Atomic physics, electromagnetic waves, X-ray Flashcards
Give the energy and momentum of a photon with frequency f
The energy of a photon with frequency f is hf, and its momentum is hf/c=lambda/h, where h and c are Planck’s constant and the speed of light in vacuum, respectively, and lambda is the wavelength of the photon.
Align in ascending order the following components of the electromagnetic spectrum according to their energy: microwaves, gamma, ultraviolet, visible light, X-ray, infrared, radiowaves!
radiowaves < microwaves < infrared < visible light < ultraviolet < X-ray, gamma
What is the definition of visible light?
The range of electromagnetic radiation observable by the human eye (approximately 400-750 nm).
Define the limiting frequency (fmax) of braking radiation at an accelerating voltage of U.
fmax=eU/h where h is Planck’s constant and e is the charge of an electron
List the three most important mechanisms responsible for the absorption of gamma and X-rays!
- photoelectric effect
- Compton-effect
- pair-production
What is the major difference between the photoeffect and the Compton effect?
All of the energy of the X-ray (or gamma) photon is used to ionize the atom and set the electron in motion in photoelectric effect. On the contrary, only part of the photon energy is used for these processes in Compton effect, and the photon having lower energy is scattered.
What is the minimal energy of a gamma-photon needed for pair-production (not numerically)?
The energy equivalent to the rest mass of an electron and a positron according to the Einstein mass-energy equivalence equation: E=(me+mp)c^2, where me and mp are the rest masses of an electron and a positron, respectively, c is the speed of light in vacuum and E is the minimal energy of a gamma-photon inducing pair production.
Why is a heavy nucleus necessary for pair- production?
The presence of a heavy nucleus is required by the law of conservation of momentum.
What is annihilation?
The process in which an electron and a positron (or in general a particle-antiparticle pair) collide with each other and the total mass-energy of this particle system is converted to the energy of two gamma photons, is called annihilation.
Define interference.
Interference is the superposition of waves that results in the generation of a new wave pattern.
What is constructive and destructive interference?
Interference is constructive when the amplitude of the resultant wave is greater than the amplitudes of the individual waves, and it is destructive when the amplitude of the resultant wave is less than that of the individual waves.
What is the requirement for maximally constructive and maximally destructive interference if two propagating waves with identical wavelength interfere with each other?
Maximally constructive interference takes place, if the path difference (Delta s) between the waves is an integer multiple of the wavelength (lambda): Delta s = l lambda , where
l=0,1,2,3…. This happens when the crest of one of the waves is superimposed on the crest of the other one. Maximally destructive interference is generated, if Delta s = (l+1/2)lambda, i.e. when the crest of one of the waves is superimposed on the trough of the other one.
Give the condition for constructive interference for an electromagnetic wave with wavelength lambda diffracted on a crystal with a grating constant of c! (angle of incidence is 90)
c cos alpha=l lambda , where l=0,1,2,3,…n, alpha=angle of diffraction
What is the definition of transverse and longitudinal waves?
In a transverse wave the displacement of oscillating particles is perpendicular to the direction of propagation of the wave. In a longitudinal wave the displacement is parallel to the direction of propagation
