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Eti 2104: Physical Electronics I Question Paper

Eti 2104: Physical Electronics I

Course:Bachelor Of Science In Telecommunication And Information Technology

Institution: Dedan Kimathi University Of Technology question papers

Exam Year:2014

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DEDAN KIMATHI UNIVERSITY OF TECHNOLOGY
University Examination 2013/2014
FIRST YEAR SECOND SEMESTER EXAMINATION FOR THE DEGREE IN BACHELOR OF
SCIENCE IN TELECOMMUNICATION AND INFORMATION ENGINEERING
ETI 2104: PHYSICAL ELECTRONICS I
DATE: 16TH APRIL 2014 TIME: 11.00 AM – 1.00 PM
INSTRUCTIONS
Question ONE is Compulsory. Answer Question one and any other two questions.
Take 12 7
0 0 ? 8.854 10 F /m, ? 4? 10 H /m ? ? ? ? ? ?
Electron mass 31 9.1 10 e m Kg ? ? ? , Electronic charge 19 e 1.6 10 C ? ? ?
Planck’s constant 34 h 6.625 10 Js ? ? ? , Boltzmann’s Constant 23 0 1 k 1.38 10 J K ? ? ? ?
1.
a) Describe Bohr’s atomic model [4 mks]
b) Determine the kinetic, potential and total energy of an electron revolving in Bohr’s first
orbit of a hydrogen atom [3 mks]
c) A copper wire of 2 mm diameter with conductivity of 5.8 x 107 S/m and electron mobility
of 0.0032 m2N - s is subjected to an electric field of 20 V/m. Determine
i. The charge density of free electrons
ii. The current density
iii. Current flowing in the wire
iv. The electron drift velocity [5 mks]
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d) Explain the physical significance of the Fermi energy? [2 mks]
e) With aid of suitable diagrams and mathematical derivations, show that the Fermi level in an intrinsic semiconductor lies between conduction and valence bands [6 mks]
f)
i) Define barrier potential. [1 mk]
ii) Determine the barrier potential at room temperature of a P-N junction in silicon which is doped to a carrier density of 1021 m-3 on the P-side and carrier density on N-side of 1022 m-3. The intrinsic carrier density for silicon is 1.4 x 1016 m-3 [3 mks]
g) Draw schematic symbols and well labeled characteristic curves for the following types of PN junction diodes
i. Ideal diode
ii. Zener diode
iii. Tunnel diode [6 mks]
2.
a) A germanium diode draws 40 mA with a forward bias of 0.25 V. The junction is at room temperature of 293 K. Determine the reverse saturation current of the diode. [2 mks]
b) With aid of energy band diagrams, explain the difference between insulators, conductors and semiconductor [6 mks]
c) Determine the resistance of a 47125 m length of round copper wire of a diameter 1 mm that given that the conductivity of copper is 60 MS/m. A cylindrical piece of silicon having a diameter 1 mm is doped with 1020 m-3 atoms of phosphorous which are fully ionized. Determine the length of this silicon that would be required to give equal resistance to the copper wire if the electron mobility in silicon is 0.1 m2/V-s [6 mks]
d) Explain the construction and operation of the PIN diode and list two typical applications of the diode [6 mks]
3.
a) Differentiate between Intrinsic and extrinsic semiconductors [2 mks]
b) Explain how doping modulates the energy gap in a P-type and N-type semiconductor material. [6 mks]
c) Determine the intrinsic carrier concentration and conductivity of silicon at 300 K given that the silicon constant, electron mobility, hole mobility and the band gap energy for silicon is 3 x 1025 m-3,0.14 m2V s , 0.05 m2V s , 1.1 eV respectively [6 mks]
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d) With the aid of well labeled diagrams, explain how temperature affects the conductivity of
intrinsic and extrinsic semiconductors. [6 mks]
4.
a) Briefly explain the Hall Effect phenomenon [2 mks]
b) A current of 50 A is passed through a metal strip, which is subjected to a magnetic flux of
density 1.2 Wb/m2. The magnetic field is directed at right angles to the current direction
and the thickness of the strip in the direction of magnetic field is 0.5 mm. Given that the
number of conduction electrons in the metal is 7.51 x 1021 m-3, determine the Hall voltage
[3 mks]
c) List any Four applications of Hall Effect [3 mks]
d) A uniform silver wire has a resistivity of 16 1.4 10 cm ? ? ? ? at room temperature. An electric
field of 50V/m exists along the length of the wire. If the number of free electrons is
5.8?1028 /m3 . Determine the conductivity of the wire, drift velocity of electrons and their
mobility.
[6 mks]
e) Explain the construction and operation of the Varactor diode and list two typical
applications of the diode [6 mks]
5.
a) With aid of diagrams, explain the construction and operation of the P-N junction diode
[4 mks]
b) Sketch and explain the forward and reverse V/I characteristic of the PN junction [4 mks]
c) P-N junction diode has a leakage current of 10-14 A at room temperature of 27 oC and 10-9 A
at 125 oC. The diode is forward biased with a constant current source of 1 mA at room
temperature. If current is assumed to remain constant, determine the junction barrier
voltage at room temperature and at 125 oC [6 mks]
d) Explain the following terms as applies to
i. Drift
ii. Diffusion
iii. Recombination [6 mks]

Eti 2104: Physical Electronics I Question Paper

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