← MES Jr. Grade
Past Questions
Which interrupt has the highest priority?
A)
INTR
B)
TRAP
C)
RST6.5
D)
RST7.5
In the 8085 microprocessor, TRAP is the highest-priority interrupt. It is non-maskable and cannot be disabled by software, so it is serviced before all other interrupts. INTR is the lowest-priority interrupt among the given options, while RST7.5 and RST6.5 are maskable vectored interrupts with lower priority than TRAP.
In a fully controlled converter the load voltage is controlled by which of the following quantity.
A)
Extension angle
B)
Firing angle
C)
Conduction angle
D)
None of these
In a fully controlled converter, the average load voltage is controlled by varying the firing angle (also called delay angle, α) of the thyristors. By delaying the triggering of the devices, the output DC voltage changes. Extension angle and conduction angle are not the primary control quantities in a fully controlled converter.
In FM, the noise can be further decreased by
A)
decreasing deviation
B)
increasing deviation
C)
keeping the deviation constant
D)
none of these
In FM, the effect of noise is reduced when the frequency deviation is made larger, because the signal becomes less sensitive to amplitude noise after limiting and detection. A larger deviation generally improves the signal-to-noise ratio. Hence, noise can be further decreased by increasing deviation. Option (a) is wrong because decreasing deviation reduces noise immunity. Option (c) is not the principle for noise reduction. Option (d) is incorrect because (b) is the correct choice.
Carrier signal has
A)
constant magnitude
B)
constant frequency
C)
variable frequency
D)
variable time
A carrier signal is a high-frequency sinusoidal wave used to transmit information. In standard communication systems, its frequency remains constant, while its amplitude, phase, or frequency may be varied by the message signal during modulation. Hence, the carrier signal has constant frequency. Option (a) is not generally correct because the carrier’s magnitude may be changed in AM; (c) describes a modulated signal in FM, not the carrier itself; and (d) is not a defining property.
A microprocessor with 12 address line is capable of addressing
A)
1024 locations
B)
2028 locations
C)
4096 locations
D)
64K locations
A microprocessor with 12 address lines can generate 2^12 unique addresses. Since 2^12 = 4096, it can address 4096 memory locations. Option (a) 1024 corresponds to 10 address lines, and (d) 64K corresponds to 16 address lines.
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, and the 8085 has 16 address lines. A 16-bit address can uniquely identify 2^16 = 65,536 memory locations. Option (a) is wrong because the PC does not count data bits. Option (c) is wrong because the PC is not used for temporary data storage. Option (d) is wrong because fetching 8-bit data is unrelated to why the PC is 16-bit.
In AM, the carrier is changed by a modulating signal. What parameter of the carrier is changed?
A)
amplitude
B)
frequency
C)
pulse width
D)
phase
In Amplitude Modulation (AM), the amplitude of the carrier wave is varied in accordance with the modulating signal, while its frequency and phase remain essentially constant. Hence, the correct answer is amplitude. Frequency corresponds to FM, phase to PM, and pulse width is related to pulse modulation techniques.
Which one of the following specifications is not correct for a common collector amplifier?
A)
High input impedance
B)
Low output impedance
C)
High voltage gain
D)
High current gain
A common collector amplifier (emitter follower) has high input impedance, low output impedance, and high current gain. Its voltage gain is approximately unity, not high. Therefore, 'High voltage gain' is the incorrect specification.
A photo diode works on the principle of
A)
photo-voltaic effect
B)
photo-conductive effect
C)
photo-electric effect
D)
photo-chemical effect
A photodiode operates mainly in reverse bias, and when light falls on it, electron-hole pairs are generated, increasing the conductivity of the junction. This is the photo-conductive effect. A photovoltaic effect is used in solar cells, photoelectric effect refers to emission of electrons from a material due to light, and photo-chemical effect involves chemical changes caused by light.
In a microprocessor, the bus which is used to transfer data from main memory to peripheral device is
A)
data bus
B)
input bus
C)
DMA bus
D)
output bus
The bus used to transfer data from main memory to a peripheral device is the output bus, because the data is moving out from memory/processor system toward an external device. The data bus is a general-purpose bidirectional bus used for transferring data both ways, while 'input bus' is not the standard term here. DMA refers to a transfer technique, not the specific bus name in this context.
An SCR is also called a
A)
triac
B)
thyristor
C)
diac
D)
unijunction transistor
An SCR (Silicon Controlled Rectifier) is a type of controlled semiconductor device commonly known as a thyristor. It is a four-layer, three-junction device used for switching and rectification. A triac is a bidirectional AC switch, a diac is a two-terminal trigger device, and a unijunction transistor is a different type of transistor used mainly for triggering circuits.
It is required to construct a counter to count up to 100(decimal). The minimum number of flip flops required to construct the counter is
A)
8
B)
7
C)
6
D)
5
A counter that counts up to 100 decimal must be able to represent at least 100 states. The minimum number of flip-flops n must satisfy 2^n >= 100. Since 2^6 = 64 is not enough and 2^7 = 128 is sufficient, the minimum required is 7 flip-flops. Hence, option (b) is correct.
The demodulation of the sound signals in a TV receiver is accomplished by
A)
linear detector
B)
product detector
C)
discriminator
D)
envelope detector
In a TV receiver, the sound signal is frequency-modulated (FM), so its demodulation is done by a discriminator (FM detector). A linear detector or envelope detector is used for AM signals, while a product detector is used for synchronous detection, not standard TV sound FM demodulation.
The reason of preferring FETs to bipolar transistors in integrated circuits is that
A)
they occupy very small space
B)
it has become a tradition
C)
fabrication of circuit is easy
D)
it is cheaper
FETs are preferred in integrated circuits mainly because they are very small in size and have high input impedance, so many devices can be packed on a chip. Among the given options, 'they occupy very small space' is the best reason. The other options are not the real technical reason: it is not due to tradition, cost alone is not the main factor, and while fabrication can be convenient, the key advantage is compactness and IC suitability.
A carrier is simultaneously modulated by two sine waves with modulation indices of 0.4 and 0.3. The resultant modulation index will be
A)
1.0
B)
0.7
C)
0.5
D)
0.35
For simultaneous modulation by two sine waves, the resultant modulation index is found by the root-sum-square method: m = √(m1² + m2²). Here, m1 = 0.4 and m2 = 0.3, so m = √(0.4² + 0.3²) = √(0.16 + 0.09) = √0.25 = 0.5. Hence, the correct answer is 0.5. The other options do not match this standard result.
The AM broadcast band is given by
A)
10 KHz to 30 KHz
B)
500 KHz to1500 KHz
C)
3 KHz to 30 MHz
D)
30 MHz to 300 MHz
The standard AM broadcast band lies in the medium-frequency range, approximately 530 kHz to 1700 kHz internationally, and commonly taught in exams as 500 kHz to 1500 kHz. Hence option (b) is correct. Option (a) is too low, option (c) is the HF range, and option (d) is the VHF range.
The effect of noise in a communication system is most adverse with reference to
A)
source
B)
channel
C)
encoder
D)
receiver
Noise is most harmful at the receiver because the receiver must detect, amplify, and recover the original message from the noisy signal. Any noise added in the channel ultimately affects the signal quality at the receiver, reducing SNR and causing errors in demodulation/decoding. The source and encoder do not directly suffer the adverse effect of channel noise, and the channel is the medium where noise is introduced, not where its effect is most critical.
PROM is
A)
permanent read only memory
B)
polarized read only memory
C)
positive read only memory
D)
programmable read only memory
PROM stands for Programmable Read Only Memory. It is a type of memory whose contents can be programmed once after manufacturing. The other options are incorrect because PROM does not mean permanent, polarized, or positive read only memory.
A common source FET amplifier has a load resistance RL = 500kΩ, rd = 100 kΩ and µ = 24. The voltage gain is
A)
30
B)
25
C)
20
D)
100
For a common source FET amplifier, the voltage gain is approximately A_v = μ(R_D || r_d) / r_d, or equivalently A_v = g_m(R_D || r_d). Here the load resistance is RL = 500 kΩ and the drain resistance is rd = 100 kΩ, so the effective load is the parallel combination: R = (500 × 100)/(500 + 100) kΩ = 83.33 kΩ. Using the given amplification factor μ = 24, the gain becomes A_v = μ × R / rd = 24 × 83.33 / 100 ≈ 20. Thus the correct answer is 20. The other options do not match the calculated gain.
The POS form of expression is suitable for circuit using
A)
XOR
B)
NAND
C)
AND
D)
NOR
POS means Product of Sums. A POS expression is naturally implemented using OR gates followed by an AND gate, but in universal-gate realizations it is especially suitable for NOR-based circuits because NOR is the dual of OR. Similarly, SOP is more suitable for NAND-based circuits. Therefore, the correct answer is NOR.
Output of the assembler in machine code is referred to as
A)
Object program
B)
Source program
C)
Macroinstruction
D)
Symbolic instruction
An assembler translates an assembly language source program into machine code. The machine-code output produced by the assembler is called the object program. A source program is the original assembly code, while macroinstruction and symbolic instruction are not the assembler’s machine-code output.
Eight memory chips of 32x4 bit size have their address buses connected together. What is the size of this memory system?
A)
512x2 bits
B)
256x4 bits
C)
64x16 bits
D)
32x32 bits
Each memory chip is 32×4 bits, meaning it has 32 addressable locations with 4 bits stored in each location. When 8 such chips have their address buses connected together, all chips respond to the same 32 addresses, so the number of locations remains 32. But the data width adds up: 8 chips × 4 bits = 32 bits per location. Therefore the total memory size is 32×32 bits. However, among the given options, the intended interpretation in such questions is usually that the chips are combined to increase depth and width in a standard way: 8 chips of 32×4 bits can be arranged as 64×16 bits only if grouped differently, but with address buses connected together the correct combined organization is 32×32 bits. Since that exact option is not present, the closest matching option given is (d).
The most highly doped region in a transistor is
A)
base
B)
collector
C)
emitter
D)
both emitter and collector
In a transistor, the emitter is the most heavily doped region because its job is to inject a large number of charge carriers into the base. The base is lightly doped and very thin, while the collector is moderately doped to collect carriers and withstand higher voltage. Therefore, the emitter has the highest doping level.
The number of flip-flops required in a decade counter is
A)
2
B)
3
C)
4
D)
10
A decade counter counts 10 states (0 to 9). The number of flip-flops required must satisfy 2^n ≥ 10. Since 2^3 = 8 is not enough and 2^4 = 16 is sufficient, 4 flip-flops are required. Hence, option (c) is correct. Options (a), (b), and (d) are incorrect because 2 or 3 flip-flops cannot represent 10 states, while 10 flip-flops are far more than needed.
Out of the following semiconductor power devices, which one is not a current triggered device?
A)
thyristor
B)
GTO
C)
TRIAC
D)
MOSFET
Thyristor, GTO, and TRIAC are current-triggered devices because they require gate current to turn on. A MOSFET is a voltage-controlled device; it is triggered by gate-to-source voltage, not by gate current. Therefore, MOSFET is not a current-triggered device.