Semi Conductors and Magnetic Materials Mid - I, September - 2014

1.Which of the following statements about electrical conduction in nearly pure materials is true?
  • At low temperatures, resistivity decreases to zero as the lattice no longer interferes with electron motion.
  • At low temperatures, conductivity decreases to a minimum based on residual lattice defects.
  • Dislocations and grain boundaries provide a low resistance route for electrons to travel through a material.
  • At higher temperatures, the scattering effect of thermal phonons swamps that of residual lattice defects.
Answer: D
2.Which of these is the correct order in terms of best to worst electrical conductivity (assumed pure materials) ?
  • Nb3Sn at 4K, Ag at 300K, Au at 300K, Nb3Sn at 300K, Cu at 300K.
  • Nb3Sn at 4K, Ag at 300K, Cu at 300K , Au at 300K, Nb3Sn at 300K.
  • Nb3Sn at 4K, Cu at 300K, Nb3Sn at 300K, Ag at 300K, Au at 300K.
  • Ag at 300K, Cu at 300K, Nb3Sn at 4K , Au at 300K, Nb3Sn at 300K.
Answer: B
3.What characteristic clearly distinguishes semiconductors from metals and nonmetals?
  • Luster
  • electrical conductivity
  • ductility
  • thermal conductivity
Answer: B
4.What explains why semiconductors have different electrical properties from metals?
  • more valence electrons
  • fewer valence electrons
  • band gap structure
  • no differences.
Answer: C
5.Naturally occurring magnets in nature are called
  • plastic
  • stones
  • Iodestones
  • metals
Answer: C
6.Which electronic devices are primarily made from semiconductors?
  • transistors
  • resistors
  • capacitors
  • none of the above
Answer: A
7.The readiness of the material to accept the magnetism is expressed by its:
  • permeability
  • permittivity
  • Coercivity
  • Susceptibility
Answer: A
8.Hard Magnetic Materials are suitable for manufacture of:
  • Relays
  • transformer cores
  • Permanent Magnets
  • reactor cores
Answer: C
9.The number of lines of force per unit area is the measure of:
  • Magnetic Field density
  • Magneto motive force
  • Magnetic susceptibility
  • Magnetic flux density
Answer: D
10.Magnetic Susceptibility is positive and very large in case of _______ materials:
  • paramagnetic
  • diamagnetic
  • ferro-magnetic
  • Anti-ferro magnetic
Answer: C
11.In a metallic conductor, are the valence shells filled, empty, ____________less than half filled.
Answer: Partially filled
12.Label each as C-conductor, SC semiconductor, or I- insulator, _______Copper wire _________Glass rod _________ Silicon chip.
Answer: C,I,SC
13.As one electron is promoted from the valence band to the conduction band, a __________ is formed in the valence band.
Answer: Hole
14.The _________ is the critical point where a material's intrinsic magnetic moments change direction.
Answer: Curie temperature
15.___________ is the basic mechanism by which certain materials (such as iron) form permanent magnets.
Answer: Ferromagnetism
16.__________ occurs in ferromagnetic materials and ferroelectric materials, as well as in the deformation of some materials (such as rubber bands and shape-memory alloys) in response to a varying force.
Answer: Hysterisis
17.Ferro magnetic materials are generally used as ___________
Answer: Semiconductors
18.At ____________temperature are there no electrons in the conduction band of a semiconductor.
Answer: O ring
19.For current to flow through a diode, the positive terminal of the power supply must be connected to the ____________material.
Answer: p-type
20.Are electrons in the valence band of a semiconductor are in the bonding or anti bonding state? _________________
Answer: Bonding