Q 1.A uniform silver wire has a resistivity of 1.54 × 10^-8 ohm-m at room temperature. For an electric field along the wire of 1 volt/cm, calculate the average drift velocity of electron assuming that there are 5.8 × 10^28 conduction electrons/m^3 . Also calculate the mobility.
Q. 2. Calculate the drift velocity of the free electrons with a mobility of 3.5 × 10^-3 m^2V^-1s^-1 in copper for an electric field strength of 0.5 V/m.
Q 3. Resistivity of copper is 1.73 × 10^-8 m. Its density is 8.92 × 10^3 kg/m^2 and atomic weight is 63.5 Assuming classical laws , calculate the mobility of electrons.
Q 4.Use the Fermi distribution function to obtain the value of F(E) for E-EF =0.01 eV at 200 K.
Q5. The electrical resistivity of Cu at 27˚ C is 1.72×10^-8 ohm-m. Compute its thermal conductivity if the Lorentz number is 2.26×10^-8WohmK-2.
Unit II Semiconducting Materials
Q. 1. A semiconducting crystal 12 mm long, 5mm wide and 1mm thick has a magnetic flux density of 0.5 Wb/m^2 applied from front to back perpendicular to largest faces. When a current of 20mA flows length wise through the specimen , the voltage measured across its width is found to be 37μV. What is the Hall coefficient of this semiconductor.
Q 2.For an intrinsic semiconductor with a band gap of 0.7 eV, determine the position of EF at T= 300K if m*h=6m*e.
Q 3.The intrinsic carrier density at room temperature in Ge is 2.37×10^19/m^3. If the electron and the hole mobilities are 0.38 and 0.18 m^2V^-1s^-1 respectively . Calculate its resistivity.
Q 4.Calculate the intrinsic concentration of charge carriers of Ge at 300K. Eg for Ge is 0.67 eV. Given ( m*e/m*o=0.12 and m*h/m*o=0.28.)
Q 5.The mobilities of electrons and holes in a sample of intrinsic Ge at 300K are 0.36 m^2V^-1s^-1 and 0.17m^2V^-1s^-1 respectively. Find the forbidden energy gap, if the resistivity of the specimen is 2.12 m.
Unit III Magnetic materials :
1. A paramagnetic material has a magnetic field intensity of 10^4 A/m. If the susceptibility of the material at room tmeprature is 3.7 x 10^-3, calculate the magnetization and flux density in the material.
2. The critical temperature for a metal with isotopic mass 199.5 is 4.185K. Calculate the isotopic mass if the critical temperature falls to 4.133K.
3. The superconducting transition temperature of lead is 7.26K. The initial field at 0K is 64x10^3 A/m. Calculate the critical field at 5 K.
4. The magnetic field intensity of a ferric oxide piece is 10^6 A/m. If the susceptibility of the material at room temperature is 1.5 x 10^-3, calculate the flux density and magnetization of the material.
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