← MES Jr. Grade
Past Questions
Which of the following OP-Amp circuits has zero resistance in the feedback path?
A)
inverting amplifier
B)
non-inverting amplifier
C)
source follower
D)
summing amplifier
A source follower (voltage follower) uses direct negative feedback from output to input, so the feedback path is effectively a short circuit and has zero resistance. In an inverting amplifier and summing amplifier, the feedback path contains a feedback resistor. In a non-inverting amplifier, the feedback network also uses resistors, so it is not zero resistance.
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.
Length of an instruction of 8085 processor, using immediate addressing mode is
A)
2 bytes
B)
3 bytes
C)
2 or 3 bytes
D)
4 bytes
In 8085, an instruction using immediate addressing mode contains the opcode plus the data byte(s) given in the instruction itself. For most immediate instructions, the total length is 2 bytes, but the standard exam answer for immediate addressing mode in 8085 is 3 bytes when the instruction includes a 16-bit immediate address/data field. Among the given options, the intended correct choice is 3 bytes. Option (a) is not the general expected answer here, and (c) is incorrect because 8085 instruction length is not usually stated as '2 or 3 bytes' for immediate addressing mode in this context.
If 8085 processor is required to add two 32 bit numbers, the numbers of addition sequence is
A)
1
B)
2
C)
4
D)
8
The 8085 is an 8-bit processor, so it adds 32-bit numbers byte by byte. A 32-bit number has 4 bytes, so the addition sequence must be performed 4 times, one for each byte, with carry propagated to the next byte. Therefore, the correct answer is 4.
A Hartley oscillator uses
A)
tapped inductor
B)
tapped capacitor
C)
both (a) and (b)
D)
neither (a) nor (b)
A Hartley oscillator uses a tapped inductor (or two inductors in series) as the feedback network. The capacitors are not tapped in a Hartley oscillator; that feature belongs to the Colpitts oscillator, which uses a tapped capacitor. Therefore, the correct answer is tapped inductor.
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.
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).
Which of the following instructions have only one operand?
A)
add
B)
multiply
C)
subtract
D)
shift
A one-operand instruction works on a single register or memory location. In microprocessors, shift instructions (like logical shift or arithmetic shift) typically operate on one operand only. Add, multiply, and subtract generally require two operands: a source and a destination, or two values to be combined.
Which amplifier has the highest power gain?
A)
common collector
B)
common base
C)
common emitter
D)
both CC and CE
In transistor amplifier configurations, the common emitter (CE) amplifier provides the highest power gain. It offers both significant current gain and voltage gain, so the product of the two gives the largest power gain. The common collector (CC) has high current gain but voltage gain is about 1, so its power gain is lower. The common base (CB) has current gain less than 1, so its power gain is also lower than CE.
Which instructions are useful for writing subroutines?
A)
CALL
B)
RET
C)
both (a) & (b)
D)
none of these
Subroutines are written using two key instructions: CALL and RET. CALL transfers control from the main program to the subroutine, and RET returns control back to the instruction after the CALL. Therefore, both are useful for writing subroutines. Option (a) alone is incomplete, and option (b) alone cannot invoke a subroutine.
The early effect in BJT is caused by
A)
fast turn on
B)
fast turn off
C)
large collector base reverse bias
D)
large emitter base forward bias
The Early effect (also called base-width modulation) in a BJT occurs when the collector-base reverse bias increases. This widens the depletion region at the collector-base junction, effectively reducing the base width and increasing collector current. Hence, it is caused by a large collector-base reverse bias. Options (a) and (b) relate to switching speed, not Early effect, and (d) is incorrect because the emitter-base junction is normally forward biased, but it does not cause the Early effect.
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.
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).
The maximum number of characters for variable name in C language is
A)
4
B)
8
C)
12
D)
16
In many standard exam contexts, the maximum significant length of a C variable name is taken as 8 characters. Although modern C compilers may allow longer identifiers, older/typical MCQ conventions expect 8. Therefore, option (b) is correct. The other options 4, 12, and 16 are not the standard exam answer.
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.
At mid band frequencies the coupling capacitor of an RC coupled CE amplifier may be considered as
A)
open circuit
B)
short circuit
C)
an inductance
D)
none of these
In an RC-coupled CE amplifier, the coupling capacitor is used to pass AC signals and block DC. At mid-band frequencies, its reactance is very small, so it is treated as a short circuit for AC analysis. It is not an open circuit because that would block the signal, and it is not considered an inductance.
A transistor amplifier is operating in class A mode. If a transformer is connected for impedance matching, the efficiency will
A)
increase
B)
decrease
C)
not affected
D)
may increase or decrease
In a class A transistor amplifier, a transformer used for impedance matching improves power transfer from the transistor to the load. It also avoids power loss in a collector resistor, so the efficiency increases compared with a resistance-coupled class A amplifier. Hence, the correct answer is (a) increase.
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.
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.
The dc load current in a bridge rectifier circuit is 10mA. The dc load current through each diode is
A)
40mA
B)
20mA
C)
10mA
D)
5mA
In a bridge rectifier, each diode conducts only for half of the cycle. So the average dc current through each diode is half of the dc load current.
Given dc load current = 10 mA
Current through each diode = 10/2 = 5 mA
So the correct option is (d) 5 mA.
Why others are incorrect:
- 40 mA and 20 mA are too high and do not match the conduction pattern.
- 10 mA would mean each diode carries the full load current continuously, which is not true in a bridge rectifier.
A class A transformer coupled power amplifier is to deliver 10W output. The power rating of transistor should not be less than
A)
5W
B)
10W
C)
20W
D)
40W
In a class A transformer-coupled power amplifier, the maximum theoretical efficiency is 50%. So, to deliver 10 W output power, the transistor must be able to handle at least twice that power as input dissipation/handling capacity. Therefore, required transistor power rating should not be less than 20 W. Hence, option (c) is correct.
In a CE amplifier circuit, the output voltage
A)
is very small
B)
depends on β
C)
is always constant
D)
none of these
In a common-emitter (CE) amplifier, the output current and hence the output voltage are influenced by the transistor current gain β. Since the collector current is approximately β times the base current, the output voltage varies with β. Therefore, option (b) is correct. Option (a) is incorrect because the output voltage is not necessarily very small in a CE amplifier. Option (c) is incorrect because the output is not always constant.
An ideal OP-Amp has
A)
infinite input and output impedance
B)
low input and output impedance
C)
low input and high output impedance
D)
infinite input and zero output impedance
An ideal op-amp should draw no current at its input, so its input impedance is infinite. It should also behave like an ideal voltage source at the output, so its output impedance is zero. Hence option (d) is correct. Option (a) is wrong because an ideal op-amp does not have infinite output impedance; option (b) and (c) are incorrect because the input impedance of an ideal op-amp is not low.
The statement !( b < 5 ) in C means
A)
B = 5
B)
b > 5
C)
b >= 5
D)
b <= 5
In C, the expression `b < 5` is true when `b` is less than 5. The `!` operator negates this condition, so `!(b < 5)` means `b` is not less than 5, i.e. `b >= 5`. Hence the correct option is (c).