FSc ICS Notes Physics XII Short Questions & Definitions Chapter 20 Atomic Spectra 2nd Year Physics Notes Online Taleem Ilmi Hub
If you want to view Exercise Question & Numerical Problems. Please refer to this page Physics Part 2
Spectroscopy: Branch of physics deals with the production and analysis of spectra.Absorption spectrum: A continuous spectrum interrupted by dark lines or bands which appear at points where absorbed frequencies would normally occur.
Emission spectrum: The spectrum observed when electromagnetic radiation coming directly from an incandescent source is examined with a spectroscope.
Molecular spectrum: The absorbed or emission spectrum that is characteristic of a molecule.
Continuous spectra: The spectra consisting of a wide range of unseparated wavelengths.
Line spectra (or Discrete spectra): Spectra consisting of monochromatic slit images having wavelengths characteristic of the atoms present.
Band spectra: The spectra that appear as a number of fluted bands of colour of emitted or absorbed radiation.
Solar spectrum: The band of colours produced when sunlight is dispersed by a prism.
Pure spectrum: The spectrum in which each colour of the light will form a separate sharp image of the narrow slit.
Elementary colours: The six regions of colour in the solar spectrum, observed by the dispersion of sunlight; red, orange, yellow, green, blue, and violet.
Black body radiation: The thermal radiation from a black body at a given temperature, having a spectral distribution of energy with some specific characteristics.
Spectrum:
- The set of colours obtained on the screen by dispersion.
- Array of colours arranged according to their wavelength.
Spectrometer: Optical instrument used for the study of spectra. It consists of collimator, turntable and telescope.
Collimator: The part of the spectrometer consisting of slit and a convex lens, which is called collimating lens.
Turn-table: The part of the spectrometer between collimator and telescope. This turntable is provided with three leveling screws. It is used for supporting the prism or the diffraction grating.
Telescope: A device for collecting and producing an image of distant objects.
Diffraction grating (or Grating): An optical surface, either transmitting or reflecting with several thousand equally spaced and parallel lines ruled on it.
Line spectrum: A spectrum consisting of monochromatic slit images having wavelengths characteristic of the atoms present.
Rydberg’s constant: A constant relating to those atomic spectra that are similar to the hydrogen atom spectrum. For hydrogen, it is 1.09677 x 10(-7) m. The general Rydberg formula is;
1 / λ = R ( 1 / p2 - 1 / n2 )
Balmer series: The visible spectrum of hydrogen. It consists of sharp distinct lines corresponding to second lowest energy level.
Lyman series: A series of lines that occurs in the ultra-violet region of the spectrum of hydrogen, corresponding to lowest energy level.
Ultraviolet region: The region just beyond the violet end of the visible spectrum. Its range is between about 1 nm and 400 nm.
Infrared region: The region past the red end of the visible spectrum. The range of wavelengths is approximately 0.7 μm to 1 mm.
Paschen series: A series of lines that occurs in the infra-red regio0n of the spectrum of hydrogen.
Brackett series: A series of lines that occurs in the far Ingra-red region of hydrogen spectrum. They correspond to the atomic electrons falling into the fourth energy level and emitting energy as radiation.
Pfund series: A series of lines that occurs in the far infra-red region of hydrogen spectrum. They correspond to the atomic electrons falling into the fifth energy level and emitting energy as radiation.
Planck’s quantum theory:
- According to it the radiant energy of a system or the exchange of radiant energy between different systems occurs not in a continuous fashion permitting all possible values, as demanded by the wave theory but in a discrete quantified form, as integral multiples of an elementary quantum of energy.
- A unified theory which assumes that the transfer of energy between light radiations and matter occurs in discrete units, the magnitude of which depends on the frequency of the radiation.
Classical theory:
- The long established part of physics excluding relativity and quantum theories.
- The part of physics that was developed before, and therefore does not include, either quantum theory or the theory of relativity.
Postulate: A statement which is taken for granted as a fact ; to assume without proof.
Hypothesis: A theory, which may or may not prove to be true.
Law: A scientific statement of the action and relation of things in nature, observed to be always the same under given conditions with the same result performed anywhere in the world.
Principal quantum number: An integral multiple, n, for allowed stationary orbits in Bohr’s atom model. It takes only integral values 1, 2, 3, ……, n.
Spectroscopy: Branch of physics deals with the production and analysis of spectra.
Ionization: The process of producing ions.
Ionization energy (or Ionization potential): The energy required to remove an electron from an atom or molecule to form a positive ion.
Binding energy:
- The energy needed to break up a nucleus into its constituent particles.
- The energy equivalent to the difference between the mass of the nucleus and the sum of the masses of its constituent nucleons.
Ground state ( or Normal state): The state of a system with the lowest energy. An isolated body will remain indefinitely in it.
Excited state: The state of a system, such as an atom or molecule, when it has a higher energy than its ground state.
Excitation potential: The potential through which an electron should be accelerated so that, on collision it can lift the electron in the atom from its ground state to some higher state.
Transition: A sudden change in the energy state of an atom or nucleus between two of its energy levels.
Shell: The electrons with the same principal quantum number ‘n’ are said to form a shell.
Sub-shell: The electrons in each shell are arranged in subshells, specified by the value l ( l = 0, 1, 2, …., n-1). In Bohr’s theory n and l determine the size and shape of the orbit.
X-rays: Electromagnetic radiation of extremely short
wavelength, having great penetrating power.
Characteristic X-rays: When X-rays are made to fall on the target material, and electrons in the inner most shells will be knocked out. The photons emitted from inner shell transitions are called characteristic X-rays, because their energies depend upon the type of target material.
Cadmium ( 48Cd112 ): A soft bluish metal, used in low melting point alloys to make solders in some batteries.
Bremsstrahlung (or Breaking radiation): X-rays emitted when fast electrons are slowed down violently, as when electrons strike the target in an X-ray tube. The word translates as ‘breaking radiation’. Bremsstrahlung is caused when an electron passes through the electric field of a nucleus and constitutes the continuous X-ray spectrum.
CAT: Stands for ‘Computerized axial tomography’.
Tomography: A method of radiography that focuses an organ or plane, thus eliminating the confusing shadow of the ordinary radiogram, which makes diagnosis so difficult.
CAT scanner: A computerized system for scanning shadow photographs of the internal structure of the body with direct focus on an organ to eliminate confusing shadow.
Susceptible: Capable of getting a disease, deficient in defences against a disease.
Radiography: The production of shadow photographs of the internal structure of bodies opaque to visible light by the radiation from X-rays, or by gamma-rays from radioactive substances.
Radiograph: The shadow photographs obtained in the process of radiography.
Scanning: The process of exploring an area or volume in a methodical manner, in order to produce a variable electrical output whose instantaneous value depends on the information contained in the small area examined at each instant.
Topography: The determination and description of the arrangement of parts in a region of the body, or of the external anatomy of an animal.
Tumour: An abnormal swelling or enlargement in any part of the body of an animal or plant; an excrescence. Usually a permanent swelling without inflammation, caused by excessive continued growth of cells in a tissue. .
Proteins: Any of a large group of organic compounds found in all living organisms. Proteins comprise carbon, hydrogen, oxygen and nitrogen also sulphur.
Genetic: Pertaining to, or involving origin; arising from a common origin. Sequences of nucleotides in chromosomal DNA or RNA, different groups of three consecutive nucleotides corresponding to different amino acids.
DNA (Deoxyribonucleic acid) : A nucleic acid containing a sugar component; a self-replicating material present in nearly all living organisms, esp. in chromosomes, as the carrier of genetic information and the determiner of protein synthesis, usually occurring as a molecular double helix in which a phosphate group alternates with a sugar molecule linked to a base.
Chromosome: A threadlike structure of nucleic acids and protein which carries a set of linked genes and in characteristic numbers, usually paired, in the cell nuclei of higher organisms.
RNA: Any of the nucleic acids which yield sugar on hydrolysis, occurring chiefly in the cells, where they direct the synthesis of proteins, and as the genetic material in some viruses.
Cancer cells (or Cancer): A malignant tumour or growth of body tissue that tends to spread and may recur if removed; disease in which such a growth occurs.
Malignant: .A disease liable to become progressively more severe; extremely virulent; very infectious. Now chiefly of a cancer or tumour: tending to spread to other parts of the body, or to recur after removal.
Anatomy: The science of the structure of the bodies of humans, animals, and plants; a treatise in this field.
Anatomical: Of or pertaining to the study or practice of anatomy; structural.
Laser: (Light Amplification by Stimulated Emission of Radiation); a device which is able to produce a beam of radiation with unusual properties, generally the beam is coherent, monochromatic, parallel with high intensity.
Maser: (Microwave Amplification by Stimulated Emission of Radiation); a device for producing an intense source of coherent microwave radiation. Masers, like lasers, operate by population inversion and stimulated emission.
Acronym: A word formed from the initial letters or parts of other words; loosely an abbreviation composed of initial letters.
Stimulate: To rouse and produce greater activity in.
Monochromatic: Light consisting of only one colour.
Coherent: Having same phase, i.e. peaks and troughs always come together.
Phase coherence: Producing of two waves at the same instant, having same wavelength and time period.
Intensity: The energy transmitted per second through a unit area by the light waves.
Stimulated ( or Induced) absorption: Absorption of incident photon by an atom in the
ground state, thereby leaving the atom in the excited state.
Stimulated (or Induced) emission: The incident photon of energy induces the atom in excited state, to decay by emitting a photon that travels in the direction of the incident photon, to get unidirectional coherent beam.
Metastable state:
- It is an excited state in which an electron spontaneously falls to lower state only after relatively longer time.
- A condition of a system or body in which it appears to be a stable equilibrium but, if disturbed, can settle into a lower energy state.
Population inversion: A net emission of photons with more number of atoms in the excited state than in the ground state.
Organelle: Any of various specialized structures in the material of an individual cell or unicellular organism, analogous to the organs of multicellular organisms.
Retina: The inner, sensitive coating of the eye containing the ends of the nerves of sight; that part of the eye which receives images of object.
Iris: The circular coloured membrane of the eye.
Pupil: The opening in the iris of the eye, through which rays of light pass to the retina.
Lymph: A colourless fluid in plants; A colourless alkaline fluid, resembling blood but lacking red cells, which bathes various tissues and organs of the body and drains into the bloodstream through a network of vessels.
Optical fibre: An optical fibre consists of a single flexible rod of high refractive index, less than 1mm in diameter, having polished surfaces coated with transparent material of lower refractive index.
Refractive index ( or Absolute index of refraction): The ratio of velocity of light in vacuum to its velocity in a given substance. n = c1 / c2
Holography: A method of recording, usually photographically, a three-dimensional image of an object.
Ophthalmology: The branch of medicine that deals with the structure, functions, and diseases of the eye.
Post a Comment