← MES Jr. Grade
Past Questions — 2014
Width of energy bands depends on which of the following?
A)
Temperature
B)
Pressure
C)
Relative freedom of electrons in the crystal
D)
Mass of atom in the material
The width of an energy band is determined by the extent of overlap between atomic orbitals in a crystal, which reflects how freely electrons can move in the lattice. Greater electron freedom (stronger overlap) leads to wider bands. Temperature and pressure may affect band structure indirectly in some cases, but the basic dependence is on the relative freedom of electrons in the crystal. The mass of the atom is not the determining factor.
If R, XL and XC be the resistance, inductive reactance and capacitive reactance of a series resonant circuit then current is
A)
Minimum and in phase with voltage given by I=V/R
B)
Maximum and in phase with voltage given by I=V/R
C)
Minimum and lagging in phase with voltage given by I=V/XL
D)
Maximum and leading in phase with voltage given by I=V/XC
In a series resonant circuit, resonance occurs when XL = XC. The inductive and capacitive reactances cancel each other, so the net reactance becomes zero and the circuit impedance is minimum, equal to R only. Since I = V/Z, the current becomes maximum: I = V/R. Also, because the circuit is purely resistive at resonance, current is in phase with the voltage. Hence option (b) is correct. Options (a), (c), and (d) are incorrect because at resonance the current is not minimum, and it neither lags nor leads the voltage.
Which one of the following materials can be used for permanent magnets?
A)
Alnico
B)
Barium ferrite
C)
Carbon steel
D)
Iron – cobalt alloy
Permanent magnets require materials with high retentivity and high coercivity so that they retain magnetism after the magnetizing field is removed. Alnico is a well-known permanent magnet material. Barium ferrite is also used for permanent magnets, but in standard single-correct MCQs of this type, Alnico is the expected answer. Carbon steel is an older magnet material but is not as suitable as Alnico, and iron-cobalt alloys are mainly used where very high saturation flux density is needed, not as the typical answer for permanent magnets.
An electromagnetic field is radiated from
A)
A stationary point charge
B)
A capacitor with dc voltage
C)
A conductor carrying a dc current
D)
An oscillating dipole
Electromagnetic radiation is produced by accelerating charges or time-varying currents. An oscillating dipole has charges moving back and forth, so it continuously creates changing electric and magnetic fields that propagate as electromagnetic waves. A stationary point charge does not radiate. A capacitor with dc voltage and a conductor carrying dc current produce static fields, not radiation.
Megger is an instrument used to measure
A)
very low resistance
B)
insulation resistance
C)
Q-factor of a coil
D)
inductance of a coil
A megger (megohmmeter) is used to measure very high resistance, especially the insulation resistance of cables, motors, and electrical installations. It is not used for very low resistance, Q-factor, or inductance measurements. Therefore, the correct answer is insulation resistance.
The insulating materials meant for most of electronic equipment should possess high
A)
dielectric strength
B)
mechanical strength
C)
thermal stability
D)
all of these
Insulating materials used in electronic equipment should have high dielectric strength so they can withstand electric stress without breakdown. They should also have good mechanical strength to endure handling and mounting, and high thermal stability so they do not deteriorate under heat generated during operation. Therefore, the correct choice is all of these.
Series connection of current sources is not allowed because it violates
A)
Principle of energy conservation
B)
Ohm’s law
C)
KCL
D)
KVL
Current sources enforce a fixed current. In a series connection, the same current must flow through all elements, but ideal current sources may demand different currents. At the junction between them, this creates a conflict with Kirchhoff’s Current Law (KCL), which requires the algebraic sum of currents at a node to be zero. Hence, series connection of current sources is not allowed. KVL, Ohm’s law, and energy conservation are not the primary reason for this restriction.
A moving coil galvanometer is made into a dc ammeter by connecting
A)
a low resistance across the meter
B)
a high resistance in series with meter
C)
a pure inductance across the meter
D)
a capacitor in series with the meter
A moving coil galvanometer is converted into a DC ammeter by connecting a low resistance shunt in parallel across the meter. This shunt carries most of the current, protecting the galvanometer and allowing measurement of larger currents. A high resistance in series is used to convert it into a voltmeter, while inductance or capacitor connections are not used for this purpose.
Electromagnetic waves may be diffracted
A)
By reflection from the ground
B)
When encountered with a spherical wave front
C)
Around the edge of a sharp obstacle
D)
While passing through a large slot
Diffraction is the bending/spreading of waves when they pass around an obstacle or through an aperture. Electromagnetic waves are diffracted around the edge of a sharp obstacle. Reflection from the ground is not diffraction, a spherical wave front is not the cause of diffraction, and a large slot would produce very little diffraction because diffraction is significant when the opening is comparable to the wavelength.
Two light bulbs P and Q are identical in all respects, except that P’s filament is thicker than Q’s. If the same potential difference is applied to each, then
A)
P will burn brighter because it has the greater resistance
B)
Q will burn brighter because it has the greater resistance
C)
P will burn brighter because it has the lower resistance
D)
Q will burn brighter because it has the lower resistance
A thicker filament has a larger cross-sectional area, so its resistance is lower. For the same applied potential difference, the power dissipated is P = V^2 / R. Hence the bulb with lower resistance dissipates more power and glows brighter. Therefore, bulb P burns brighter. Options (a) and (b) are wrong because brightness is not greater for higher resistance at fixed voltage, and (d) is wrong because Q has the higher, not lower, resistance.
A single-phase energy meter is operating on 230 V, 50 Hz, supply with a load of 20 A for two hours at unity power factor. The meter makes 1380 revolutions in that period. The meter constant is
A)
695 rev/KWh
B)
150 rev/ KWh
C)
0.15 rev/KWh
Energy consumed by the load = V × I × t × power factor = 230 × 20 × 2 × 1 = 9200 Wh = 9.2 kWh.
The meter makes 1380 revolutions for 9.2 kWh, so meter constant = 1380 / 9.2 = 150 rev/kWh? Wait, that is the number of revolutions per kWh from the given data. However, the options include 150 rev/kWh, which matches the calculation.
So the correct meter constant from the given values is 150 rev/kWh, not 695 rev/kWh. If the question intended 'meter reading constant' in terms of kWh per revolution, it would be 1/150 kWh/rev. Among the given options, (b) is correct.
With increase in temperature, magnetic susceptibility of a ferromagnetic material will
A)
Increase
B)
Decrease
C)
Increase initially and then decrease
D)
Remain constant
In a ferromagnetic material, thermal agitation increases as temperature rises. This disturbs the alignment of magnetic domains, so the net magnetization reduces and magnetic susceptibility decreases. Near the Curie temperature, the susceptibility drops sharply and the material eventually becomes paramagnetic. Hence, the correct option is (b) Decrease.
What is the value of total electric flux coming out of a closed surface?
A)
Zero
B)
Equal to volume charge density
C)
Equal to the total charge enclosed by the surface
D)
Equal to the surface charge density.
By Gauss’s law, the total electric flux through any closed surface is proportional to the net charge enclosed by that surface: \(\Phi_E = Q_{enclosed}/\varepsilon_0\). Among the given options, the correct statement is that it is equal to the total charge enclosed by the surface. Option (a) is only true when no net charge is enclosed. Options (b) and (d) are incorrect because flux is not equal to charge density.
A 3-phase, star-connected symmetrical load consumes P watts of power from a balanced supply. If the same load is connected in delta to the same supply, the power consumption will be
A)
P watts
B)
3 P watts
C)
3 P watts
D)
P/3 watts
For the same symmetrical load, each phase impedance remains the same. In star connection, phase voltage is V_L/\u221a3, so total power is P = 3(V_L/\u221a3)I_ph cos\u03c6. In delta connection, each phase gets full line voltage V_L, so phase current becomes 3 times the star phase current for the same impedance. Hence total power becomes 3 times the star-connected power. Therefore, the power consumption is 3P watts.
For which one of the following materials is the Hall coefficient zero?
A)
Metal
B)
Insulator
C)
Intrinsic semiconductor
D)
Alloy
The Hall coefficient becomes zero when the material has no net Hall voltage due to cancellation of charge-carrier effects. In alloys, the Hall coefficient is often taken as zero in standard exam context because they behave like metals with very small or negligible Hall effect compared to pure metals and semiconductors.
Why others are not correct:
- Metal: generally has a non-zero Hall coefficient.
- Insulator: Hall effect is not typically considered meaningful due to lack of free carriers.
- Intrinsic semiconductor: has a non-zero Hall coefficient because both electrons and holes contribute, but not in a way that makes it zero.
So the expected answer is Alloy.
For measurement of mutual inductance we can use
A)
Anderson bridge
B)
Maxwell’s bridge
C)
Heaviside bridge
D)
Any of these
Mutual inductance is commonly measured using the Anderson bridge. Maxwell’s bridge is mainly used for measuring unknown inductance in terms of a standard capacitor and resistors, while the Heaviside bridge is not the standard choice for mutual inductance measurement. Therefore, the correct answer is Anderson bridge.
Hall’s effect is used to measure
A)
electric field intensity
B)
magnetic field intensity
C)
carrier concentration
D)
none of these
Hall effect is commonly used to determine the type and concentration of charge carriers in a semiconductor or conductor. When a current-carrying material is placed in a magnetic field, a Hall voltage is produced perpendicular to both current and magnetic field. From this Hall voltage, carrier concentration can be calculated. It is not primarily used to measure electric field intensity or magnetic field intensity.
Which of the following bridges is used to measure frequency?
A)
Anderson bridge
B)
Wein bridge
C)
De Sauty’s bridge
D)
none of these
Wien (Wein) bridge is used for measuring frequency, especially in audio-frequency circuits. Anderson bridge is used to measure self-inductance, and De Sauty’s bridge is used to compare capacitances. Therefore, the correct answer is Wein bridge.
A milliammeter can be used as a voltmeter by connecting
A)
a low resistance in parallel with the instrument
B)
a high resistance in parallel with the instrument
C)
a low resistance in series with the instrument
D)
a high resistance in series with the instrument
A milliammeter is a low-resistance current-measuring device. To use it as a voltmeter, the current through it must be made very small while measuring voltage. This is done by connecting a high resistance in series with the instrument, called a multiplier. The series resistance limits current and allows the meter to measure higher voltages safely. A parallel resistance would not convert it into a voltmeter.
The hysteresis loop for the material of the core of a transformer should be
A)
Short and narrow
B)
Tall and narrow
C)
Short and wide
D)
Tall and wide
A transformer core should have low hysteresis loss, because the magnetic flux in the core keeps reversing. Hysteresis loss is proportional to the area of the hysteresis loop, so the ideal core material should have a loop with a small area. A short and narrow loop means low coercivity and low retentivity, which is suitable for transformer cores. The other options imply a larger loop area and therefore greater energy loss.
A series RLC circuit will have unity power factor if operated at a frequency of
A)
1/ LC
B)
1/LC
C)
1/2 LC
D)
2LC
For a series RLC circuit, unity power factor occurs at resonance, when inductive reactance equals capacitive reactance: XL = XC. This gives ω = 1/√LC, so the resonant frequency is f = ω/2π = 1/(2π√LC). Hence the correct option is (c). The other options do not represent the resonant frequency formula.
Ampere’s Circuital Law is analogous to __________ Law in electrostatics.
A)
Lenz’s
B)
Gauss’s
C)
Biot–Savart’s
D)
Faraday’s
Ampere’s Circuital Law in magnetostatics relates the line integral of magnetic field around a closed path to the current enclosed. This is analogous to Gauss’s Law in electrostatics, which relates the electric flux through a closed surface to the charge enclosed. Both are integral laws connecting a field to its source. The other options are not analogous laws in electrostatics: Lenz’s and Faraday’s laws are related to electromagnetic induction, and Biot–Savart’s law gives the magnetic field due to a current element.
Dielectric strength of a material depends on
A)
Temperature
B)
Thickness
D)
All of these
Dielectric strength is the maximum electric field a material can withstand without breakdown. It depends on factors such as temperature and thickness of the dielectric. Since both listed factors affect dielectric strength, the correct answer is 'All of these'.
The charge on an isolated conductor resides
A)
At the conductor surface
B)
Inside the conductor
C)
Partly at the surface and partly inside the conductor
D)
None of these
In electrostatic equilibrium, the electric field inside an isolated conductor is zero. Therefore, any excess charge moves freely and resides only on the outer surface of the conductor. Hence, option (a) is correct. Options (b) and (c) are incorrect because charge does not remain inside the conductor in electrostatic equilibrium.
The gravity controlled instrument has crowded scale because current is proportional to
A)
balancing weight
B)
deflection angle
C)
sine of deflection angle
D)
None of these
In a gravity-controlled instrument, the controlling torque is provided by gravity and is proportional to sin(θ), where θ is the deflection angle. At equilibrium, deflecting torque is proportional to current, so current is also proportional to sin(θ). Since sin(θ) changes slowly near the ends of the scale, the scale becomes crowded there. Hence the correct answer is sine of deflection angle.