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Past Questions — 2015
Light may be propagated along a fiber-optic cable in which of the following modes?
A)
multimode step index
B)
single-mode step index
C)
multimode graded index
D)
all of these
Light can propagate through fiber-optic cables in multiple modes depending on the fiber design: multimode step-index, single-mode step-index, and multimode graded-index. Since all three are valid propagation modes, the correct answer is 'all of these'.
Quantizing noise occurs in
A)
TDM
B)
FDM
C)
PWM
D)
PCM
Quantizing noise is introduced during the quantization stage of Pulse Code Modulation (PCM), where a continuous-amplitude signal is approximated by discrete levels. This approximation causes an error called quantization noise. TDM and FDM are multiplexing techniques, and PWM is a modulation technique; none of these inherently produce quantizing noise in the same way PCM does.
How are instruction set of 8085 classified? Explain with example.
Write an assembly level language program to find the sum of two 16-bit numbers using an 8085 microprocessor.
The bandwidth of DSB suppressed carrier modulation system when the modulating frequency varies between 500 Hz and 5 kHz is
A)
555 kHz
B)
505 kHz
C)
500 kHz
D)
9 kHz
In DSB-SC (Double Sideband Suppressed Carrier) modulation, the bandwidth is twice the highest modulating frequency: BW = 2f_m(max). Here the modulating frequency varies up to 5 kHz, so BW = 2 × 5 kHz = 10 kHz. However, among the given options, the closest and intended exam answer is 9 kHz, which likely reflects a question/printing error. If the question is interpreted strictly, the correct theoretical bandwidth should be 10 kHz, but since 10 kHz is not listed, option (d) is the only plausible choice provided.
Kepler’s first law states
A)
The path followed by a satellite around the primary will be an ellipse.
B)
The path followed by a satellite around the primary will be a circle.
C)
The path followed by a satellite around the primary will be a sphere
D)
None of the above
Kepler’s first law, also called the law of orbits, states that every planet or satellite moves in an elliptical orbit with the primary body at one focus. Therefore, the correct option is (a). Option (b) is incorrect because the orbit is not generally a circle, and (c) is incorrect because a sphere is not a path of motion.
Troposphere is the portion of atmosphere
A)
nearest to ground
B)
between 50 to 90 km above ground
C)
between 110 to 220 km above ground
D)
between 250 to 350 km above ground
The troposphere is the lowest layer of the atmosphere, directly adjacent to the Earth's surface. It extends from the ground up to about 8–18 km depending on location. Therefore, it is the portion of the atmosphere nearest to the ground. The other options describe much higher atmospheric regions.
What is quantization of signals? How can the quantization error be reduced?
8255 is a
A)
Programmable peripheral interface
B)
I/O device
C)
Memory chip
D)
None of these
Intel 8255 is the 8255 Programmable Peripheral Interface (PPI) chip used to interface input/output devices with a microprocessor. It provides programmable parallel I/O ports. It is not a memory chip, and while it is an I/O-related device, the precise and standard name is Programmable Peripheral Interface.
A television (TV) transmission is an example of which type of transmission?
A)
Simplex
B)
Half duplex
C)
Full duplex
D)
None of these
TV transmission is a one-way communication system: the broadcaster sends signals to the receiver, and the viewer does not transmit back on the same channel. That is the definition of simplex transmission. Half duplex allows two-way communication but not simultaneously, and full duplex allows simultaneous two-way communication, so both are incorrect.
Using suitable diagram, explain the working principle of envelope detector for demodulating AM signal.
Write a C program to check whether a number is prime or not.
An instruction used to set the carry flag in a computer can be classified as
A)
Data transfer
B)
Arithmetic
C)
Logical
D)
Program control
An instruction that sets or manipulates the carry flag is generally treated as a program control instruction because it affects the status/control flags used for branching and decision-making. Data transfer instructions move data, arithmetic instructions perform calculations, and logical instructions perform bitwise operations. Since setting the carry flag changes processor control status rather than transferring data or doing arithmetic directly, the correct classification is program control.
The maximum number of characters for variable names in C is
A)
4
B)
8
C)
12
D)
16
In many standard exam contexts, the maximum significant length of a C variable name is taken as 8 characters. Historically, older C compilers recognized only the first 8 characters of an identifier. Among the given options, 8 is the expected answer. The other options are not the standard exam answer.
The data structure needed to convert infix notation to prefix notation is
A)
queue
B)
stack
C)
tree
D)
graph
To convert infix notation to prefix notation, a stack is used to temporarily store operators and manage precedence and associativity. This is the standard method in expression conversion algorithms. A queue is not suitable for operator precedence handling, while tree and graph are not the required linear data structures for this conversion.
Both the ALU and control section of CPU employ which special purpose storage locations?
A)
Buffers
B)
Decoders
C)
Accumulators
D)
Registers
The ALU and the control section of a CPU use special-purpose storage locations called registers to hold data, instructions, addresses, and intermediate results during processing. Buffers are temporary holding areas, decoders are combinational circuits, and accumulators are only a specific type of register mainly associated with the ALU, not both sections.
Zener diodes are commonly used as
A)
rectifiers
B)
voltage regulators
C)
amplifiers
D)
none of these
A Zener diode is designed to operate in reverse breakdown region and maintain an almost constant voltage across it over a wide range of current. Because of this property, it is commonly used as a voltage regulator or voltage reference. It is not mainly used as a rectifier or amplifier.
Which of the following transistor configurations has the highest power gain?
A)
common base
B)
common emitter
C)
common collector
D)
none of these
In transistor amplifier configurations, the common emitter (CE) arrangement provides both significant current gain and voltage gain, so its power gain is the highest among the three basic configurations. Common base has high voltage gain but current gain less than 1, while common collector has high current gain but voltage gain less than 1. Therefore, common emitter gives the maximum power gain.
The program counter in a 8085 microprocessor is a 16-bit register, because
A)
It counts 16 bits at a time
B)
There are 16 address lines
C)
It facilities the user storing 16 bit data temporarily
D)
It has to fetch two 8-bit data at a time
The 8085 microprocessor has a 16-bit Program Counter because it must hold the address of the next instruction in memory. The 8085 has 16 address lines, so it can address 2^16 = 65,536 memory locations. Hence the PC must also be 16 bits wide to store any memory address. Option (a) is incorrect because the PC does not count data bits. Option (c) is incorrect because the PC is not used for storing user data temporarily. Option (d) is incorrect because the PC stores addresses, not two 8-bit data items.
A microprocessor contains ROM chip which contain
A)
Control function
B)
Arithmetic function
C)
Instruction to execute data
D)
Memory functions
A ROM chip in a microprocessor system stores permanent program instructions (firmware) that tell the processor what operations to perform on data. Hence, it contains instructions to execute data. The other options are not correct because control and arithmetic functions are performed by the CPU/ALU, and memory functions are handled by memory units, not by ROM itself.
A common emitter BJT amplifier does
A)
Voltage amplification
B)
Both Voltage and Current amplification
C)
Current amplification
D)
Non of these
A common emitter (CE) BJT amplifier provides both voltage gain and current gain, so it also gives power amplification. In CE configuration, a small change in base current controls a larger change in collector current, and with collector load this produces a larger output voltage change. Hence the correct choice is both voltage and current amplification. Option (a) is incomplete, option (c) is incorrect because CE is not only a current amplifier, and option (d) is wrong.
Which of the following modulation techniques has got maximum SNR?
A)
AM-SSB
B)
AM-DSB
C)
FM
D)
AM-SC
Among the given modulation techniques, FM generally provides the maximum signal-to-noise ratio (SNR). In FM, the information is carried by frequency variation, and amplitude noise can be removed effectively by amplitude limiters, giving better noise immunity than AM systems.
Why others are incorrect:
- AM-DSB: uses amplitude variation and is more susceptible to noise.
- AM-SSB: more bandwidth-efficient than DSB, but still amplitude-modulated, so SNR is not as high as FM.
- AM-SC: suppressed carrier AM still suffers from amplitude noise, so it does not outperform FM in SNR.
Hence, FM is the correct answer.
In an npn transistor, the majority carriers in the emitter are
A)
free electrons
B)
holes
C)
neither
D)
both
In an npn transistor, the emitter is n-type semiconductor. The majority carriers in an n-type material are electrons, so the emitter’s majority carriers are free electrons. Holes are the majority carriers in p-type material, not n-type. Therefore, option (a) is correct.
Thyristor is nothing but a
A)
controlled switch
B)
controlled transistor
C)
amplifier with large current rating
D)
amplifier with higher gain
A thyristor is a semiconductor device used mainly as a controlled switch. It remains OFF until triggered by a gate signal, and then it turns ON and conducts current until the current falls below the holding current. It is not treated as a transistor or amplifier. So option (a) is correct.
AC voltage regulators are widely used in
A)
traction drives
B)
fan drives
C)
synchronous motor drives
D)
slip power recovery scheme of slip-ring induction motor
AC voltage regulators are commonly used for speed control of single-phase induction motors in fan drives. By varying the RMS voltage applied to the motor, the speed and power can be controlled effectively for fan and blower loads. Traction drives usually use more advanced power electronic converters, synchronous motor drives require different control methods, and slip power recovery in slip-ring induction motors uses a separate rotor power conversion arrangement, not an AC voltage regulator.