← MES Jr. Grade
Past Questions
Crossover distortion behaviour is a characteristic of
A)
Class A
B)
Class B
C)
Class AB
D)
Class C
Crossover distortion occurs in push-pull amplifiers when each transistor in a Class B stage turns off near the zero-crossing point of the input signal. This creates a small dead zone around zero, causing distortion. Class A has no such distortion because the device conducts for the full cycle. Class AB reduces crossover distortion by biasing the transistors slightly on. Class C is used for tuned RF amplification and is not associated with crossover distortion in the same way.
The 8257 chip is a
A)
Programmable interrupt controller
B)
programmable peripheral interface
C)
Programmable DMA controller
D)
programmable interval Timer
The Intel 8257 is a Programmable DMA (Direct Memory Access) controller used to transfer data between memory and I/O devices without continuous CPU involvement. Option (a) refers to 8259, the programmable interrupt controller; option (b) refers to 8255, the programmable peripheral interface; and option (d) refers to 8253/8254, the programmable interval timer.
The open loop gain of an amplifier is 50 but is likely to decrease by 20% due to various factors. If negative feedback with β=0.1 is used the change in gain will be about
A)
20%
B)
10%
C)
3.33%
D)
0.5%
For a feedback amplifier, the closed-loop gain is A_f = A / (1 + Aβ). Here A = 50 and β = 0.1, so the feedback factor is Aβ = 5. Thus the gain reduction sensitivity is 1/(1+Aβ) = 1/6.
If the open-loop gain decreases by 20%, the fractional change in closed-loop gain is approximately:
20% × 1/6 = 3.33%.
So negative feedback greatly stabilizes the gain, reducing the effect of a 20% open-loop variation to about 3.33%.
Hence, the correct answer is (c) 3.33%.
Why others are incorrect:
- 20%: this would be the change without effective feedback stabilization.
- 10%: too large for Aβ = 5.
- 0.5%: too small; would require much larger loop gain.
An OP-Amp has zero gain for common mode inputs. The CMRR is
A)
zero
B)
high
C)
infinite
D)
low
CMRR = differential gain / common-mode gain. If an op-amp has zero gain for common-mode inputs, then common-mode gain = 0. Dividing by zero gives an infinite CMRR. Hence the correct answer is infinite. The other options are incorrect because zero, low, or high do not represent the ideal case when common-mode gain is exactly zero.
The purpose of impedance matching in an amplifier circuit is to achieve
A)
high frequency
B)
reduced distortion
C)
maximum power transfer
D)
none of these
Impedance matching in an amplifier circuit is done so that the load receives the maximum possible power from the source or previous stage. According to the maximum power transfer theorem, this occurs when the load impedance matches the source impedance (or is the complex conjugate in AC circuits). It is not primarily for high frequency operation or reduced distortion.
In Intel 8085, the integer range per word length is
A)
– 128 to 127
B)
– 127 to 128
C)
– 64 to 63
D)
– 63 to 64
Intel 8085 is an 8-bit microprocessor, so one word is 8 bits. For a signed 8-bit integer in two's complement form, the range is from –2^7 to 2^7 – 1, i.e., –128 to 127. Hence option (a) is correct. The other options do not match the standard signed 8-bit range.
Which of the following identifiers is invalid in PASCAL?
A)
Beta
B)
MAX40
C)
2.Nd
D)
A Max
In Pascal, an identifier must begin with a letter and may contain only letters, digits, and sometimes underscores, depending on the compiler. It cannot start with a digit, and it cannot contain a period or space.
- Beta: valid identifier
- MAX40: valid identifier
- 2.Nd: invalid because it starts with a digit and contains a period
- A Max: invalid because it contains a space, but the clearly invalid Pascal identifier among the options is 2.Nd
So the correct answer is 2.Nd.
The polar plot of a transfer function passes through ( - 1, 0 ) point. The gain margin is
A)
Zero
B)
– 1 dB
C)
1 dB
D)
∞
The gain margin is defined as the factor by which the open-loop gain can be increased before the system reaches the verge of instability. If the polar plot passes through the point (-1, 0), the system is already at the critical point of instability, so no further gain increase is possible. Hence the gain margin is zero. The other options are incorrect because a finite positive or negative dB margin would mean the plot has not yet reached (-1, 0), and infinity would mean the plot never reaches the critical point.
If an OP-Amp has unity gain frequency of 1MHz, the cut off frequency at gain 10 will be
A)
100KHz
B)
1MHz
C)
10MHz
D)
90MHz
For a typical op-amp with a constant gain-bandwidth product, the product of closed-loop gain and cutoff frequency remains approximately equal to the unity gain frequency. Here, GBW = 1 MHz. At gain = 10, cutoff frequency = 1 MHz / 10 = 0.1 MHz = 100 kHz. So the correct option is (a). The other options do not satisfy the gain-bandwidth relation.
The open loop gain of an amplifier is 200. If negative feedback with β=0.2 is used, the closed loop gain will be
A)
200
B)
40.12
C)
4.878
D)
2.2
For a negative feedback amplifier, the closed-loop gain is
A_f = A / (1 + Aβ)
Given open-loop gain A = 200 and feedback factor β = 0.2:
Aβ = 200 × 0.2 = 40
So,
A_f = 200 / (1 + 40) = 200 / 41 = 4.878
Hence, the correct answer is 4.878. The other options do not match the standard negative feedback gain formula.
If input frequency is 50Hz, the frequency of output wave in a full wave diode rectifier circuit is
A)
25Hz
B)
50Hz
C)
100Hz
D)
200Hz
In a full-wave rectifier, both the positive and negative half-cycles of the AC input are converted into output pulses. So the output frequency becomes twice the input frequency. For 50 Hz input, output frequency = 2 × 50 = 100 Hz. Hence, option (c) is correct. Option (a) is half-wave related, while (b) is the same as input frequency and (d) is too high.
The force required to initiate motion between two contacting surfaces is called
A)
Coulomb force
B)
viscous force
C)
stiction
D)
none of these
The force needed to start motion between two surfaces in contact is the static friction force, often called stiction. It acts before relative motion begins. Coulomb force refers to friction during motion in an idealized model, and viscous force is resistance due to fluid-like damping, not contact initiation force.
Which amplifier has a voltage again of less than unity?
A)
common base
B)
common collector
C)
common emitter
D)
both CB and CC
A common collector amplifier (emitter follower) has a voltage gain slightly less than 1, i.e., less than unity. In contrast, a common base amplifier has high voltage gain, and a common emitter amplifier also provides voltage gain greater than 1. Therefore, the correct answer is common collector.
Which of the following is difficult to be fabricated in a monolithic IC?
A)
inductors
B)
large capacitors
C)
small capacitors
D)
both (a) and (b)
In monolithic IC fabrication, inductors and large capacitors are difficult to realize on-chip. Inductors require large area and have poor quality factor due to parasitic effects, while large capacitors also consume excessive chip area. Small capacitors can be fabricated more easily. Therefore, the correct answer is both (a) and (b).
In a commercially available good power supply the voltage regulation is about
A)
1%
B)
5%
C)
10%
D)
20%
A good commercially available power supply should have very small variation in output voltage with change in load, i.e., good voltage regulation. Typical good regulated supplies are around 1% regulation. 5%, 10%, and 20% indicate poorer regulation and are not considered good for a commercial power supply.
Which of the following is not treated as hexadecimal constant by 8085 assembler?
A)
234
B)
64QH
C)
A?P0H
D)
all of above
In 8085 assembler, a hexadecimal constant must contain only valid hex digits: 0-9 and A-F, usually ending with H.
- 234 can be treated as a decimal or numeric constant, but in 8085 assembly it is not a valid hexadecimal constant in the strict sense unless written with H suffix as 234H.
- 64QH is invalid because Q is not a hexadecimal digit.
- A?P0H is invalid because ? and P are not hexadecimal digits.
Among the given options, A?P0H is clearly not treated as a hexadecimal constant. Option (d) is incorrect because not all of the above are equally invalid in the same way, and 234 is a valid numeric literal though not a hex constant as written.
Which of the following 8085 instruction does not belong to arithmetic group?
A)
SHLD
B)
SUI
C)
ADC
D)
INR
In 8085, arithmetic instructions include operations like SUI (subtract immediate), ADC (add with carry), and INR (increment). SHLD is not an arithmetic instruction; it is a data transfer instruction used to store the HL pair directly into memory. Therefore, SHLD does not belong to the arithmetic group.
The maximum theoretical efficiency for class A amplifier is
A)
12.5%
B)
25 %
C)
50%
D)
75%
For a class A amplifier, the maximum theoretical efficiency is 25% when using a resistive load. This is because the transistor conducts for the full 360° of the input cycle, causing significant power loss. Option (a) 12.5% is too low, while (c) 50% and (d) 75% are efficiencies associated with other amplifier classes or idealized push-pull arrangements, not class A.
ALE stands for
A)
Address latch enable
B)
accumulator latch enter
C)
address latch enter
D)
accumulator latch enable
ALE in microprocessors stands for Address Latch Enable. It is a control signal used to latch the lower-order address from the multiplexed address/data bus. The other options are incorrect because ALE is not related to accumulator or 'enter'; it specifically refers to address latching.
Which of the following amplifier circuits have highest input impedance?
A)
circuit using BJT
B)
circuit using JFET
C)
circuit using MOSFET
D)
either (a) or (b)
Among the given amplifier circuits, MOSFET-based amplifiers have the highest input impedance because the gate is insulated from the channel by a thin oxide layer, so gate current is almost zero. A JFET also has high input impedance, but it is generally lower than MOSFET. A BJT has the lowest input impedance among these because its base draws input current. Therefore, the correct answer is MOSFET.
A push pull amplifier is a
A)
power amplifier
B)
voltage amplifier
C)
current amplifier
D)
both (a) and (c)
A push-pull amplifier is mainly used as a power amplifier because it delivers higher output power with better efficiency. It also acts as a current amplifier since it can supply a larger load current than the input stage. Therefore, the correct choice is both power amplifier and current amplifier.
When the ac base voltage in a CE amplifier circuit is too high, the ac emitter current is
A)
zero
B)
constant
C)
alternating
D)
distorted
In a common-emitter (CE) amplifier, the emitter current should ideally follow the input signal linearly. If the AC base voltage becomes too high, the transistor is driven beyond its linear operating region, causing non-linear operation. As a result, the AC emitter current becomes distorted. The other options are incorrect because the current does not become zero, constant, or merely alternating in the ideal sense; the key effect of excessive input is distortion.
Transformer coupling is mostly used in
A)
RF amplifier
B)
audio amplifier
C)
both (a) and (b)
D)
None of these
Transformer coupling is mainly used in audio amplifiers because it provides impedance matching between stages and helps transfer maximum power to the load, such as a loudspeaker. In RF amplifiers, transformer coupling is less common; tuned or capacitive coupling is generally preferred for high-frequency operation. Therefore, the correct answer is audio amplifier.
A potential of 7V is applied to a silicon diode in series with a 1KΩ load resistor. If the diode is forward biased, then the current in the circuit is
A)
7mA
B)
6.3mA
C)
0.7mA
D)
zero
For a silicon diode in forward bias, the forward voltage drop is about 0.7 V. So the voltage across the 1 kΩ resistor is 7.0 - 0.7 = 6.3 V. Using Ohm’s law, I = V/R = 6.3/1000 = 6.3 mA. Hence the correct option is (b).
What does the operator ( ) mean in C?
A)
function expression
B)
array expression
C)
structure operator
D)
increment/decrement
In C, the operator ( ) is the function call operator. It is used to call a function, so among the given options the closest and correct answer is 'function expression'. The other options are incorrect: array expression uses [ ], structure operator uses . or ->, and increment/decrement uses ++ or --.