← MES Jr. Grade
Past Questions
Describe the flag registers in 8085 microprocessor.
The number of interrupt lines in 8085 microprocessor is
A)
3
B)
4
C)
5
D)
7
The 8085 microprocessor has 5 interrupt lines: TRAP, RST 7.5, RST 6.5, RST 5.5, and INTR. Hence the correct answer is 5. Options 3, 4, and 7 are incorrect because they do not match the standard interrupt structure of the 8085.
The rate at which information can be carried through a communication channel depends on
A)
carrier frequency
B)
bandwidth
C)
transmission loss
D)
transmitted power
The information-carrying capacity of a communication channel is primarily determined by its bandwidth. According to Shannon’s channel capacity concept, a wider bandwidth allows more information to be transmitted per unit time. Carrier frequency does not directly decide capacity, while transmission loss and transmitted power affect signal quality and range, not the basic channel capacity in the same direct way as bandwidth.
In the FM wave described by equation v = 15 sin (4 × 10^8 t + 3 sin 1100 t), the maximum frequency deviation is
A)
175 Hz
B)
525 Hz
C)
58.33 Hz
D)
3 Hz
For an FM wave of the form v = A sin(ωc t + β sin ωm t), the coefficient of sin ωm t is the modulation index β. Here, β = 3 and ωm = 1100 rad/s. The maximum frequency deviation is Δf = β fm, where fm = ωm / (2π) = 1100 / (2π) ≈ 175 Hz. So Δf = 3 × 175 = 525 Hz. Hence, the correct answer is 525 Hz.
What are TE and TM modes? Why is TE called the dominant mode in rectangular waveguide?
The velocity of sound waves in air
A)
is constant at all temperatures
B)
varies directly as temperature
C)
varies inversely as absolute temperature
D)
varies directly as square root of absolute temperature
The speed of sound in air is given by v = \u221a(\u03b3RT/M), so it is proportional to the square root of the absolute temperature (in Kelvin). Hence, as temperature increases, sound velocity increases as \u221aT. Option (a) is wrong because velocity changes with temperature, (b) is wrong because it is not directly proportional to T, and (c) is wrong because it does not vary inversely with temperature.
A waveguide section in a microwave circuit acts as
A)
LP filter
B)
Bandpass filter
C)
HP filter
D)
Bandstop filter
A waveguide has a cutoff frequency: signals below cutoff cannot propagate, while those above cutoff can. This is the behavior of a high-pass filter. Therefore, a waveguide section in a microwave circuit acts as an HP filter. LP filter, bandpass filter, and bandstop filter do not match the basic cutoff nature of a waveguide.
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.
TRIACS can’t be used in AC voltage regulator for a
A)
resistive load
B)
back emf load
C)
inductive load
D)
resistive inductive load
A TRIAC is commonly used in AC voltage regulators with resistive, inductive, and R-L loads. However, it is not suitable for loads having back emf, such as certain motor loads, because the back emf can cause commutation problems and improper turn-off of the TRIAC. Therefore, the correct answer is back emf load.
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.
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.
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.
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.
The most useful modulation technique for high fidelity audio broadcasting on radio in current practice is
A)
amplitude modulation
B)
frequency modulation
C)
pulse amplitude modulation
D)
pulse code modulation
For high-fidelity audio broadcasting, frequency modulation (FM) is preferred because it is much less affected by amplitude noise and interference than amplitude modulation. FM also provides better sound quality and higher immunity to static, which is why it is widely used for radio music and audio broadcasting. Amplitude modulation is more susceptible to noise, while pulse amplitude modulation and pulse code modulation are not used for conventional radio broadcasting in this context.
The number of diodes required in a bridge rectifier circuit is
A)
one
B)
two
C)
three
D)
four
A bridge rectifier uses four diodes arranged in a bridge configuration to convert AC into pulsating DC. During each half-cycle, two diodes conduct and the other two block, ensuring full-wave rectification. Therefore, the number of diodes required is four. Option (a), (b), and (c) are incorrect because a bridge rectifier specifically needs four diodes.
The width of the depletion layer of a junction
A)
Decreases with light doping
B)
Increases with heavy doping
C)
Is independent of applied voltage
D)
Is increased under revered bias
In a p-n junction, the depletion layer width depends on both doping level and applied bias. Under reverse bias, the potential barrier increases and the depletion region widens. Hence option (d) is correct. Option (c) is wrong because depletion width is not independent of applied voltage. Options (a) and (b) are incorrect as stated: light doping actually increases the depletion width, while heavy doping reduces it.
A Z-diode is normally operated in
A)
Forward bias mode
B)
Reverse bias mode
C)
Rectifier mode
D)
Converter mode
A Zener diode is designed to operate in the reverse-bias region, where it maintains an almost constant voltage after breakdown. That is why it is used for voltage regulation. In forward bias, it behaves like an ordinary diode, so option (a) is incorrect. Rectifier mode and converter mode are not the normal operating modes of a Z-diode, so (c) and (d) are incorrect.
In 8085 name the 16 bit registers
A)
Stack pointer
B)
Register B
C)
Register A
D)
PSW
In the 8085 microprocessor, the Stack Pointer (SP) is a 16-bit register because it stores a memory address. Register B and Register A are 8-bit registers, and PSW (Program Status Word) is treated as a 16-bit pair, but in standard single-register form, the clear 16-bit register among the given options is the Stack Pointer. Hence, the correct answer is Stack pointer.
After completing the execution, microprocessor returns to
A)
Halt state
B)
Execute state
C)
Fetch state
D)
Interrupt state
A microprocessor follows the instruction cycle: fetch, decode, execute, and then returns to the fetch state to begin the next instruction. After completing execution of one instruction, it does not halt or go to interrupt state unless an interrupt occurs. Therefore, the correct answer is Fetch state.
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.
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.
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.
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.
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.