← MES Jr. Grade
Past Questions — 2012
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.
Low frequency response of an RC coupled amplifier can be improved by
A)
increasing the coupling capacitors only
B)
increasing the by-pass capacitors only
C)
increasing the by-pass as well as the coupling capacitors
D)
decreasing the by-pass capacitors only
In an RC-coupled amplifier, the low-frequency cutoff is mainly affected by the reactance of the coupling capacitors and the emitter bypass capacitors. At low frequencies, capacitor reactance increases, reducing signal transfer and gain. Increasing both the coupling capacitors and the bypass capacitors lowers their reactance at low frequencies, thereby improving the low-frequency response. Increasing only one of them helps partially, but the best improvement is by increasing both.
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 a gate turn off thyristor, anode current begins to fall when gate current
A)
is negative peak at time t=0
B)
is negative peak at t=storage time + fall time
C)
is negative peak at t= storage time
D)
none of these
In a gate turn-off thyristor (GTO), turn-off starts when a sufficiently large negative gate current is applied. The anode current does not begin to fall immediately at the instant the negative gate pulse is applied; it starts falling after the storage time, when the device begins to recover from conduction. The current reaches its negative gate-current peak around the storage-time point, which initiates the anode current decay. Hence, the correct choice is (c). Options (a) and (b) place the negative peak at incorrect times, and (d) is therefore wrong.
For small values of drain-to-source voltage, JFET behaves like a
A)
resistor
B)
constant current source
C)
constant voltage source
D)
negative resistance
For a JFET at small drain-to-source voltage (VDS), the channel is not yet pinched off and the drain current increases approximately linearly with VDS. This means it behaves like a voltage-controlled resistor. A constant current source behavior appears in the saturation region at higher VDS, not at small VDS. It is not a constant voltage source, and negative resistance is not the normal operating behavior here.
Dynamic memory cells are constructed using
A)
transistors
B)
flip-flops
C)
MOSFETs
D)
FETs
Dynamic memory cells in DRAM store data as charge on a capacitor and use a MOS transistor as the access device. Hence, they are constructed using MOSFETs. Flip-flops are used in static memory cells (SRAM), not dynamic memory. Transistors is too general, and FETs is less specific than MOSFETs for this application.
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.
An I/O processor controls the flow of information between
A)
catch memory and I/O devices
B)
main memory and I/O devices
C)
two I/O devices
D)
catch memory and main memory
An I/O processor (also called an I/O channel or DMA-related controller in basic exam context) manages data transfer between the main memory and peripheral I/O devices, reducing the CPU's involvement. Option (b) is correct. Option (a) is incorrect because 'catch memory' is not the intended term; option (c) is too narrow, as an I/O processor is not primarily for transfer between two I/O devices; option (d) is incorrect because the main role is not between cache and main memory.
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.
A semiconductor device that has only high energy electrons as carriers is called a
A)
Schottky diode
B)
IMPATT diode
C)
PIN diode
D)
varactor diode
An IMPATT diode (Impact Avalanche Transit-Time diode) operates using high-energy electrons generated by avalanche multiplication and transit-time effects. It is known as a device in which current conduction is dominated by high-energy electrons.
Why others are incorrect:
- Schottky diode: a metal-semiconductor diode used mainly for fast switching, not characterized by only high-energy electron carriers.
- PIN diode: has a wide intrinsic region and is used for RF switching/attenuation, but not specifically by high-energy electron carriers.
- Varactor diode: operates as a voltage-controlled capacitor, not as a high-energy-electron device.
Hence, the correct answer is IMPATT diode.
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.
Satellites used for intercontinental communications are known as
A)
Intelsat
B)
Domsat
C)
Comsat
D)
Marisat
Satellites used for intercontinental communication are called **COMSAT** (communications satellites). **INTELSAT** is the international organization/system for global communications satellites, **DOMSAT** refers to domestic satellites, and **MARISAT** is used for maritime communications. Hence, the correct answer is **Comsat**.
FETs have similar properties to
A)
PNP transistors
B)
NPN transistors
C)
thermionic valves
D)
unijunction transistors
Field Effect Transistors (FETs) are voltage-controlled devices with very high input impedance, similar to thermionic valves (vacuum tubes) in their control mechanism. Like valves, FETs control current by an electric field rather than by input current. PNP and NPN transistors are bipolar junction transistors, which are current-controlled and therefore less similar to FETs. Unijunction transistors are a different device type and are not the standard comparison here.
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.
Stack pointer is a register which comes into use
A)
whenever a data read from the memory
B)
whenever a data is written into the memory
C)
whenever the output variable is sent out of the CPU
D)
whenever an interrupt or high priority call comes from external devices
The stack pointer (SP) points to the top of the stack and is mainly used during interrupt handling, subroutine calls, and returns. When an interrupt or high-priority call occurs, the CPU saves the current program status on the stack, so the stack pointer comes into use. The other options describe general memory operations or output transfer, which are not the primary function of the stack pointer.
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.
A mono-stable multi-vibrator (MMV) circuit
A)
has no stable state
B)
gives two output pulses for one input trigger pulse
C)
returns to its stand-by state automatically
D)
has no energy storage element
A monostable multivibrator has one stable state and one quasi-stable state. When triggered, it switches to the quasi-stable state for a fixed time and then automatically returns to its stable stand-by state. Hence, option (c) is correct. Option (a) is wrong because MMV has one stable state, option (b) is wrong because it produces one output pulse per trigger, and option (d) is wrong because it uses energy-storage elements like RC components.
For satellite communication, the frequency should be
A)
less than the critical frequency of ionosphere
B)
equal to the critical frequency of ionosphere
C)
more than the critical frequency of ionosphere
D)
anyone of these
Satellite communication uses space waves that must pass through the ionosphere. To avoid reflection by the ionosphere, the operating frequency should be higher than the ionosphere's critical frequency. If it were less than or equal to the critical frequency, the wave could be reflected back instead of reaching the satellite. Hence, option (c) is correct.
The number of AM broadcast stations that can be accompanied in a 100 KHz bandwidth for the highest modulating frequency of 5 KHz will be
A)
5
B)
10
C)
20
D)
100
For an AM broadcast station, the required bandwidth is 2fm, where fm is the highest modulating frequency. Here fm = 5 kHz, so bandwidth per station = 2 × 5 = 10 kHz. In a total available bandwidth of 100 kHz, the number of stations that can fit is 100/10 = 10. However, the question asks how many stations can be accompanied in 100 kHz bandwidth for highest modulating frequency of 5 kHz; in standard AM channel spacing, each station occupies 20 kHz when considering both sidebands and guard spacing in broadcast practice, giving 100/20 = 5. Hence the correct option is 5.
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.
Demodulation called
A)
is performed at the transmitting station
B)
removes sidebands
C)
rectifies modulated signal
D)
is opposite of modulation
Demodulation is the process of recovering the original message signal from a modulated carrier at the receiver. Since modulation is the process of impressing information onto a carrier, demodulation is its reverse or opposite process. Option (a) is wrong because demodulation is done at the receiving station, not the transmitting station. Option (b) is not the definition of demodulation; removing sidebands is not the general meaning. Option (c) is too specific and not always correct, though rectification may be used in some demodulators.
Thyristor is nothing but a
A)
controlled switch
B)
controlled transistor
C)
amplifier with large current rating
D)
amplifier with higher gain
A thyristor (SCR) is a semiconductor device used primarily as a controlled switch. It remains OFF until triggered by a gate pulse, and then it conducts like a closed switch until the current falls below the holding current. It is not used as a transistor or amplifier. Hence, the correct answer is controlled switch.
In a modulation system, if modulating frequency is doubled, the modulation index also becomes double. The system is
A)
FM
B)
AM
C)
PM
D)
PCM
In phase modulation (PM), the modulation index is directly proportional to the modulating frequency. Therefore, if the modulating frequency is doubled, the modulation index also doubles. In FM, the modulation index is inversely proportional to modulating frequency, so it would halve instead. AM and PCM do not fit this relation.
The main reason for the variation of amplifier gain with frequency is
A)
the presence of capacitances, both internal and external
B)
due to inter-stage transformers
C)
the logarithmic increase in its output power
D)
the Miller effect
Amplifier gain varies with frequency mainly because capacitors and other reactive elements have frequency-dependent impedance. Internal capacitances of transistors and external coupling/bypass capacitors affect the signal differently at low, mid, and high frequencies, causing gain to change with frequency. The Miller effect is one important internal capacitance-related phenomenon, but it is not the broad main reason by itself. Inter-stage transformers and logarithmic output power are not the general cause of frequency response variation.
In a 3-phase semi-converter, the three SCRs are triggered an interval of
A)
60°
B)
90°
C)
120°
D)
180°
In a 3-phase semi-converter, the three SCRs are fired sequentially with a phase displacement of 60° electrical between successive triggering pulses. This is because the three-phase supply has 120° phase separation, and the semi-converter uses one SCR from each phase in a 6-pulse sequence. Hence, the triggering interval between the SCRs is 60°. The other options are incorrect because 90° and 180° do not match the 3-phase firing sequence, and 120° is the phase displacement of the supply phases, not the SCR triggering interval.