PUBLIC SECTOR UNDERTAKING

PSU Study Materials

Electronics & Communication Engg.

Q.1.The impurity commonly used for realizing the base region of a silicon n-p-n transistor is

• Gallium
• Indium
• Boron
• Phosphorus

Q.2.An ideal op-amp is an ideal

• voltage controlled current source
• voltage controlled voltage source
• current controlled current source
• current controlled voltage source

Q.3.Voltage series feedback (also called series shunt feedback) results in

• increase in both input and output impedance
• decrease in both input and output impedance
• increase in input impedance and decrease in output impedance
• decrease in input impedance and increase in output impedance

Q.4.The Fourier transform of a conjugate symmetric function is always

• imaginary
• conjugate anti-symmetric
• real
• conjugate symmetric

Q.5.An AM signal and a narrow-band FM signal with identical carriers, modulating signals and modulation indices of 0.1 are added together. The resultant signal can be closely approximated by

• broadband FM
• SSB with carrier
• DSB-SC
• SSB without carrier

Q.6.Consider a lossless antenna with a directive gain of +6db. If 1mW of power is fed to it the total power radiated by the antenna will be

• 4mW
• 1mW
• 7mW
• 1/4mW

Q.7.The minimum number of flip-flops required to construct a mod-75 counter is

• 5
• 6
• 7
• 8

Q.8.A ‘literal’ in Boolean Algebra means

• a variable inn its uncomplemented form only
• a variable ORed with its complement
• a variable in its complemented form only
• a variable in its complemented or uncomplemented form

Q.9.The number of control lines for a 8:1 multiplexer is

• 2 
• 3 
• 4
• 5

Q.10.The 8085 assembly language instruction that stores the content of H and L registers into the memory locations 2050H and 2051H, respectively, is

• SPHL 2050H
• SPHL2051H
• SHLD 2050H
• STAX 2050H

Q.11.The insulation strength of an EHV transmission line is mainly governed by

• load power factor
• switching over-voltages
• harmonics
• corona

Q.12.For the equation, s3 – 4s2+ s + 6 = 0 the number of roots in the left half of s-plane will be

• 0
• 1
• 2
• 3

Q.13.In a DMA write operation the data is transferred

• from I/O to memory.
• from memory to I/O.
• from memory to memory.
• from I/O to I/O.

Q.14.Pseudo instructions are basically

• false instructions.
• instructions that are ignored by the microprocessor.
• assembler directives.
• instructions that are treated like comments.

Q.15.What will be the contents of register AL after the following has been executed
MOV BL, 8C
MOV AL, 7E
ADD AL, BL

• 0A and carry flag is set
• 0A and carry flag is reset
• 6A and carry flag is set
• 6A and carry flag is reset

Q.16.The most commonly used amplifier in sample & hold circuits is

• A unity gain non-inverting amplifier
• A unity gain inverting amplifier
• An inverting amplifier with a gain of 10
• An inverting amplifiers with a gain of 100

Q.17.If the Laplace transform of f (t ) is (w/(s2+w2),) then the value of Lim f (t ),where t tends to infinity

• cannot be determined.
• is zero.
• is unity.
• is infinity

Q.18.The auto-correlation function of a rectangular pulse of duration T is

• a rectangular pulse of duration T.
• a rectangular pulse of duration 2T.
• a triangular pulse of duration T.
• a triangular pulse of duration 2T.

Q.19.The FT of a rectangular pulse existing between t = -T / 2 to t = T / 2 is a

• sine squared function.
• sine function.
• sine squared function.
• sine function.

Q.20.Kirchoff’s law of voltages states that in a complete circuit,

• The sum of voltage decreases equals the sum of voltage increases.
• All paths in a circuit have equal voltage increases.
• All electrons must travel the same path.
• Electrons provide the necessary voltage for the circuit to operate.
• The voltage is equal to the energy divided by the current.

Q.21.In relation to the synchronous machines, which one of the following statements is false?

• In salient pole machines, the direct-axis synchronous reactance is greater than the quadrature-axis synchronous reactance
• The damper bars help the synchronous motor self start
• Short circuit ratio is the ratio of the field current required to produce the rated voltage on open circuit to the rated armature current
• The V-curve of a synchronous motor represents the variation in the armature current with field excitation, at a given output power

Q.22.When a step-input is given to an op-amp integrator, the output will be

• a ramp.
• a sinusoidal wave.
• a rectangular wave.
• a triangular wave with dc bias.

Q.23.The reverse – saturation current of a silicon diode

• doubles for every 10°C increase in temperature
• does not change with temperature
• halves for every 1°C decrease in temperature
• increases by 1.5 times for every 2°C increment in temperature

Q.24.The maximum possible collector circuit efficiency of an ideal class A power amplifier is

• 15%
• 25%
• 50%
• 75%

Q.25.When a sinusoidal voltage wave is fed to a Schmitt trigger, the output will be

• triangular wave.
• asymmetric square wave.
• rectangular wave.
• trapezoidal wave.

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