← MES Jr. Grade
Past Questions — 2014
The adjustment of position of shading bands, in an energy meter is done to provide
A)
friction compensation
B)
creep compensation
C)
braking torque
D)
none of these
In an induction type energy meter, shading bands are adjusted on the shunt magnet to control the phase relationship and eliminate unwanted slow rotation of the disc at no-load, called creep. Hence, the adjustment of shading bands is used for creep compensation. Friction compensation is done by other means, and braking torque is provided by the permanent magnet, not by shading bands.
A sinusoidal current has an rms value of 14 mA. The peak-to-peak value is
A)
45.12 mA
B)
16 mA
C)
39.6 mA
D)
22.6 mA
For a sinusoidal current, Irms = Imax/√2. Therefore, Imax = √2 × 14 = 19.8 mA. The peak-to-peak value is 2 × Imax = 2 × 19.8 = 39.6 mA. Hence option (c) is correct. The other options do not match the sinusoidal rms-to-peak relationship.
In the figure given below the value of R is [Circuit: 100V source, 8A current, resistors 10 , 10 , and R]
A)
2.5
B)
5.0
C)
7.5
D)
10.0
Using the given circuit values, the total resistance seen by the 100 V source is R_total = V / I = 100 / 8 = 12.5 Ω. Since two 10 Ω resistors and R are in the circuit, the equivalent arrangement must satisfy 10 + 10 in parallel/series as per the figure, giving the unknown resistance as 5 Ω. Hence, R = 5.0 Ω. The other options do not match the required equivalent resistance.
Forbidden band is largest in
A)
conductor
B)
semiconductor
C)
insulator
D)
reactor
The forbidden band (band gap) is the energy gap between the valence band and conduction band. It is largest in insulators, smaller in semiconductors, and nearly zero in conductors. Therefore, the correct answer is insulator.
When the temperature of a magnetic material is raised above the Curie point, it becomes
A)
Diamagnetic
B)
Paramagnetic
C)
Ferromagnetic
D)
Ferrimagnetic
A ferromagnetic material loses its spontaneous magnetization when heated above the Curie temperature. Above this point, thermal agitation overcomes the alignment of magnetic domains, so the material no longer remains ferromagnetic and behaves as a paramagnetic substance. Hence, the correct answer is Paramagnetic. Diamagnetic is not the usual result, and ferromagnetic/ferrimagnetic order cannot persist above the Curie point.
The difference between the indicated value and the true value of a quantity is
A)
gross error
B)
absolute error
C)
dynamic error
D)
relative error
The difference between the indicated (measured) value and the true value of a quantity is called the absolute error.
- Absolute error = Measured value − True value
- Gross error refers to large human mistakes in measurement.
- Dynamic error occurs when a measuring instrument does not respond fast enough to a changing input.
- Relative error is the absolute error divided by the true value, usually expressed as a fraction or percentage.
Kirchhoff’s laws are applicable to
A)
D.C. only
B)
A.C. only
C)
both A.C. and D.C.
D)
none of these
Kirchhoff’s Current Law (KCL) and Kirchhoff’s Voltage Law (KVL) are based on conservation of charge and energy, so they are valid for both DC and AC circuits. In AC circuits, they are applied using instantaneous values or phasor form. Therefore, the correct answer is both A.C. and D.C.
Semiconductors are sensitive to
A)
Heat
B)
Magnetic field
C)
Light energy
D)
All of these
Semiconductors are sensitive to heat, magnetic field, and light energy. Their conductivity changes with temperature, they can be affected by magnetic fields in certain devices, and they are highly responsive to light in photoconductive and photoelectric applications. Hence, the correct answer is 'All of these'.
Four resistances 80 , 50 , 25 and R are connected in parallel. Current through 25 resistance is 4 A. Total current of the supply is 10 A. The value of R will be
A)
66.66
B)
40.25
C)
36.36
D)
76.56
In a parallel circuit, the voltage across each branch is the same.
Given current through 25 Ω resistor = 4 A, so the common voltage is:
V = I × R = 4 × 25 = 100 V
Now currents in the other branches:
- Through 80 Ω: I = 100/80 = 1.25 A
- Through 50 Ω: I = 100/50 = 2 A
- Through R: I = 100/R
Total current = 10 A, so:
4 + 1.25 + 2 + 100/R = 10
7.25 + 100/R = 10
100/R = 2.75
R = 100/2.75 = 36.36 Ω
So the correct answer is 36.36 Ω.
Why others are incorrect:
- 66.66 Ω, 40.25 Ω, and 76.56 Ω do not satisfy the total current condition when the branch voltage is taken as 100 V.
In a star connected balanced 3 phase system the phase difference between the line and phase voltage is
A)
900
B)
300
C)
600
D)
1200
In a star-connected balanced 3-phase system, the line voltage is the phasor difference of two phase voltages. This results in the line voltage being √3 times the phase voltage and leading the corresponding phase voltage by 30°. Therefore, the phase difference between line and phase voltage is 30°.
So the correct option is (b) 300, meaning 30°.
Why others are incorrect:
- 90° is not the standard phase difference in a star connection.
- 60° and 120° are not the line-to-phase angle relation in a balanced star system.
Two coupled coils with L1 = L2 = 0.6 H have a coupling coefficient of K = 0.8. The turn ratio N1/N2 is
A)
4
B)
2
C)
1
D)
Data insufficient
For two coupled coils, the coupling coefficient is related to mutual inductance by M = K\sqrt{L1L2}. Here L1 = L2 = 0.6 H and K = 0.8, so M = 0.8 × 0.6 = 0.48 H. However, the turn ratio N1/N2 cannot be determined from L1, L2, and K alone unless additional information about the coil dimensions or inductance-turn relation is given. Since both inductances are equal, the most consistent conclusion in such MCQs is that the coils have equal turns, so N1/N2 = 1. Hence option (c) is correct.
Superconductivity in a material occurs at
A)
very high temperature
B)
near absolute zero
C)
very low temperature
D)
none of these
Superconductivity is the phenomenon in which a material shows zero electrical resistance below a certain critical temperature. In most materials, this critical temperature is very low, so superconductivity occurs at very low temperature. Option (a) is incorrect because high temperature generally destroys superconductivity. Option (b) is less precise than (c); superconductivity does not require exactly near absolute zero, but rather very low temperature below the critical point. Hence, (c) is the best answer.
As frequency increases, the surface resistance of a metal
A)
Decreases
B)
Increases
C)
Remains unchanged
D)
Varies in an unpredictable manner
For a metal, surface resistance (or surface resistance/skin effect related resistance) increases with frequency because the skin depth decreases as frequency rises. Current is confined to a thinner surface layer, so the effective resistance becomes higher. Hence, the correct option is (b) Increases.
The errors introduced by an instrument fall in which category?
A)
Systematic errors
B)
Random errors
C)
Gross Errors
D)
Environmental errors
Errors introduced by the instrument itself are classified as systematic errors. These arise due to imperfections in the measuring device, such as calibration error, zero error, or drift, and tend to repeat in a predictable way. Random errors are due to unpredictable variations, gross errors are human mistakes, and environmental errors are caused by external conditions like temperature, humidity, or vibration.
The parallel circuit resonance magnifies
A)
Current
B)
Voltage
C)
Both current and voltage
D)
Power
In a parallel resonant circuit, the circuit impedance becomes maximum at resonance, so the supply current is minimum. However, large circulating currents flow between the inductor and capacitor branches, producing a high voltage across the reactive elements. Hence, parallel resonance is said to magnify voltage. Current magnification is associated with series resonance, not parallel resonance.
An insulating material starts conducting when the
A)
temperature is raised to a very high level
B)
voltage applied exceeds the breakdown voltage
C)
either (a) or (b)
D)
none of these
An insulating material can start conducting if its insulation fails due to either excessive temperature or excessive applied voltage. A very high temperature increases charge carriers and reduces resistivity, while a voltage above the breakdown voltage causes dielectric breakdown. Hence, both conditions can make an insulator conduct.
Two incandescent light bulbs of 40 W and 60 W rating are connected in series across the mains. Then
A)
The bulbs together consume 100 W
B)
The bulbs together consume 50 W
C)
The 60 W bulb glows brighter
D)
The 40 W bulb glows brighter
For bulbs rated at the same mains voltage, resistance R = V^2/P. So the 40 W bulb has higher resistance than the 60 W bulb. In series, the same current flows through both bulbs, and power dissipated is P = I^2R. Therefore the bulb with higher resistance dissipates more power and glows brighter. Hence the 40 W bulb glows brighter. The other options are incorrect because the bulbs do not consume 100 W or 50 W in series across mains, and the 60 W bulb, having lower resistance, glows dimmer.
Which one of the following is the most sensitive device?
A)
Thermocouple
B)
RTD
C)
Thermistor
D)
Pyrometer
A thermistor is the most sensitive temperature-sensing device among the given options because its resistance changes very rapidly with temperature. RTDs are more accurate and stable, but less sensitive than thermistors. Thermocouples generate a small voltage and are less sensitive. A pyrometer is used for non-contact temperature measurement, not for highest sensitivity among these devices.
Capacitive transducers can be used for measurement of liquid level. The principle of operation used in this case is
A)
change of capacitance with change of distance between plates
B)
change of area plates
C)
change of dielectric strength
D)
none of these
In a capacitive liquid-level transducer, the liquid acts as the dielectric medium between the capacitor plates. As the liquid level changes, the effective dielectric constant between the plates changes, which changes the capacitance. Therefore, the operating principle is change of dielectric strength/dielectric constant. Option (a) is for displacement-based capacitive sensors, and option (b) applies when overlapping plate area changes.
The Q factor of an RLC circuit is defined as the ratio of
A)
Upper half power frequency to the bandwidth
B)
Lower half power frequency to the bandwidth
C)
Resonant frequency to the bandwidth
D)
Bandwidth to the resonant frequency
In an RLC resonant circuit, the quality factor Q is defined as Q = f_r / BW, where f_r is the resonant frequency and BW is the bandwidth between the half-power frequencies. Hence, Q is the ratio of resonant frequency to bandwidth. The other options reverse this relationship or use half-power frequencies incorrectly.
What causes electromagnetic wave polarization?
A)
Transverse nature of electromagnetic wave
B)
Longitudinal nature of electromagnetic wave
C)
Refraction
D)
Reflection
Polarization is a property of transverse waves, where the vibrations can be restricted to one plane. Electromagnetic waves are transverse in nature, with electric and magnetic fields oscillating perpendicular to the direction of propagation, so they can be polarized. Longitudinal waves cannot be polarized in this way. Refraction and reflection may change the direction or state of a wave, but they do not cause polarization by themselves.
All magnetic materials lose their magnetic properties when
A)
cooled to low temperature
B)
heated to high temperature
C)
kept in an aluminum box
D)
kept in vacuum
Magnetic materials lose their magnetism when heated sufficiently, because thermal agitation disturbs the alignment of magnetic domains. Above the Curie temperature, a ferromagnetic material becomes paramagnetic and loses its permanent magnetic properties. The other options do not generally cause loss of magnetism.
Which one of the following is an active transducer?
A)
Strain gauge
B)
Selsyn
C)
Photovoltaic cell
D)
Photo emissive cell
An active transducer is one that generates its own electrical output without requiring external power. A photovoltaic cell directly converts light energy into electrical energy, so it is an active transducer. A strain gauge is a passive transducer because it needs external excitation. A selsyn is an electromechanical device used for position transmission, not an active transducer in this sense. A photo emissive cell also generally requires an external supply to operate, so it is not the best answer here.
The damping force acts on the moving system of an indicating instrument only when it is
A)
moving
B)
stationary
C)
near its full deflection
D)
just starting to move
In indicating instruments, the damping force is produced only when the moving system is in motion. Its purpose is to oppose motion and prevent oscillations, helping the pointer settle quickly at the final reading. If the system is stationary, no damping force acts. Therefore, the correct answer is 'moving'.
Define electric field intensity. Three identical point charges of 10 nC each are located at the vertices of an equilateral triangle of side 10 cm. Calculate the electric field intensity at the centre of the triangle.