← MES Jr. Grade
Past Questions
In FM, when frequency deviation is doubled,
A)
modulation is doubled
B)
modulation is halved
C)
carrier swing is halved
D)
modulation index is decreased
In frequency modulation (FM), the modulation index is directly proportional to the frequency deviation. If the frequency deviation is doubled, the modulation index also doubles. Hence, the correct option is (a) modulation is doubled. The other options are incorrect because halving the modulation or carrier swing would be the opposite effect, and the modulation index does not decrease when deviation increases.
An ideal amplifier has
A)
noise figure of less than 1dB
B)
noise factor of unity
C)
output signal to noise ratio (S/N) more than input S/N
D)
noise figure of more than 0dB
An ideal amplifier adds no noise to the signal, so its noise factor is 1 (unity). Since noise figure = 10 log10(noise factor), the noise figure of an ideal amplifier is 0 dB. Therefore, option (b) is correct. Option (a) is incorrect because an ideal amplifier has 0 dB noise figure, not less than 1 dB specifically. Option (c) is incorrect because an ideal amplifier does not improve S/N ratio; it preserves it. Option (d) is incorrect because noise figure greater than 0 dB means the amplifier adds noise.
If the carrier of a 100 percent modulated AM wave is suppressed, the percentage power saving will be
A)
50
B)
33.33
C)
100
D)
66.66
In standard AM, total power is P_t = P_c(1 + m^2/2), where m is the modulation index. For 100% modulation, m = 1, so P_t = 1.5 P_c. If the carrier is suppressed, only the sideband power remains: P_s = P_c(m^2/2) = 0.5 P_c. Hence power saved = (1.5P_c - 0.5P_c) / 1.5P_c × 100 = 1/1.5 × 100 = 66.66%. So the correct option is (d). Other options do not match the standard AM power relations.
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 fundamentally built around two main parts: the Arithmetic Logic Unit (ALU), which performs arithmetic and logical operations, and the Control Unit, which directs and coordinates all operations. Memory and I/O devices are not basic internal elements of the microprocessor; they are external components interfaced with it. Therefore, the correct answer is ALU and control unit.
A microprocessor with a 12-bit address bus will be able to access
A)
1 kilobyte of memory
B)
4 kilobytes of memory
C)
8 kilobytes of memory
D)
0.4 kilobytes of memory
A 12-bit address bus can generate 2^12 = 4096 unique addresses. If each address refers to 1 byte of memory, the total accessible memory is 4096 bytes = 4 KB. However, since the options include 4 KB as option (b), that is the correct choice. The other options are incorrect because 1 KB = 1024 bytes, 8 KB would require 13 address bits, and 0.4 KB is far too small.
Ripple frequency of the output waveform of a bridge rectifier when fed with a 50Hz sine wave is
A)
100Hz
B)
25Hz
C)
50Hz
D)
200Hz
In a bridge rectifier, both half-cycles of the AC input are converted into pulsating DC. Therefore, the ripple frequency is twice the input frequency. For a 50 Hz supply, ripple frequency = 2 × 50 = 100 Hz. Hence, option (a) is correct. Option (b) 25 Hz is too low, option (c) 50 Hz is the input frequency, and option (d) 200 Hz would correspond to a 100 Hz input.
Silicon is invariably used in the manufacture of photodiodes because
A)
more electron-hole pairs are generated in it
B)
its thermally-generated minority current is extremely small
C)
it is more rugged than Ge
D)
it needs less reverse bias
Silicon is preferred for photodiodes because it has a much lower intrinsic carrier concentration than germanium, so the thermally generated minority current is very small. This reduces dark current and improves sensitivity and stability. Option (a) is incorrect because the key advantage is not generating more electron-hole pairs, but lower unwanted thermal generation. Option (c) may be true in a general sense, but it is not the main electrical reason for photodiode use. Option (d) is incorrect because the required reverse bias depends on device design, not the material choice in this way.
Which of the following actions detect locations, and remove mistakes from a program routine?
A)
Erase
B)
Debug
C)
Diagnose
D)
Emulate
Debugging is the process of detecting the location of errors (bugs) in a program and removing them. 'Erase' means delete, 'Diagnose' means identify a problem but not specifically fix program errors, and 'Emulate' means imitate the behavior of another system or device.
The primary function of a clamper circuit is to
A)
suppress variations in signal voltage
B)
raise positive half-cycle of the signal
C)
lower negative half-cycle of the signal
D)
introduce a D.C. level into an A.C. signal
A clamper circuit shifts the entire waveform up or down by adding a DC component, without changing the shape of the signal. Its main purpose is to introduce a D.C. level into an A.C. signal. Option (a) refers more to filtering/regulation, while (b) and (c) describe only partial effects of shifting, not the primary function.
In 8085 microprocessor system, the direct addressing instruction is
A)
MOVA, B
B)
MOVB, OAH
C)
MOVC, M
D)
STA addr
In 8085, direct addressing means the instruction contains the 16-bit memory address of the operand explicitly in the instruction.
- STA addr: stores the accumulator directly into the memory location specified by addr, so it uses direct addressing.
- MOV A, B: register addressing, because both operands are registers.
- MOV B, 0AH: this is not a valid 8085 instruction as written; if intended as MVI B, 0AH, that would be immediate addressing.
- MOV C, M: register-indirect addressing, because M refers to the memory location pointed to by HL.
Therefore, the correct answer is STA addr.
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, typically about 530 kHz to 1700 kHz internationally, and in many exam contexts is given approximately as 500 kHz to 1500 kHz. Option (b) matches this band. Option (a) is too low, option (c) is a much wider range covering HF, and option (d) is VHF, not AM broadcast.
If the drain to source resistance of FET is controlled by the bias voltage VGS, FET is also referred to as a
A)
voltage variable transistor
B)
current variable resistor
C)
voltage variable resistor
D)
current variable transistor
In a FET, the drain-to-source resistance is controlled by the gate-to-source voltage VGS. Since the resistance changes with an applied voltage, the FET is called a voltage variable resistor. Option (a) is incorrect because the device is not usually termed a transistor in this context; option (b) is wrong because the controlling quantity is not current; option (d) is incorrect because the FET is not controlled by current.
A push-pull amplifier suppresses
A)
only the second harmonic component
B)
only the odd harmonic components
C)
only the even harmonic components
D)
both odd and even harmonic components
In a push-pull amplifier, the two transistors/valves conduct on alternate half-cycles and their outputs are combined in such a way that the even-order harmonics cancel out. This is because the even harmonics are in phase opposition in the two halves, while the odd harmonics add. Therefore, a push-pull amplifier suppresses only the even harmonic components. Option (a) is too specific, and (b) and (d) are incorrect.
For an amplifier, the coupling method which gives the highest gain is
A)
capacitive coupling
B)
resistance coupling
C)
impedance coupling
D)
transformer coupling
Transformer coupling gives the highest gain among the given coupling methods because it can provide impedance matching between stages and transfer maximum power to the load. Capacitive and resistance coupling are common for voltage amplification, but they do not provide as high a gain as transformer coupling. Impedance coupling is also not generally superior to transformer coupling in terms of gain.
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. During each half-cycle of AC input, two diodes conduct and two are reverse-biased, but the circuit as a whole requires 4 diodes. Hence, the correct answer is four.
Which stage of a D.C. power supply uses a Zener as the main component?
A)
rectifier
B)
voltage divider
C)
regulator
D)
filter
A Zener diode is commonly used in the regulation stage of a D.C. power supply because it maintains an almost constant output voltage despite changes in input voltage or load current. A rectifier converts AC to DC, a filter smooths the pulsations, and a voltage divider only splits voltage—it does not provide regulation.
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. Therefore, the output becomes 0 only when both inputs are 0. If either input is 1, the output is 1, so options (b), (c), and (d) are incorrect.
An SCR has
A)
one terminal
B)
two terminals
C)
three terminals
D)
four terminals
An SCR (Silicon Controlled Rectifier) is a thyristor device with three terminals: anode, cathode, and gate. The gate terminal is used to trigger the device into conduction. Hence, the correct answer is three terminals. The other options are incorrect because an SCR is not a one-, two-, or four-terminal device.
Out of the following devices, the fastest switching device is
A)
JEFT
B)
BJT
C)
MOSFET
D)
triode
MOSFETs are the fastest switching devices among the given options because they are majority-carrier devices and do not suffer from charge storage delay. A JFET is also a field-effect device, but MOSFETs are generally preferred for very fast switching in digital and power applications. A BJT is slower due to minority-carrier storage effects, and a triode vacuum tube is much slower and obsolete for such applications.
Which of the following systems is preferred for chopper drives?
A)
Constant frequency system
B)
Variable frequency system
C)
constant voltage system
D)
none of these
Chopper drives are generally preferred with a constant frequency system because it gives better control, simpler design, and easier filtering of ripple. In chopper control, the output voltage is varied by changing the duty ratio while keeping the switching frequency fixed. Variable frequency systems are more common in some other drive/control schemes, but for chopper drives constant frequency operation is preferred. Hence, option (a) is correct.
The most commonly used filters in SSB generation are
A)
RC
B)
mechanical
C)
LC
D)
low pass
In SSB generation, the filter method commonly uses band-pass or crystal/LC filters to select one sideband and suppress the other. Among the given options, LC is the most commonly used practical filter type. RC filters are generally used at lower frequencies and mechanical filters are not the usual standard answer here. ‘Low pass’ is not the typical answer for SSB generation filters.
A modulator is a system to
A)
separate two frequencies
B)
impress the information on to a radio frequency carrier
C)
extract information from the carrier
D)
amplify the audio frequency signal
A modulator is used in communication systems to place the message or information signal onto a high-frequency carrier wave for transmission. This process is called modulation. Option (c) describes a demodulator, which extracts information from the carrier. Option (a) is unrelated, and option (d) refers to amplification, not modulation.
In a microprocessor, the address of the next instruction to be executed is stored in
A)
stack pointer
B)
address latch
C)
program counter
D)
general purpose register
The Program Counter (PC) stores the address of the next instruction to be executed in a microprocessor. After each instruction fetch, the PC is automatically updated to point to the following instruction. The stack pointer stores the top of the stack, the address latch temporarily holds address information during bus operations, and general-purpose registers are used for data manipulation, not for tracking the next instruction.
An SCR is operated
A)
only in reverse-biased condition
B)
only in forward biased condition
C)
both forward and reverse biased conditions
D)
none of these
An SCR (Silicon Controlled Rectifier) is a unidirectional controlled device. It is normally operated in the forward-biased condition, where it can be triggered into conduction by a gate pulse. In reverse bias, it blocks current and is not used for normal operation. Hence, the correct option is (b). Option (a) is wrong because reverse bias is for blocking, not operation. Option (c) is wrong because an SCR does not conduct in both directions like a bidirectional device.
An SCR is a
A)
two-layer two junction device
B)
three-layer two junction device
C)
four-layer three junction device
D)
four-layer four junction device
An SCR (Silicon Controlled Rectifier) is a PNPN device, meaning it has four layers and three junctions. Hence, it is correctly described as a four-layer three junction device. Option (a) and (b) have too few layers/junctions, and option (d) is incorrect because a four-layer device has only three junctions.