← MES Jr. Grade
Past Questions
Instruction CALL of a 8085 microprocessor has
A)
1 byte
B)
2 bytes
C)
4 bytes
D)
3 bytes
In the 8085 microprocessor, the CALL instruction is a 3-byte instruction. It consists of: 1 byte for the opcode and 2 bytes for the 16-bit address of the subroutine to be called. Therefore, the correct answer is 3 bytes. The other options are incorrect because CALL cannot be represented in only 1 or 2 bytes, and 4 bytes is not the standard length for this instruction.
The output of a 2-input OR gate is zero only when
A)
both inputs are 0
B)
either input is 0
C)
both inputs are 1
D)
either input is 1
For a 2-input OR gate, the output is 1 if at least one input is 1. It becomes 0 only in the single case when both inputs are 0. Hence, option (a) is correct. Options (b) and (d) are incorrect because if either input is 1, the OR output is 1. Option (c) is the case where the output is definitely 1, not 0.
Instruction RET (Return) of a 8085 microprocessor
A)
Stack Pointer and Program counter
B)
Stack Pointer only
C)
Program counter only
D)
Set Interrupt Mask and Acc
In the 8085, the RET instruction returns from a subroutine by restoring the saved address from the stack into the Program Counter (PC). This operation uses the Stack Pointer (SP) to access the top of the stack and then updates the PC with the return address. Hence, both the Stack Pointer and Program Counter are involved. Option (b) is incomplete, (c) ignores the stack access, and (d) is unrelated.
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.
Eight memory chips of 32×4 bit size have their address buses connected together. What is the size of this memory system?
A)
512×2 bits
B)
256×4 bits
C)
64×16 bits
D)
32×32 bits
Each chip is 32×4 bits, meaning it has 32 memory locations and each location stores 4 bits. If 8 such chips have their address buses connected together, they all respond to the same 32 addresses. Since their data buses are combined, the data width adds up: 8 × 4 = 32 bits. So the overall memory organization is 32 locations of 32 bits each, i.e. 32×32 bits. The other options do not match the combined word size.
The depletion region in an open circuited P-N junction diode contains
A)
Electrons
B)
Holes
C)
Uncovered immobile impurity ions
D)
Neutralised impurity atoms
In an open-circuited P-N junction, electrons and holes near the junction diffuse and recombine. This leaves behind fixed donor ions on the N-side and fixed acceptor ions on the P-side. These are immobile impurity ions, which form the depletion region. Therefore, the correct option is (c). Options (a) and (b) are incorrect because free electrons and holes are depleted from this region, and (d) is incorrect because the atoms are not neutral there; the ions are uncovered and charged.
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 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, also called an emitter follower, is known for high input impedance, low output impedance, and high current gain. Its voltage gain is approximately unity (slightly less than 1), not high. Therefore, 'High voltage gain' is the incorrect specification.
Which of the following has the longest wavelength?
A)
HF
B)
VHF
C)
UHF
D)
SHF
In the radio-frequency spectrum, wavelength is inversely proportional to frequency. Among the given bands, HF (High Frequency) has the lowest frequency range, so it has the longest wavelength. VHF, UHF, and SHF have progressively higher frequencies and therefore shorter wavelengths.
In microprocessor architecture, flag indicates
A)
the number of the microprocessor
B)
the name of the manufacturer
C)
the internal status of the CPU
D)
the bit size of the microprocessor
In a microprocessor, the flag register contains status flags such as carry, zero, sign, overflow, etc. These flags represent the internal status of the CPU after arithmetic or logical operations. Therefore, the correct answer is the internal status of the CPU. The other options are incorrect because flags do not indicate the processor number, manufacturer name, or bit size.
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. Therefore, the carrier parameter changed in AM is amplitude. The other options correspond to other modulation types: frequency in FM, phase in PM, and pulse width in PWM.
An EX-OR gate produces an output only when its two inputs are
A)
Same
B)
Different
C)
High
D)
low
An EX-OR (XOR) gate gives output 1 only when its two inputs are different, i.e., one is high and the other is low. If both inputs are the same, the output is 0. So option (b) is correct. Options (a), (c), and (d) are incorrect because XOR does not produce output for identical inputs or for just any high/low input individually.
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.
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.
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.
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 assembly language source code into machine code. The machine-code output produced by the assembler is called an object program (or object code).
Why others are incorrect:
- (b) Source program: this is the original assembly language input, not the output.
- (c) Macroinstruction: this is a higher-level assembly directive/instruction, not the machine-code output.
- (d) Symbolic instruction: this refers to assembly language mnemonics, not the assembled machine code.
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.
The basic elements of a microprocessor are
A)
ALU and memory
B)
ALU and control unit
C)
ALU, memory and I/O devices
D)
ALU, control unit and memory
A microprocessor is essentially a CPU on a single chip. Its fundamental functional blocks are the Arithmetic Logic Unit (ALU), which performs arithmetic and logic operations, and the control unit, which directs and coordinates operations. Memory and I/O devices are not basic internal elements of the microprocessor itself; they are external components interfaced with it. Hence, option (b) is correct.
A zener diode
A)
Has a high forward voltage rating
B)
Has a sharp breakdown at low reverse voltage
C)
Is useful as an amplifier
D)
Has a negative resistance
A Zener diode is designed to operate in reverse bias at a specific, low breakdown voltage. It has a very sharp breakdown characteristic, so the voltage remains nearly constant over a wide current range after breakdown. Option (a) is wrong because the key feature is reverse breakdown, not high forward voltage rating. Option (c) is wrong because a Zener diode is not used as an amplifier. Option (d) is not the best answer here; while the breakdown region shows negative resistance behavior in some contexts, the standard defining feature of a Zener diode is its sharp breakdown at low reverse voltage.
In a self controlled synchronous motor fed from a variable frequency inverter,
A)
the rotor poles invariably have damper windings
B)
there are stability problems
C)
the speed of the rotor decides stator frequency
D)
the frequency of the stator decides the rotor speed
In a self-controlled synchronous motor, the inverter frequency is made to follow the rotor position/speed so that the stator field remains synchronized with the rotor. Hence, the rotor speed determines the stator supply frequency. Option (d) describes the normal grid-fed synchronous motor concept in the opposite direction. Option (a) is not invariably true, and option (b) is not the defining feature here.
A broadcast AM radio transmitter radiates 125 kW when the modulation percentage is 70. How much of this is carrier power?
A)
≈25 kW
B)
50 kW
C)
75 kW
D)
100 kW
For standard AM, total transmitted power is P_t = P_c(1 + m^2/2), where P_c is carrier power and m is modulation index. Given P_t = 125 kW and m = 0.7, we get P_t = P_c(1 + 0.49/2) = P_c(1.245). So P_c = 125/1.245 ≈ 100.4 kW. However, the options suggest the intended simplified relation may be based on power in sidebands or a textbook approximation. For the usual AM power formula, the carrier power is about 100 kW, which matches option (d), not (c).
After firing an SCR, the gate pulse is removed. The current in the SCR will
A)
remain the same
B)
immediately fall to zero
C)
rise up
D)
rise a little and then fall to zero
An SCR, once triggered, latches into conduction. After firing, the gate pulse can be removed and the SCR will continue to conduct as long as the anode current stays above the holding current. Therefore, the current does not immediately fall to zero just because the gate signal is removed. Options (b), (c), and (d) are incorrect because gate removal does not control the conducting current directly after turn-on.
Out of the following devices, the fastest switching device is
A)
JFET
B)
BJT
C)
MOSFET
D)
triode
MOSFET is the fastest switching device among the given options because it is a majority-carrier device and has no charge-storage delay. JFET is also a field-effect device but is generally slower than MOSFET in switching applications. BJT is slower because it is a minority-carrier device and suffers from storage time during turn-off. A triode vacuum tube is much slower and obsolete for modern high-speed switching compared to semiconductor devices. Hence, the correct answer is MOSFET.
A power chopper converts
A)
a.c. to .d.c
B)
d.c. to d.c.
C)
d.c. to a.c.
D)
a.c. to a.c.
A power chopper is a static power electronic device used to control and convert a fixed d.c. input into a variable d.c. output. Hence, it performs d.c. to d.c. conversion.
Why others are wrong:
- (a) a.c. to d.c. is done by a rectifier.
- (c) d.c. to a.c. is done by an inverter.
- (d) a.c. to a.c. is done by an ac voltage controller or cycloconverter, depending on frequency conversion.
A modern power semiconductor device that combines the characteristics of BJT and MOSFET is
A)
GTO
B)
FCT
C)
IGBT
D)
MCT
The IGBT (Insulated Gate Bipolar Transistor) combines the input characteristics of a MOSFET with the output/conduction characteristics of a BJT. It has high input impedance like a MOSFET and low on-state voltage drop like a bipolar device.
Why others are incorrect:
- GTO: A thyristor that can be turned off by gate signal, but it does not combine MOSFET and BJT features.
- FCT: Field Controlled Thyristor, not the standard device described here.
- MCT: MOS-Controlled Thyristor, also a gate-controlled thyristor, but the device specifically known for combining MOSFET and BJT characteristics is IGBT.