Diagnostic Test

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Diagnostic Test
The diagnostic test is meant to check some basic
fundas to see if you are ready for this course.
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• What is the fundamental constituent of the matter
  we see around? (we are not referring to the
  fundamental particles!)

Atoms (diamond is made carbon atoms), Ions
(common salt is made of Na and Cl ions,
Molecules (ice is made of H2O molecules).

• What kinds of bonds exist?

The strong bonds are Covalent, ionic and
metallic bonds. The weak interactions include
hydrogen bond and Van der Walls bond.

• What are the states of matter? How can change in
  state be brought about?

Solid, liquid and gas. Change in state can be
brought about by temperature and pressure.

• In metals the electrical conduction takes place
  by________.

Motion of free electrons.

• In ionic solids electrical conduction takes
  places by ______.

Motion of cations (vacancies are needed for this)

• Which of the following bonds has a more
  directional character covalent, ionic,
  metallic?

Covalent bonds are directional.

• Temperature is a measure of _______________.

The average kinetic energy of the molecules.

• Which of the two has an ordered structure
  crystal or glass.

Crystal. Glasses may have short range order but
no long range order.

• Is a Cu wire a single crystal?

Cu wire is made of crystalline regions called
grains. It is a polycrystal.
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• What properties of electromagnetic radiation will
  make ideal diffraction possible?

(i) monochromatic source, (ii) coherent
radiation, (iii) wavelength of the order of
lattice spacing.

• What can happed if waves impinge on a material?

Reflection, transmission, absorption. A
combination of these may also occur.

• What is a vector?

A vector, unlike a scalar has both direction and
magnitude. In 3 dimensions a vector is specified
by 3 numbers.

• Can we have perfect crystals?

Crystals can have many defects. 3 of these are
unavoidable Surface, thermal vibration of atoms,
vacancies.

• Why are X-rays used for study of materials?

X-rays have wavelength of the order of lattice
spacing and can be used for diffraction studies
to determine crystal structures.

• What happens to the internal energy of water when
  we heat it?

The internal energy (E) increases due to increase
in translational, rotational and vibrational
kinetic energy of water molecules.

• What are the basic properties associated with an
  electron?

An electron has mass, charge, spin (and hence
angular momentum and magnetic moment).
In spite of having the properties mentioned
above, the electron is nearly a point
(pointlike)- no known dimension to 10?15m.

• How big is an electron?

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• What is the difference between a insulator and a
  semi-conductor?

Both have bandgaps. The semiconductor has a small
bandgap, such that even at room temperature some
electrons can be excited across the bandgap.

• Give examples of semiconductors.

Ge, Si, GaAs, GeSi (they can be elements or
compounds).

• What is a hole?

A hole is the vacant state in the valence
(energy) band of a semiconductor, when a electron
is excited to the conduction band (should not be
confused with a vacancy).

• If Fe is a ferromagnetic material, why is a
  sample of Fe non-magnetic (unless magnetized)?

The regions where magnetic spins are arranged
in parallel are called domains. The domains are
arranged in such a way as to give a minimum
external magnetic field.

• If microscopy is done with red light or blue
  light- which one of the two illuminations will
  give better resolution?

Blue light with a shorter wavelength, will give a
better resolution.

• Electrical conductivity of metals will increase
  or decrease with T?

Decrease. Electrons will be scattered more by
lattice vibrations. Hence a nearly perfect
crystal will become a superconductor at 0K.

• How many dimensions does space have?

3D. But in materials science we often deal with
lower dimensional objects which are effectively
2D, 1D and 0D. Sometimes even with higher
dimensions!
Certain arrangement of spheres give a highest
volume occupied by matter (of 74). Crystals
which have this kind of packing are called close
packed crystals.

• What are close packed crystals?

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