← MES Jr. Grade
Past Questions
The main reason why electrons can tunnel through a P-N junction is that
A)
they have high energy
B)
barrier potential is very low
C)
depletion layer is extremely thin
D)
impurity level is low
In a P-N junction, tunneling occurs when the depletion region becomes extremely thin, so electrons can pass through the potential barrier by quantum tunneling. This is the principle behind tunnel diodes. The other options are incorrect because tunneling is not mainly due to high electron energy, low barrier potential alone, or low impurity level.
The clipping level is primarily determined by
A)
the shape of the input waveform
B)
battery voltage
C)
value of the resistor
D)
knee voltage of the diode
In a diode clipper circuit, clipping starts when the input exceeds the diode’s forward conduction threshold. Therefore, the clipping level is mainly set by the diode’s knee voltage (and any biasing, if present). The input waveform shape does not determine the clipping level, and the resistor mainly limits current rather than fixing the clip point. Battery voltage can shift the clipping level in biased clippers, but in the basic case the diode knee voltage is the primary factor.
In microprocessors, flag is a character for
A)
identification of a word
B)
occurrence of some condition
C)
marking a tagging
D)
all of these
In a microprocessor, a flag is a status bit used to indicate the occurrence of a particular condition, such as zero result, carry, sign, overflow, etc. Hence, the correct meaning is 'occurrence of some condition'. Option (a) is incorrect because a flag does not identify a word, and option (c) is too vague. Therefore, (d) cannot be correct.
The antenna employed in television receivers is a
A)
half-wave dipole
B)
yagi antenna
C)
rhombic antenna
D)
horn antenna
Television receivers commonly use a Yagi antenna because it is a directional antenna with high gain and good reception of VHF/UHF TV signals. A half-wave dipole is a basic antenna element, but not the typical TV receiving antenna by itself. Rhombic antennas are large directional antennas used mainly for long-distance HF communication, and horn antennas are generally used at microwave frequencies, not for ordinary TV reception.
The amplifier circuit suitable for impedance matching is
A)
common base
B)
common collector
C)
common emitter
D)
all of these
A common collector amplifier (emitter follower) is best suited for impedance matching because it has very high input impedance and very low output impedance. This allows it to transfer voltage effectively from a high-impedance source to a low-impedance load. A common emitter amplifier gives high voltage gain but is not primarily used for impedance matching, and a common base amplifier has low input impedance, so it is also not the usual choice for matching.
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.
In a single-stage CB amplifier, a smaller load resistance R L will produce
A)
high current gain
B)
high voltage gain
C)
better frequency response
D)
higher power gain
In a common-base (CB) amplifier, the current gain is less than 1, while the voltage gain is high. If the load resistance RL is made smaller, the output RC time constant decreases, which improves the high-frequency response. Hence a smaller load resistance generally gives better frequency response. It does not increase current gain, and power gain is not the main effect here.
In AM system, full information can be conveyed by transmitting only
A)
the carrier
B)
the upper sideband
C)
the lower sideband
D)
any one sideband
In amplitude modulation (AM), the information is contained in the sidebands, not in the carrier itself. Since the upper sideband and lower sideband are mirror images and each contains the complete message information, transmitting only one sideband is sufficient to convey full information. The carrier alone carries no information, and a single specified sideband (upper or lower) can be used. Therefore, the correct answer is 'any one sideband'.
Number of operators required to build a 5-bit Analog to Digital converter is
A)
5
B)
11
C)
21
D)
31
For an n-bit flash ADC, the number of comparators required is 2^n - 1. Here n = 5, so required comparators = 2^5 - 1 = 32 - 1 = 31. Hence the correct answer is 31. The other options do not match the standard flash ADC comparator count.
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.
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.
The input resistance of a MOSFET is
A)
very high as compared to that of a bipolar transistor
B)
low as compared to that of a bipolar transistor
C)
of the same order as of a bi-polar transistor
D)
none of the above
A MOSFET has an insulated gate, so the gate current is almost zero. Therefore its input resistance is extremely high, much higher than that of a bipolar junction transistor (BJT), whose base draws current. Hence option (a) is correct. Options (b) and (c) are incorrect because they describe a much lower input resistance than a MOSFET actually has, and (d) is also incorrect.
A thyristor chopper is preferred over other choppers because it
A)
provides static switching
B)
is economical
C)
can be manufactured easily
D)
none of these
A thyristor chopper is preferred mainly because it is economical compared with other chopper implementations. Thyristors are rugged, reliable, and relatively low-cost devices for high-power switching. Option (a) is not the best reason because all choppers are static electronic switches by nature. Option (c) is not the key advantage, since ease of manufacture is not the primary basis for preference. Therefore, the correct answer is (b) is economical.
The numbers of thyristors required for 1-phase to 1-phase cyloconverter of the mid-point type and for 3-phase to 3-phase 3-pulse type are respectively
A)
4 and 6
B)
4 and 4
C)
4 and 9
D)
4 and 18
For a 1-phase to 1-phase mid-point cycloconverter, two full-wave converters are used, and each needs 2 thyristors, so total = 4 thyristors. For a 3-phase to 3-phase 3-pulse cycloconverter, each 3-pulse converter uses 3 thyristors, and there are 6 such converters in the standard arrangement, so total = 18 thyristors. Hence the correct answer is 4 and 18.
The ASCII code is a
A)
5-bit code
B)
7-bit code
C)
9-bit code
D)
11-bit code
ASCII stands for American Standard Code for Information Interchange. The original ASCII standard uses 7 bits, allowing 128 characters (0 to 127). Therefore, the correct answer is 7-bit code. The other options are incorrect because ASCII is not a 5-bit, 9-bit, or 11-bit code.
Non-sinusoidal waveforms
A)
are departures from sine waveform
B)
have low mark-to-space ratio
C)
are much easier to generate
D)
are unfit for digital operation
A non-sinusoidal waveform is any waveform that is not a pure sine wave, so it is a departure from sine waveform. Option (b) is not a defining property, (c) is not generally true for all non-sinusoidal waveforms, and (d) is incorrect because many digital signals are non-sinusoidal and are widely used in digital operation.
The thyristor is turned off
A)
by switching off the voltage applied to the principal circuit and changing into reverse blocking mode
B)
by switching off the voltage applied to the gate circuit only
C)
by changing the thyristor into forward blocking state
D)
none of these
A thyristor (SCR) is turned off by reducing its anode current below the holding current and applying reverse bias or removing the main circuit voltage so it returns to the reverse blocking state. The gate terminal cannot turn it off; it only triggers turn-on. Hence option (a) is correct. Option (b) is wrong because gate voltage alone cannot turn off an SCR. Option (c) is incorrect because forward blocking is not the turn-off state.
An assembler in a computer system prepares
A)
machine-language program from a symbolic language program
B)
object program
C)
assembles computer instructions and data in the machine
D)
none of these
An assembler translates an assembly/symbolic language program into machine language. So option (a) is correct. Option (b) is incomplete because an assembler produces an object program as an intermediate/output form, but the standard definition asked here is the translation from symbolic language to machine language. Option (c) is incorrect because an assembler does not physically assemble instructions and data in the machine.
The highest voltage gain can be obtained from a .............. configuration
A)
CC
B)
CE
C)
CB
D)
both CE and CB
In a BJT, the common-emitter (CE) configuration provides the highest voltage gain among the three basic configurations. It offers both significant current gain and voltage gain, making it the most widely used amplifier configuration. Common-collector (CC) has voltage gain less than 1, and common-base (CB) has good voltage gain but generally less practical overall than CE for this purpose. Therefore, the correct answer is CE.
In microprocessors, return from a subroutine is affected by
A)
a jump instruction
B)
an RST instruction
C)
a RET instruction
D)
a hardware interrupt signal
In microprocessors, a subroutine is entered using a CALL instruction, and it is returned from using a RET (return) instruction. RET pops the saved return address from the stack and transfers control back to the instruction after the CALL. A jump instruction only transfers control unconditionally, RST is a restart/call-like instruction, and a hardware interrupt signal invokes an interrupt service routine rather than directly returning from a subroutine.
When used in a circuit, the Zener diode is always
A)
forwarded biased
B)
connected in series
C)
troubled by overheating
D)
reverse biased
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 that is not its normal circuit use. The other options are incorrect because a Zener diode is not defined by being connected in series, and overheating is not its intended operating condition.
A p-n junction photodiode is
A)
operated in forwarded region
B)
encased in an opaque package
C)
a very fast photo detector
D)
dependent on thermally generated minority carriers
A p-n junction photodiode is used as a light detector and is typically operated in reverse bias for fast response. Because of the depletion region and reverse-bias operation, it can respond quickly to changes in light, making it a very fast photo detector. Option (a) is wrong because photodiodes are not normally operated in forward bias. Option (b) is wrong because they must receive light, so they are not placed in an opaque package. Option (d) is wrong because that describes a device whose operation depends mainly on thermally generated minority carriers, not a photodiode.
According to Boolean algebra, (A + Ā) equals
A)
A
B)
1
C)
0
D)
Ā
By the complement law in Boolean algebra, a variable ORed with its complement equals 1: A + Ā = 1. So the correct option is (b). The other options are incorrect because A + Ā is not A, not 0, and not Ā.
An FET consists of a
A)
source
B)
drain
C)
gate
D)
all of these
An FET (Field Effect Transistor) has three main terminals: source, drain, and gate. The source supplies carriers, the drain collects them, and the gate controls the channel conductivity. Therefore, it consists of all of these.
The basic function of an electronic filter circuit in radio communication is to
A)
replace tuning circuits
B)
eliminate ripples in D.C. power supplies
C)
separate different frequencies in a composite signal
D)
divert RF currents out of a given circuit
An electronic filter in radio communication is used to pass desired frequency components and reject unwanted ones, i.e., to separate different frequencies in a composite signal. Option (b) refers to power-supply filtering, which is a specific application, not the basic function in radio communication. Option (a) is incorrect because filters do not simply replace tuning circuits. Option (d) describes a special RF bypassing function, not the general basic purpose of a filter.