X-ray diffraction from the crystal of a protein (hen egg lysozyme) produced this interference pattern. Analysis of the pattern yields information about the structure of the protein. (credit: “Del45”/Wikimedia Commons)
Summary
Radiation is absorbed and emitted by atomic energy-level transitions.
Quantum numbers can be used to estimate the energy, frequency, and wavelength of photons produced by atomic transitions.
Atomic fluorescence occurs when an electron in an atom is excited several steps above the ground state by the absorption of a high-energy ultraviolet (UV) photon.
X-ray photons are produced when a vacancy in an inner shell of an atom is filled by an electron from the outer shell of the atom.
The frequency of X-ray radiation is related to the atomic number
Z of an atom.
Conceptual questions
Atomic and molecular spectra are discrete. What does discrete mean, and how are discrete spectra related to the quantization of energy and electron orbits in atoms and molecules?
Atomic and molecular spectra are said to be “discrete,” because only certain spectral lines are observed. In contrast, spectra from a white light source (consisting of many photon frequencies) are continuous because a continuous “rainbow” of colors is observed.
NGC1763 is an emission nebula in the Large Magellanic Cloud just outside our Milky Way Galaxy. Ultraviolet light from hot stars ionize the hydrogen atoms in the nebula. As protons and electrons recombine, light in the visible range is emitted. Compare the energies of the photons involved in these two transitions.
UV light consists of relatively high frequency (short wavelength) photons. So the energy of the absorbed photon and the energy transition (
) in the atom is relatively large. In comparison, visible light consists of relatively lower-frequency photons. Therefore, the energy transition in the atom and the energy of the emitted photon is relatively small.
How do the allowed orbits for electrons in atoms differ from the allowed orbits for planets around the sun?
For macroscopic systems, the quantum numbers are very large, so the energy difference (
) between adjacent energy levels (orbits) is very small. The energy released in transitions between these closely space energy levels is much too small to be detected.
What is the minimum frequency of a photon required to ionize: (a) a
ion in its ground state? (b) A
ion in its first excited state?
For
, one electron “orbits” a nucleus with two protons and two neutrons (
). Ionization energy refers to the energy required to remove the electron from the atom. The energy needed to remove the electron in the ground state of
ion to infinity is negative the value of the ground state energy, written:
Thus, the energy to ionize the electron is
Similarly, the energy needed to remove an electron in the first excited state of
ion to infinity is negative the value of the first excited state energy, written:
Polarization is the process of transforming unpolarized light into polarized light.
types of polarization
1. linear polarization.
2. circular polarization.
3. elliptical polarization.
Eze
Describe what you would see when looking at a body whose temperature is increased from 1000 K to 1,000,000 K
In physics and mechanics, torque is the rotational
equivalent of linear force. It is also referred to as the
moment, moment of force, rotational force or turning
effect, depending on the field of study.
Teka
Torque refers to the rotational force. i.e Torque = Force × radius.
Arun
Torque is the rotational equivalent of force .
Specifically, it is a force exerted at a distance
from an object's axis of rotation. In the same way
that a force applied to an object will cause it to
move linearly, a torque applied to an object will
cause it to rotate around a pivot point.
Teka
Torque is the rotational equivalence of force . So,
a net torque will cause an object to rotate with an
angular acceleration. Because all rotational
motions have an axis of rotation, a torque must
be defined about a rotational axis. A torque is a
force applied to a point on an object about the
axis
Teka
When a missle is shot from one spaceship towards another, it leaves the first at 0.950c and approaches the other at 0.750c. what is the relative velocity of the two shipd
can someone help explain why v2/c2 is =1/2
Using The Lorentz Transformation For Time
Spacecraft S′ is on its way to Alpha Centauri when Spacecraft S passes it at relative speed c /2. The captain of S′ sends a radio signal that lasts 1.2 s according to that ship’s clock. Use the Lorentz transformati
