1. The electron drift mobility in silver has been measured to be 54 cm2 V−1 s−1 at 27 °C. The atomic
mass and density of Ag are given as 107.87 amu or g mol−1 and 10.50 g cm−3, respectively. (a)
Assuming that each Ag atom contributes one conduction electron, calculate the resistivity of
Ag at 27 °C. Compare this value with the measured value of 1.6 × 10 −8 Ωm at the same
temperature and suggest reasons for the difference. (b) Calculate the thermal conductivity of
silver at 27 °C and at 0 °C.
2. The following data are known for copper: (i) Density = 8.92 x 103 kg/m3, (ii) Resistivity of
copper = 1.73 x 10-8 .m, (iii) Atomic weight = 63.5. Calculate the mobility and the average
time of collision of the electrons in copper obeying classical laws.
3. Given that the Fermi energy of copper is 7 eV at room temperature, what is the number of
electrons per unit volume with energy greater than 8 eV?
4.
A copper wire has resistivity of 1.7 x 10-8 .m at room temperature of 300 K. If the copper is
highly pure, find the resistivity at 700C.
5. An alloy of metals is found to have resistivity of 1.2 x 10-6 .m at 300 K. When it is heated to
a temperature of 700C, the resistivity is found to increase by 11%. Assuming Matthiessen’s
rule to hold good for the alloy, find its resistivity due to impurity scattering alone.
6. An electric field of 1000 V/m is applied across a Ge sample at 300 K. Show that the carrier drift
velocity is very small compared to its thermal velocity (mn* = 0.037 m and n = 0.39 m2/V.s).
7. A 0.01 m bar of n-type Ge (mn* = 0.45 m) with an electron mobility of 0.39 m2V-1s-1 is connected
to a power supply of 50 V. (i) How long will the electrons take to drift the full length of the
bar? (ii) On an average how many collisions will an electron suffer during one transit? (iii)
What is the total energy received by the electron from the field and lost to the lattice?
8. The resistivity and the Hall coefficient of pure aluminum and Al with 1 at.% Si have been
measured at 20 °C (293 K) as ρ = 2.65 μΩ cm, RH = −3.51 × 10−11 m3 C−1 for Al and ρ = 3.33 μΩ
cm, RH = −3.16 × 10−11 m3 C−1 for 99 at.% Al -1 at% Si. The lattice parameters for the pure metal
and the alloy are 0.4049 nm and 0.4074 nm. What does the simple Drude model predict for
the drift mobility in these two metals? How many conduction electrons are there per atom?
9. Explain the terms : (i) magneto-crystalline anisotropy and (ii) magneto-crystalline anisotropy
energy.
10. A parallel plate capacitor using a dielectric material having an r of 2.2 has a plate spacing of
2 mm. If another material having a dielectric constant of 3.7 is used and the capacitance is to
be unchanged, what must be the new spacing between the plates?