12th Class Physics Atomic Physics Question Bank

done Case Based (MCQs) - Atoms Total Questions - 10

• question_answer1)

  Directions Q. 1 to 5: Read the following text and answer the following questions on the basis of the same:

  Atomic Absorption Spectrometer:

  The atomic absorption (AA) spectrometer is used to analyze metals at very low concentrations, typically in the parts per million (ppm) or parts per billion (ppb) ranges. A liquid sample containing dissolved material whose concentration is to be measured is aspirated into a thin, wide AA flame, or is introduced into a small carbon furnace which is heated to a high temperature.

  Basic Principle of AAS is the measurement of absorption of radiation by free atoms. The total amount of absorption depends on the number of free atoms present and the degree to which the free atoms absorb the radiation. At the high temperature of the AA flame, the sample is broken down into atoms using an atomizer and it is the concentration of these atoms that is measured.

  Sample in the form of solution is used. It is broken up into a fine mist with the help of an atomizer.

  When the mist reaches the flame, the intense heat breaks up the sample into its individual atoms.

  When a photon coming out from the hot source hits an atom and the energy of the photon is equal to the gap between two electron energy levels of the atom, then the electron in the lower energy level absorb the photon and jumps up to the higher energy level. If the photon energy does not correspond to the difference between two energy levels, then the photon will not be absorbed (it may be scattered away).

  Hence in the spectrum, the wavelength corresponding to the absorbed photons is observed as black lines as shown in the following spectrum of Hydrogen. The dark lines correspond to the frequencies of light those have been absorbed by the sample element.

  Using this process, a source of photons (generally a white light) of various energies is used to obtain the absorption spectra of different materials and to identify them.

  What is the basic principle of Atomic Absorption Spectrophotometer?
  A)
  Emission of photons when excited electron of an atom comes back to lower energy level. done clear
  B)
  Absorption of photons when electrons at lower energy level jumps to a higher energy level. done clear
  C)
  Emission of electrons from an atom at a very high temperature. done clear
  D)
  Emission of electron when energetic photons bombard an atom. done clear
  View Solution play_arrow

• question_answer2)
  What happens when a photon hits an atom and the energy of the photon is not equal to the gap between two electron energy levels of the atom?
  A)
  The photon is absorbed and the electron moves to an intermediate energy level. done clear
  B)
  The photon is absorbed and the electron gets scattered done clear
  C)
  The photon is not absorbed. It gets scattered. done clear
  D)
  None of the above done clear
  View Solution play_arrow

• question_answer3)
  How the corresponding wavelength of the absorbed photon is represented in the absorption spectrum?
  A)
  By a black line done clear
  B)
  By a white line done clear
  C)
  By a black line in the lower wavelength range and by a white line in the higher wavelength range done clear
  D)
  By a white line in the lower wavelength range and by a black line in the higher wavelength range done clear
  View Solution play_arrow

• question_answer4)
  What should be the concentration of metal for analysis using Atomic Absorption Spectrometer?
  A)
  Very High concentration done clear
  B)
  Very Low concentration done clear
  C)
  Medium concentration done clear
  D)
  Any concentration done clear
  View Solution play_arrow

• question_answer5)
  How the sample for analysis is driven to atomic state in AAS?
  A)
  At a very high temperature, the sample is driven to its gaseous state done clear
  B)
  Using an atomizer and then intense heating. done clear
  C)
  By rotating the solution of the sample at a very high speed, done clear
  D)
  None of the above done clear
  View Solution play_arrow

• question_answer6)

  Directions Q. 6 to 10: Read the following text and answer the following questions on the basis of the same:

  Spectrum Analysis and Astronomy

  Each element in the periodic table can appear in gaseous form and produce its own spectrum unique to that element. Hydrogen will not look like Helium, which will not look like carbon which will not look like iron... and soon.

  Astrophysists can identify what kinds of materials are present in stars from the analysis of star's spectra. This type of study is called astronomical spectroscopy.

  The science of spectroscopy is quite sophisticated.

  From spectrum lines analysis astrophysists can determine not only the element, but the temperature and density of that element in the star. The spectral line also can tell us about any magnetic field of the star.

  The width of the line can tell us how fast the material is moving. We can learn about winds in stars from this. The shifting of spectral lines shift back and forth indicates that the star may be orbiting another star.

  The following table shows a rough guide for the relationship between the temperature of a star and the electromagnetic spectrum.

  Temperature (Kelvin) Predominant radiation Astronomical Examples 600 K Infrared Planets, warm dust 6,000 K Optical The photosphere of Sun and other stars 60,000 K UV The photosphere of very hot stars 600,000 K Soft X-rays The corona of the Sun 6,000,000 K X-rays The coronae of active stars

  If the spectrum of a star is red or blue shifted, then it can be used to infer its velocity along the line of sight. Edwin Hubble observed that more distant   galaxies tended to have more red shifted spectra.

  This establishes the theory of expansion of the universe.

  What is astronomical spectroscopy?
  A)
  Study of spectrum of star light and to identify its distance from Earth. done clear
  B)
  Study spectrum of star light and to identify what kinds of elements are present in stars. done clear
  C)
  Both (a) and (b) done clear
  D)
  None of the above done clear
  View Solution play_arrow

• question_answer7)
  From the spectrum analysis the following information of a star can be obtained.
  A)
  Elements present, temperature done clear
  B)
  magnetic field, density, mass done clear
  C)
  distance of the star done clear
  D)
  Both (a) and (b) done clear
  View Solution play_arrow

• question_answer8)
  The lines in a star's spectrum is found to shift back and forth. What conclusion may be drawn from this observation?
  A)
  The star may be orbiting another star done clear
  B)
  There may be a storm in the star done clear
  C)
  The star may be rotating at a very high speed done clear
  D)
  None of the above done clear
  View Solution play_arrow

• question_answer9)
  What may be the approximate temperature if soft X-rays are found predominantly in the spectrum?
  A)
  60000 C done clear
  B)
  600000 C done clear
  C)
  60000 K done clear
  D)
  600000 K done clear
  View Solution play_arrow

• question_answer10)
  Which nature of spectrum establishes the theory of the expanding universe?
  A)
  Red-shift of spectrum done clear
  B)
  Blue-shift of spectrum done clear
  C)
  Back and forth movement of spectral lines done clear
  D)
  None of the above done clear
  View Solution play_arrow