← MES Jr. Grade
Past Questions — 2012
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.
In a CE amplifier circuit the emitter by pass capacitor is removed. The ac output voltage
A)
increases
B)
remains same
C)
decreases
D)
increase or decreases
In a common-emitter (CE) amplifier, the emitter bypass capacitor provides a low-resistance path for AC signals, effectively removing emitter degeneration and increasing gain. If the bypass capacitor is removed, the emitter resistor remains in the AC path, introducing negative feedback (emitter degeneration). This reduces the voltage gain, so the AC output voltage decreases. Hence, option (c) is correct.
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.
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.
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 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.
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.
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.
For dc the current through coupling capacitor in CE amplifier circuit is
A)
very high
B)
high
C)
low
D)
zero
In a CE amplifier, the coupling capacitor is used to pass AC signals and block DC. For DC, a capacitor behaves like an open circuit after it is fully charged, so no steady DC current flows through it. Therefore, the current through the coupling capacitor for DC is zero. Hence, option (d) is correct.
A rectifier circuit has load resistance R and uses a capacitor filter having capacitance C. For low ripple in the output, the value of RC should be
A)
one
B)
low
C)
high
D)
neither low nor high
In a rectifier with a capacitor filter, the capacitor charges near the peak and discharges slowly through the load between peaks. For low ripple, the discharge should be slow, which requires the time constant RC to be much larger than the ripple period. Hence RC should be high. If RC is low, the capacitor discharges quickly and ripple increases.
In an RC phase shift oscillator, the total phase shift of the three RC lead network is
A)
360º
B)
180º
C)
90º
D)
0º
In an RC phase shift oscillator, each RC lead network contributes a phase shift of about 60º. With three such sections, the total phase shift is 3 × 60º = 180º. The amplifier provides the remaining 180º, making the total loop phase shift 360º (or 0º), which satisfies the Barkhausen criterion. Hence, the total phase shift of the three RC lead network is 180º.
In every practical oscillator the loop gain is slightly more than unity and amplitude of oscillations is limited by
A)
magnitude of loop gain
B)
onset of non linearity
C)
magnitude of gain
D)
feedback factor
In a practical oscillator, the loop gain is made slightly greater than 1 so that oscillations can start. As the amplitude grows, the active device enters the nonlinear region, which reduces the effective gain and stabilizes the output amplitude. Hence, the amplitude is limited by the onset of non-linearity. The other options are not the main limiting factor: loop gain and feedback factor help determine whether oscillations start, but amplitude stabilization occurs due to nonlinearity.
The self bias provides
A)
stable Q point
B)
large voltage gain
C)
high input impedance
D)
high base current
Self-bias in a transistor amplifier uses negative feedback to keep the operating point (Q-point) stable against changes in temperature, transistor parameters, and supply variations. It does not primarily increase voltage gain, input impedance, or base current. Hence, the correct answer is stable Q point.
8255A is a
A)
PPI
B)
I/O device
C)
memory
D)
none of above
8255A is the Intel 8255A Programmable Peripheral Interface (PPI) chip. It is used to interface peripheral devices with microprocessors through programmable input/output ports. It is not a memory device, and while it functions as an I/O interface, its specific standard classification is PPI.
A CE amplifier has re=6Ω, β=100. The input impedance is
A)
6Ω
B)
98Ω
C)
100Ω
D)
600Ω
For a common-emitter (CE) amplifier, the input impedance seen at the base is approximately r_in = β × re. Given re = 6Ω and β = 100, the input impedance is 100 × 6 = 600Ω. Hence, the correct option is (d). Options (a), (b), and (c) are too small and do not match the CE input impedance relation.
If the mid band gain of an amplifier is 40dB, the gain at half power frequency is
A)
37dB
B)
30dB
C)
20dB
D)
13dB
At the half-power frequency, the output power drops to half of the mid-band value. A half-power point corresponds to a decrease of 3 dB in gain. So, if the mid-band gain is 40 dB, the gain at half-power frequency is 40 - 3 = 37 dB. Hence, option (a) is correct.
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.
In a nickel-cadmium-alkali cell the electrolyte is
A)
sulphur acid
B)
potassium hydroxide
C)
zinc chloride
D)
ammonium chloride
A nickel-cadmium (Ni-Cd) cell is an alkaline cell, and its electrolyte is potassium hydroxide (KOH). Sulphuric acid is used in lead-acid cells, while zinc chloride and ammonium chloride are used in dry cells.
In an unbiased P-N junction, thickness of depletion layer is of the order of
A)
0.005µm
B)
0.5 µm
C)
5 µm
D)
1nm
In an unbiased P-N junction, the depletion region is typically of the order of a fraction of a micrometre. A common approximate value is about 0.5 µm. Option (a) 0.005 µm and (d) 1 nm are too small, while (c) 5 µm is generally too large for an unbiased junction.
The temperature at which a material becomes a glassy solid is called
A)
melting temperature
B)
recrystallization temperature
C)
glass transition temperature
D)
freezing temperature
The temperature at which an amorphous material changes from a rubbery or viscous state into a hard, glassy solid is called the glass transition temperature (Tg). This is different from melting temperature, which applies to crystalline solids. Recrystallization temperature is related to crystal formation, and freezing temperature is the liquid-to-solid change point for ordinary substances, not the specific glassy transition.
Which of the following is not a piezo-electric material?
A)
Rochell salt
B)
quartz
C)
lithium sulphate
D)
sodium-bicarbonate
Rochelle salt, quartz, and lithium sulphate are well-known piezo-electric materials. Sodium bicarbonate is not used as a piezo-electric material. Therefore, the correct answer is sodium-bicarbonate.
the signal to noise ratio in telemetry should be
A)
5 dB
B)
10 dB
C)
25 dB
D)
60 dB
In telemetry systems, the signal-to-noise ratio should be very high to ensure reliable transmission and accurate reception of measured data. Among the given options, 60 dB is the most appropriate and standard desirable value. Lower values like 5 dB, 10 dB, or even 25 dB indicate comparatively poor noise immunity and are not suitable for telemetry.
A digital voltmeter has a readout range from 0 to 999 counts. If the full scale reading is 9.999V, the resolution is
A)
1V
B)
10mV
C)
1mV
D)
0.001mV
A digital voltmeter with a readout of 0 to 999 counts and a full-scale reading of 9.999 V has 1000 possible display steps. So the least significant digit corresponds to 9.999 V / 999 ≈ 0.01 V? But in standard DVM notation, 9.999 V means the smallest increment is 0.001 V = 1 mV. Hence the resolution is 1 mV. The other options are too coarse or too fine.
The unit of electrical conductivity is
A)
mho/meter
B)
mho/m2
C)
ohm/m
D)
ohm/m2
Electrical conductivity is the reciprocal of resistivity. Since resistivity has unit ohm-meter (Ω·m), conductivity has unit 1/(Ω·m), which is commonly written as mho per meter (or siemens per meter). Therefore, option (a) is correct. Options (c) and (d) are units related to resistance/resistivity, not conductivity.
The term ‘Poisson’s ratio’ is connected with
A)
strain gauge
B)
LVDT
C)
bourden tube
D)
thermistor
Poisson’s ratio is directly used in strain gauge measurements because a strain gauge senses both longitudinal and lateral strain, and the ratio of lateral strain to longitudinal strain is Poisson’s ratio. This is important in strain gauge factor calculations. LVDT measures displacement, Bourdon tube measures pressure, and thermistor measures temperature, so they are not connected with Poisson’s ratio.