← MES Jr. Grade
Past Questions
The Y plates of a CRO are excited by a voltage 2sin(100t) and X plates are not connected. The display would be
A)
a vertical line
B)
a horizontal line
C)
a sine wave
D)
a slanting line
In a CRO, the Y-plates control vertical deflection and the X-plates control horizontal deflection. Here, the Y-plates are given an AC voltage 2sin(100t), so the spot moves up and down vertically. Since the X-plates are not connected, there is no horizontal deflection, so the beam stays at a fixed X-position. Therefore, the display is a vertical line. A horizontal line would require only X-deflection, and a sine wave or slanting line would need both X and Y inputs.
IEEE488 standard is based on the transmission of
A)
4 bit
B)
8 bit
C)
16 bit
D)
24 Bit
IEEE-488 (also called GPIB) is a parallel digital interface standard that uses an 8-bit data bus for transmission. Hence, it is based on the transmission of 8 bits. The other options do not match the standard data width used in IEEE-488.
A 0 – 200V voltmeter has a sensitivity of 1KΩ/V. The resistance of the voltmeter is
A)
100KΩ
B)
200KΩ
C)
1KΩ
D)
50KΩ
Sensitivity of a voltmeter = resistance per volt = 1 kΩ/V. For a 0–200 V voltmeter, total resistance = 1 kΩ/V × 200 V = 200 kΩ. Hence the correct option is (b).
For carbon resistors what is the color for 5?
A)
green
B)
black
C)
orange
D)
gray
In the standard resistor color code, the digit 5 is represented by green. The sequence is: 0 black, 1 brown, 2 red, 3 orange, 4 yellow, 5 green, 6 blue, 7 violet, 8 gray, 9 white. Therefore, the correct option is green. Black is 0, orange is 3, and gray is 8.
An electrostatic Voltmeter is suitable for measuring
A)
low voltage at high frequency
B)
high voltage
C)
low voltage at low frequency
D)
all ac and dc voltages
An electrostatic voltmeter works on the electrostatic force between charged plates, so it draws negligible current and is mainly used for measuring very high voltages. It is not suitable for low voltages because the deflection is too small. It can be used for both AC and DC, but its standard application is high-voltage measurement. Hence, the correct option is (b) high voltage.
The peak inverse voltage is applied across a diode when it is
A)
on
B)
on a heat sink
C)
reverse biased
D)
forward biased
Peak inverse voltage (PIV) is the maximum reverse voltage a diode can withstand without breakdown. Therefore, it is applied when the diode is reverse biased. In forward bias, the diode conducts and the reverse voltage condition does not occur. Options (a), (b), and (d) do not describe the reverse-bias condition relevant to PIV.
Resistance of a wire is r ohms. The wire is stretched to double its length then its resistance in ohms is
A)
r/2
B)
4r
C)
2r
D)
r/4
For a wire, resistance R = ρL/A. When the wire is stretched to double its length, its volume remains constant, so the cross-sectional area becomes half. Thus new resistance R' = ρ(2L)/(A/2) = 4ρL/A = 4r. Therefore, the resistance becomes 4r.
The electrostatic nature of ionic bond makes it
A)
directional
B)
non-directional
C)
weak
D)
related to group IV element
An ionic bond is formed by electrostatic attraction between oppositely charged ions. Since this attraction acts equally in all directions around the ions, ionic bonding is non-directional. It is not directional like covalent bonds. It is also generally strong, so option (c) is incorrect, and it is not specifically related to group IV elements, so option (d) is incorrect.
JFET can operate in
A)
depletion mode and enhancement mode
B)
depletion mode only
C)
enhancement mode only
D)
neither enhancement nor depletion mode
A JFET (Junction Field Effect Transistor) is a normally ON device. Its channel conducts at zero gate bias, and applying reverse gate voltage only depletes the channel and reduces current. It does not operate in enhancement mode. Therefore, the correct answer is depletion mode only.
If current through the coil of a electromagnet is doubled, then the magnetic field around the coil is
A)
halved
B)
doubled
C)
four folded
D)
same
For an electromagnet coil, the magnetic field strength is directly proportional to the current flowing through the coil (B ∝ I), assuming the number of turns and core remain the same. So, if the current is doubled, the magnetic field also doubles. Hence, option (b) is correct. The other options are incorrect because the field does not become half, four times, or remain unchanged when current is doubled.
The main constituent of glass is
A)
SiO2
B)
B2O3
C)
Al2O3
D)
none of these
Glass is mainly made from silica, i.e., silicon dioxide (SiO2). In ordinary glass, silica is the principal constituent, while other oxides such as sodium oxide and calcium oxide are added to modify its properties. B2O3 is the main constituent of borosilicate glass, and Al2O3 is not the main constituent of common glass.
The current in a circuit is measured using a 150:1 CT. If the ohm-meter reads 0.6A, the circuit current is
A)
250A
B)
90A
C)
156A
D)
144A
A 150:1 current transformer (CT) means the primary current is 150 times the secondary current. If the ohm-meter reads 0.6 A on the secondary side, then circuit current = 150 × 0.6 = 90 A. However, since 90 A is not among the options and the option set includes 144 A, the question likely intends a different interpretation or contains a typo. Based on the given CT ratio and reading, the mathematically correct answer is 90 A, which corresponds to option (b), not (d).
It is required to measure temperature in the range of 1300º–1520ºC. The most suitable thermo couple is
A)
chromel- constantan
B)
iron-constantan
C)
chromel-alumel
D)
platinum-rhodium
For very high temperatures like 1300°C to 1520°C, a noble-metal thermocouple is required. Platinum-rhodium thermocouples are suitable for this range because they can withstand high temperatures and provide stable, accurate measurements. Chromel-constantan and iron-constantan are used for much lower temperature ranges, while chromel-alumel is generally suitable up to about 1200°C, which is below the required range.
Vulcanized rubber
A)
Is produced from trans-polyisoprene
B)
Is alternatively known as neoprene
C)
Contains about 20% sulphur by weight
D)
Is produced from cis-polyisoprene
Vulcanized rubber is made from natural rubber, which is cis-1,4-polyisoprene. Vulcanization is the process of heating rubber with sulphur to improve its strength and elasticity, but the base polymer remains cis-polyisoprene. Option (a) is wrong because trans-polyisoprene is gutta-percha, not natural rubber. Option (b) is wrong because neoprene is a different synthetic rubber. Option (c) is wrong because vulcanized rubber does not contain about 20% sulphur; typical sulphur content is much lower.
Dielectric strength of impregnated paper is
A)
40-50 KV/cm
B)
200- 300 KV/cm
C)
500-600 KV/cm
D)
800-900 KV/cm
Impregnated paper has a dielectric strength in the range of about 200 to 300 kV/cm. This is much higher than plain paper because impregnation removes air gaps and improves insulation. The other options are either too low or unrealistically high for impregnated paper.
Eutectoid transformation in an alloy is a reaction of which type?
A)
Solid ↔ liquid
B)
liquid ↔ liquid
C)
solid ↔solid
D)
any of these
A eutectoid transformation is a solid-state phase transformation in which one solid phase changes into two different solid phases on cooling, or the reverse on heating. Therefore, it is a solid ↔ solid reaction. Option (a) is a solid–liquid reaction, and option (b) is not a eutectoid transformation. Hence, the correct answer is (c).
When bias is applied to a varicap diode is increased, its capacitance
A)
decreases
B)
increases
C)
remains constant
D)
increases than decreases
A varicap (varactor) diode works as a voltage-controlled capacitor. When the reverse bias is increased, the depletion layer widens, so the junction capacitance decreases. Hence, the correct answer is (a) decreases.
Which of the following terms is not associated with a S/H circuit?
A)
conversion time
B)
acquisition time
C)
aperture time
D)
sample time
A sample-and-hold (S/H) circuit is associated with sampling-related terms such as acquisition time, aperture time, and sample time. These describe how the input is captured and held. Conversion time, however, belongs to the ADC process after sampling, not to the S/H circuit itself. Hence, it is the term not associated with a S/H circuit.
Intrinsic semiconductor are those which
A)
are available locally
B)
are in the purest form
C)
have more electrons than holes
D)
have zero energy gap
An intrinsic semiconductor is a pure semiconductor with no intentional impurities (doping). In such materials, the number of electrons equals the number of holes. Option (a) is unrelated, (c) describes an extrinsic imbalance, and (d) is incorrect because intrinsic semiconductors do have a small but non-zero energy gap.
At higher forward voltages, a junction diode is likely to
A)
burnout
B)
get saturated
C)
suffer breakdown
D)
become noisy
At higher forward voltages, a junction diode conducts a very large current. This excessive current causes overheating and can damage the diode, leading to burnout.
Why others are incorrect:
- (b) get saturated: saturation is not the usual failure mode of a forward-biased diode.
- (c) suffer breakdown: breakdown is typically associated with reverse bias, not forward bias.
- (d) become noisy: noise may occur in electronic devices, but it is not the primary effect of excessive forward voltage in a diode.
The four stripes of a resistor are yellow-violet-orange-gold. The value of the resistance should be
A)
470Ω ± 5%
B)
47KΩ ± 5%
C)
47MΩ ± 5%
D)
47KΩ ± 10%
For a 4-band resistor, the first two bands give the significant digits, the third band is the multiplier, and the fourth band is the tolerance. Yellow = 4, Violet = 7, Orange = ×10^3, and Gold = ±5%. So the resistance is 47 × 10^3 ohms = 47 kΩ with ±5% tolerance. Hence, option (b) is correct. Option (a) would correspond to 470 Ω, which is not correct here; option (c) is too large; option (d) has the wrong tolerance.
To increase the Q factor of a coil, the wire should be
A)
long
B)
thin
C)
thick
D)
long & thin
The Q factor of a coil is inversely related to its resistance. Using a thicker wire reduces the resistance of the coil, thereby increasing the Q factor. A thin wire has higher resistance, so it lowers Q. Hence, the correct answer is thick.
A digital frequency counter can be converted to DVM by addition of a suitable
A)
VCO
B)
D/A converter
C)
power amplifier
D)
Op-Amp
A digital frequency counter measures frequency by counting pulses. To convert it into a digital voltmeter (DVM), the input voltage is first converted into a proportional frequency using a voltage-to-frequency converter, typically a VCO. The counter then measures this frequency and displays the corresponding voltage. A D/A converter, power amplifier, or op-amp alone cannot perform this conversion.
In the system of the above question, if ξ > 1, the system is
A)
under-damped
B)
over-damped
C)
absolutely damped
D)
critically damped
In a standard second-order control system, the damping ratio is denoted by ξ (or ζ). If ξ > 1, the system is overdamped. Such a system returns to equilibrium without oscillation, but more slowly than a critically damped system. For reference: ξ < 1 is underdamped, ξ = 1 is critically damped, and ξ > 1 is overdamped. Hence, option (b) is correct.
A position control system is
A)
a process control system
B)
an automatic regulatory system
C)
a servomechanism
D)
a stochastic control system
A position control system is used to control the position of a mechanical element by comparing the actual position with the desired position and correcting the error automatically. Such systems are called servomechanisms. It is not a process control system, which regulates process variables like temperature or pressure, nor an automatic regulatory system in the general sense, and it is not a stochastic control system, which deals with random processes.