Uttar Pradesh Technical University (UPTU) 2007-2nd Sem B.Sc Electronics & Communication Systems B.tech 2006- BASIC ELECTRONICS - Question Paper
Printed Pages : 3 EC - 201
(Following Paper ID and Roll No. to be filled in your Answer Book)
IroII No.
B. Tech.
(SEM. II) EXAMINATION, 2006-07 BASIC ELECTRONICS
[Total Marks : 50
Time : 2 Hours]
Note : (1) All questions are compulsory.
(2) Assume suitable data wherever necessary.
Answer any four of the following :
3.5x4=14
Define resistivity, bulb resistance and ohmic contact resistance.
(a)
(b)
In an n-type Si, the fermi level is 0.3 eV. below the conduction band edge. Find the electron and hole concentrations in Si at room temperature (300 K) (for Si, Eg = l.leV, ni = 1.5 x 1010 per cm3 and h = 8.62 x 10"5 eV/K).
Assuming n= ND+ show that at very low temperatures, the Fermi level in an n-type semiconductor is given
(c)
2 Nf
KT
In
by
N
D
Ec+Ed
EjT? = -1-
(d) Differentiate between direct and indirect semiconductors.
(e) The intrinsic carrier concentration for Si at room temperature is 1.5 x 10+1 cm"3. The electron mobility for intrinsic silicon is 1350 cm2/Vs and hole mobility is 480 cm2/Vs. Calculate the resistivity of intrinsic Si at room temperature.
(1) Show that Lp is the average distance travelled by diffusing carriers before they recombine. The variable Lp represents the distance at which the excess hole concentration falls to 1/e of its value at the point of injection of an n-type semiconductor, (all notations carry standard meaning)
Answer any three of the following : 5x3=15
(a) The FB junction of an npn transistor is forward biased by VBF while the collector terminal is left open. What is the value of VCE at this point?
(b) Derive formula for transistor power dissipation. Obtaining this relationship where on the load line you would expect the power dissipation to the maximum?
(c) Describe the differences between re and hybrid equivalent model for a BJT.
(d) Derive the expressions for stability of BJT amplifiers.
(e) When a transistor is in saturation and IB is fixed, show that for small values of VCE (< 0.2V), VBE increases and VBC reduces with increase in VCE.
(a) Convert binary numbers 10111011 and 1101.0110111 into octal numbers.
(b) Convert 3F29 hexadecimal to its decimal equivalent.
(c) What are open-collector gates? Explain.
(d) Elucidate universal gates with the help of suitable example.
(e) How bases are converted in number systems?
What will be 2s complement representation of decimal - 14 into its equivalent hexadecimal?
Answer any two of the following : 4.5x2=9
(a) Explain, how does the frequency of the input signal to an op. amp affects voltage gain.
(b) Explain chopped and alternate methods of trace development of CROS. How many cycles of a 2-kHZ simusoidal signal are viewed if the sweep frequency is lkHZ.
(c) Draw circuit diagram of a multimeter and explain its operation in detail.
V-3035] 3 [ 1865 ]
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