List of top Material Science and Technology Questions

Two thigh bones (femurs) of $10 \ cm^2$ area support a 40 kg body. Average pressure is:
The resistivity of copper metal is \(1.7 \times 10^{-8} \, \Omega \, \text{m}\) and the atomic density of copper is \(8.5 \times 10^{28} \, \text{atoms/m}^3\). The collision time \(\tau\) for electrons in copper is:
Metallic sodium crystallizes in a BCC cubic form with a cube length of \(4.25 \times 10^{-10} \, \text{m}\). The concentration of conduction electrons is:
The kinetic energy of a 3-dimensional gas of \(N\) free electrons at 0 K is:
If the Madelung Constant of NaCl is 1.748, the equilibrium bond distance is \(2.018 \, \text{\AA}\), and the repulsion exponent is \(0.32 \, \text{\AA}\), the cohesive energy of NaCl is:
The ratio of charge carrier densities in a pure silicon crystal at \(27^\circ \text{C}\) and \(57^\circ \text{C}\) is 1.25. The energy gap of the semiconductor is:
The probability that a state is filled at the conduction edge \((E_c)\) is precisely equal to the probability that a state is empty at the valence band edge \((E_v)\). The Fermi level is located at:
A pure silicon crystal has \(5 \times 10^{28} \, \text{atoms/m}^3\). It is doped with \(1 \, \text{ppm}\) concentration of pentavalent As. The number of holes is:
The concentration of hole-electron pairs in pure silicon at 300 K is \(7 \times 10^{15} \, \text{m}^{-3}\). Antimony is doped into silicon in proportions of \(1 \, \text{atom per} \, 10^7 \, \text{atoms}\), and half of the impurity atoms contribute electrons. The factor by which the number of charge carriers increases due to doping is:
The electron and hole mobilities in a silicon sample are \(0.135 \, \text{m}^2/\text{V·s}\) and \(0.048 \, \text{m}^2/\text{V·s}\), respectively. If the intrinsic carrier concentration is \(1.5 \times 10^{16} \, \text{atoms/m}^3\), the conductivity at 300 K is:
The lowest energy of an electron confined to a 3-dimensional box of length \(0.5 \, \text{\AA}\) is:
A uniform silver wire has a resistivity of \(1.54 \times 10^{-8} \, \Omega \, \text{m}\) at room temperature. When an electric field along the wire is \(1 \, \text{V/m}\), the drift velocity is:
The mean free path of conduction electrons in copper is about \(4 \times 10^{-8} \, \text{m}\). For a copper block, the electric field which can give on average \(1 \, \text{eV}\) energy to a conduction electron is:
The energy of a photon of sodium light (\(\lambda = 589 \, \text{nm}\)) is equal to the band gap of a semiconducting material. The minimum energy required to create a hole-electron pair is:
A semiconductor has acceptor levels \(57 \, \text{meV}\) above the valence band. The maximum wavelength of light which can excite an electron is:
A load of \(4.0 \, \text{kg}\) is suspended from a ceiling through a steel wire of length \(20 \, \text{m}\) and radius \(2.0 \, \text{mm}\). The length of the wire increases by \(0.031 \, \text{mm}\) at equilibrium. The Young’s modulus of steel is: (Take \(g = 9.81 \, \text{m/s}^2\)):
Two liters of an ideal gas at a pressure of 10 atm expands isothermally into a vacuum until its total volume is 10 liters. The heat absorbed during the process is:
A bar magnet made of steel has a magnetic moment of \(2.5 \, \text{Am}^2\) and a mass of \(6.6 \times 10^{-2} \, \text{kg}\). If the density of steel is \(7.9 \times 10^3 \, \text{kg/m}^3\), the intensity of magnetization of the magnet is:
An ideal solenoid with 40 turns per cm has an aluminium core and carries a current of 2.0 A. The magnetization I developed in the core and the magnetic field B at the center are:(Susceptibility of aluminium \(\chi = 2.3 \times 10^{-5}\)):
The maximum value of permeability \(\mu = 0.126 \, \text{T m/A}\). The maximum relative permeability \(\mu_r\) is:
The percentage increase in magnetic field \(B\) when the space within a current-carrying toroid is filled with aluminium is: (Susceptibility of aluminium \(\chi = 2.4 \times 10^{-5}\)):
A 0.500-inch diameter aluminum bar is subjected to a force of 2500 lb. The engineering stress in pounds per square inch (psi) on the bar is:
A 1.25 cm diameter bar is subjected to a load of 2500 kg. Calculate the engineering stress on the bar in megapascals (MPa):
Aluminium alloy after failure has a final length of 2.195 in and a final diameter of 0.398 in at the fractured surface. The percentage of elongation and reduction in area is:
A load of \(4.0 \, \text{kg}\) is suspended from a ceiling fan through a steel wire of radius \(2.0 \, \text{mm}\). The tensile stress developed in the wire when equilibrium is achieved is: (Take \(g = 9.81 \, \text{m/s}^2\)):