical average of the individual behaviour of the particles.
2 - Q10
We would expect the Compton effect to be the same across any material used as the scatterer because if it were dependent it would suggest either some sort of process of absorption and re-emission or some sort of interaction with the nucleus.
We know, however, that Compton scattering occurs between the incident photon and the electron and that there is no absorption of the photon in this process, which rules out both of these reasons.
2 - Q12
The Compton effect assumes that the electron is unbound. Effectivelly, this means that the binding energy of the electron is much smaller than the energy of the incident photon that would experience Compton scattering. Binding energies of free electrons in solids are of the order of eVeV, and this is greatly exceeded by the energies of x-rays that are of the order of 0.1−100 keV0.1−100 keV. However, photons corresponding to visible light have energies of the order of eVeV which is comparable to the binding energies of electrons and the analysis for Compton scattering doesn’t hold in this case.
2 - Q17
For example, it can be determined in the photoelectric effect by measuring the energy of emitted electrons when the metal plate is shined on by a laser of known frequency. The constant of proportionality between the energy and the frequency of the photon will be Planck’s constant. The other way to measure it would be by using black body radiation. In the experiment, we can measure the power output of a lightbulb and its dependence on its temperature. From that data and Planck’s law of black body radiation, Planck’s constant can be determined.
Another way is to measure the stopping potential for different frequencies.
3 - Q1
The wavelength of an object λ and magnitude of its momentum p are related via the de Broglie relation
λ=h/p
where h is the Planck constant. Since h is extremely small, for macroscopic objects that we see in our everyday lives, λ would also be extremely small and incomparable to the dimensions of these objects and distances over which they travel, and this is why we will not observe their wavelike properties.
3 - Q3
