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Maharashtra HSC Electrical Maintenance (Bifocal) study materials
Maharashtra HSC Electrical Maintenance (Bifocal) study resources

Maharashtra HSC Electrical Maintenance (Bifocal) practice questions

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Question 1Fundamentals of Electricity and Magnetism

In an electrical maintenance workshop, a resistor of 220 Ω carries a current of 0.5 A. What is the potential difference across the resistor?

  1. 440 V
  2. 110 V Correct answer.
  3. 220 V
  4. 55 V

Explanation

Ohm's law states that V = I × R, so the voltage equals 0.5 A multiplied by 220 Ω, which gives 110 V. The resistance value alone does not give the voltage; the current must be multiplied by it.

Question 2Fundamentals of Electricity and Magnetism

Three resistors of 6 Ω each are connected in parallel. What is the equivalent resistance of the combination?

  1. 6 Ω
  2. 3 Ω
  3. 2 Ω Correct answer.
  4. 18 Ω

Explanation

For parallel resistors the reciprocal of the equivalent resistance is the sum of the reciprocals, so 1/R = 1/6 + 1/6 + 1/6 = 3/6. This gives R = 2 Ω, which is smaller than any single branch resistance.

Question 3Fundamentals of Electricity and Magnetism

Which material is classified as a ferromagnetic substance in the context of magnetic circuits used in electrical machines?

  1. Rubber
  2. Copper
  3. Aluminium
  4. Iron Correct answer.

Explanation

Ferromagnetic materials such as iron and steel are strongly attracted by a magnet and can be magnetised easily, so they are used to form the magnetic core of machines. Copper, aluminium and rubber do not show this strong magnetisation behaviour.

Question 4Fundamentals of Electricity and Magnetism

A coil has an inductance of 0.4 H and the current through it changes at a rate of 5 A per second. What is the magnitude of the self-induced emf?

  1. 2 V Correct answer.
  2. 0.08 V
  3. 1.25 V
  4. 20 V

Explanation

Faraday's law for self-induction gives e = L × (di/dt), so the emf equals 0.4 H multiplied by 5 A/s, which is 2 V. The induced emf opposes the change in current according to Lenz's law.

Question 5Fundamentals of Electricity and Magnetism

Which instrument is connected in parallel with the load to measure the potential difference across it?

  1. Voltmeter Correct answer.
  2. Wattmeter
  3. Energy meter
  4. Ammeter

Explanation

A voltmeter is connected in parallel across the two points whose potential difference is required. It is designed with a very high resistance so that it draws negligible current from the circuit.

Question 6Fundamentals of Electricity and Magnetism

A 100 W lamp is operated for 10 hours. How much electrical energy does it consume?

  1. 0.1 kWh
  2. 10 kWh
  3. 1 kWh Correct answer.
  4. 100 kWh

Explanation

Energy in kilowatt-hours equals power in kilowatts multiplied by time in hours, so 0.1 kW × 10 h = 1 kWh. This is the unit normally used for billing domestic electricity consumption.

Question 7Fundamentals of Electricity and Magnetism

In a purely capacitive AC circuit, what is the phase relationship between the applied voltage and the current?

  1. Current leads the voltage by 45 degrees
  2. Current lags the voltage by 90 degrees
  3. Current is in phase with the voltage
  4. Current leads the voltage by 90 degrees Correct answer.

Explanation

In a capacitor the current reaches its maximum before the voltage does, so the current leads the voltage by a quarter cycle, which is 90 degrees. This is the opposite of an inductor, where the current lags.

Question 8Fundamentals of Electricity and Magnetism

A coil of 200 turns is linked by a magnetic flux that changes from 0.02 Wb to 0.06 Wb in 0.5 s. What is the average emf induced in the coil?

  1. 32 V
  2. 8 V
  3. 4 V
  4. 16 V Correct answer.

Explanation

The change in flux is 0.04 Wb over 0.5 s, giving a rate of 0.08 Wb/s per turn. Multiplying by 200 turns gives 16 V as the average induced emf.

Question 9Fundamentals of Electricity and Magnetism

A parallel-plate capacitor has a capacitance of 10 μF and is charged to 100 V. How much energy is stored in it?

  1. 1 J
  2. 5 J
  3. 0.5 J
  4. 0.05 J Correct answer.

Explanation

The energy stored in a capacitor is given by W = ½CV², so W = 0.5 × 10 × 10⁻⁶ × 100² = 0.05 J. The factor of one half arises because the voltage rises from zero to its final value during charging.

Question 10Fundamentals of Electricity and Magnetism

In a series RLC circuit operating at resonance, which statement about the circuit is correct?

  1. The impedance is maximum and equals the reactance
  2. The current is minimum
  3. The impedance is minimum and equals the resistance Correct answer.
  4. The power factor is zero

Explanation

At resonance the inductive and capacitive reactances are equal and cancel, so the impedance falls to the value of the resistance alone. The current is then maximum and the power factor is unity.

Question 11Fundamentals of Electricity and Magnetism

A moving-coil ammeter is used to measure an alternating current. What reading does it give?

  1. The peak value of the current
  2. The rms value of the current Correct answer.
  3. The average value of the current over a cycle
  4. The instantaneous value at that moment

Explanation

A moving-coil instrument responds to the average torque, and on AC this produces a reading proportional to the rms value when calibrated for AC. Its deflection is proportional to the mean square of the current, so it indicates the effective or rms value.

Question 12Fundamentals of Electricity and Magnetism

A conductor of length 0.5 m carrying a current of 4 A is placed at right angles to a uniform magnetic field of flux density 0.2 T. What is the force on the conductor?

  1. 0.4 N Correct answer.
  2. 0.04 N
  3. 0.8 N
  4. 4 N

Explanation

The force on a current-carrying conductor in a magnetic field is F = BIL sin θ, and here θ is 90 degrees, so sin θ = 1. Thus F = 0.2 × 4 × 0.5 = 0.4 N.

Question 13Fundamentals of Electricity and Magnetism

What is the function of a commutator in a DC generator?

  1. It increases the magnetic flux in the field winding
  2. It reduces the speed of the prime mover
  3. It converts the alternating emf in the armature coil into a unidirectional emf in the external circuit Correct answer.
  4. It stores energy for later use

Explanation

The commutator acts as a mechanical rectifier that reverses the connections of the armature coil at the instant the emf reverses. This keeps the output to the external circuit unidirectional, which is the defining feature of a DC generator.

Question 14Fundamentals of Electricity and Magnetism

Two capacitors of 4 μF and 6 μF are connected in series across a 100 V supply. What is the charge on each capacitor?

  1. 600 μC
  2. 1000 μC
  3. 400 μC
  4. 240 μC Correct answer.

Explanation

In series the equivalent capacitance is (4 × 6)/(4 + 6) = 2.4 μF, and the charge on each capacitor is the same, Q = CV = 2.4 μF × 100 V = 240 μC.

Question 15Fundamentals of Electricity and Magnetism

Why is laminated construction used for the core of a transformer?

  1. To reduce eddy current losses Correct answer.
  2. To improve the mechanical strength of the windings
  3. To increase the hysteresis loss
  4. To increase the weight of the core

Explanation

Laminations are thin sheets insulated from each other, which break up the paths available for circulating eddy currents. This greatly reduces eddy current loss and heating in the core.

Question 16Fundamentals of Electricity and Magnetism

A 3-phase induction motor has a synchronous speed of 1500 rpm and a full-load speed of 1440 rpm. What is the percentage slip?

  1. 2.5 percent
  2. 96 percent
  3. 6 percent
  4. 4 percent Correct answer.

Explanation

Slip is calculated as (Ns − N)/Ns × 100, so (1500 − 1440)/1500 × 100 gives 4 percent. Slip is always a small percentage at normal running speeds.

Question 17Fundamentals of Electricity and Magnetism

What is the effect of increasing the number of poles on the synchronous speed of an induction motor for a given supply frequency?

  1. The synchronous speed becomes zero
  2. The synchronous speed remains unchanged
  3. The synchronous speed increases
  4. The synchronous speed decreases Correct answer.

Explanation

Synchronous speed is given by Ns = 120f/P, so for a fixed frequency an increase in the number of poles P reduces the synchronous speed. This is why low-speed machines are built with many poles.

Question 18Fundamentals of Electricity and Magnetism

A current of 5 A flows through a resistor of 40 Ω for 2 minutes. What is the heat produced?

  1. 400 J
  2. 24000 J
  3. 120000 J Correct answer.
  4. 2000 J

Explanation

Joule's law gives heat H = I²Rt, so H = 5² × 40 × 120 = 120000 J. The time must be converted to seconds before substitution.

Question 19Fundamentals of Electricity and Magnetism

A coil of resistance 8 Ω and inductive reactance 6 Ω is connected to an AC supply. What is its impedance?

  1. 10 Ω Correct answer.
  2. 14 Ω
  3. 48 Ω
  4. 2 Ω

Explanation

Impedance in an RL circuit is given by Z = √(R² + X²), so Z = √(64 + 36) = √100 = 10 Ω. Resistance and reactance add vectorially, not arithmetically.

Question 20Fundamentals of Electricity and Magnetism

A magnetic circuit has a flux density of 0.8 T in a core of cross-sectional area 0.005 m². What is the total flux in the core?

  1. 0.16 Wb
  2. 0.0004 Wb
  3. 0.004 Wb Correct answer.
  4. 0.04 Wb

Explanation

Magnetic flux is flux density multiplied by the area perpendicular to it, so Φ = B × A = 0.8 × 0.005 = 0.004 Wb. Flux density is therefore flux per unit area.

Question 21Fundamentals of Electricity and Magnetism

A coil of 500 turns is wound on a magnetic circuit. When the current changes at 2 A/s, the self-induced emf is 10 V. What is the inductance of the coil?

  1. 2.5 H
  2. 0.2 H
  3. 5 H Correct answer.
  4. 1000 H

Explanation

From e = L(di/dt), the inductance equals e divided by the rate of change of current, so L = 10/2 = 5 H. The number of turns is already reflected in the measured emf.

Question 22Fundamentals of Electricity and Magnetism

A transformer has 400 primary turns and 40 secondary turns. If the primary is connected to a 220 V AC supply, what is the secondary voltage under no load?

  1. 110 V
  2. 22 V Correct answer.
  3. 44 V
  4. 2200 V

Explanation

For an ideal transformer the voltage ratio equals the turns ratio, so V₂ = V₁ × (N₂/N₁) = 220 × 40/400 = 22 V. This is a step-down transformer because the secondary turns are fewer.

Question 23Fundamentals of Electricity and Magnetism

A capacitor of 50 μF is connected across a 200 V, 50 Hz supply. What is the capacitive reactance?

  1. 31.8 Ω
  2. 63.7 Ω Correct answer.
  3. 100 Ω
  4. 15.9 Ω

Explanation

Capacitive reactance is Xc = 1/(2πfC), so Xc = 1/(2π × 50 × 50 × 10⁻⁶) which is approximately 63.7 Ω. Reactance falls as either frequency or capacitance is increased.

Question 24Fundamentals of Electricity and Magnetism

Two parallel conductors carry currents in opposite directions. What is the nature of the force between them?

  1. They attract each other
  2. They experience a twisting torque only
  3. No force acts between them
  4. They repel each other Correct answer.

Explanation

Each conductor sets up a magnetic field that acts on the other, and when the currents flow in opposite directions the resulting forces push the conductors apart. Conductors carrying current in the same direction attract each other.

Question 25Wiring Systems, Cables and Accessories

In a domestic single-phase installation wired in PVC conduit, which conductor colour is conventionally used for the earth continuity conductor when the wiring is done as per IS 732 practice?

  1. Blue
  2. Black
  3. Red
  4. Green with yellow stripe Correct answer.

Explanation

Indian practice reserves green or green-with-yellow-stripe for the protective earth conductor so that anyone opening an accessory immediately identifies the safety conductor. Phase and neutral use other colours, and the earth conductor must never be used to carry load current.

Question 26Wiring Systems, Cables and Accessories

A 1.5 sq mm copper conductor of a lighting sub-circuit is protected by a 6 A MCB. Which property of the cable primarily justifies that the MCB rating is chosen below the cable current rating?

  1. Current-carrying capacity of the cable Correct answer.
  2. Mechanical strength of the conductor
  3. Voltage drop along the run
  4. Insulation resistance of the cable

Explanation

Coordination requires the protective device rating to be not greater than the cable current-carrying capacity, so the cable is not overheated before the device trips. Voltage drop affects performance but does not protect the insulation from thermal damage.

Question 27Wiring Systems, Cables and Accessories

While fixing a batten holder on a wooden ceiling board, which accessory is used to give a firm seating and to keep the base clear of the board surface?

  1. Wooden batten Correct answer.
  2. PVC casing
  3. Ceiling rose
  4. Brass hook

Explanation

A wooden batten is screwed to the ceiling and the holder is mounted on it, giving a firm base and keeping the wiring entry clear. Ceiling roses and hooks serve different purposes in the lighting circuit.

Question 28Wiring Systems, Cables and Accessories

A two-way lighting circuit is required so that a lamp can be switched from either end of a corridor. Which switch is essential at each end?

  1. Intermediate switch
  2. Push-button bell switch
  3. Two-way switch Correct answer.
  4. One-way switch

Explanation

A two-way switch has one common terminal and two strapper terminals, allowing the live feed to be diverted through either strap. Two such switches at the ends of the corridor give control from both positions.

Question 29Wiring Systems, Cables and Accessories

In a three-way lighting arrangement using two two-way switches and one intermediate switch, how many conductors run between the intermediate switch and each two-way switch?

  1. Four
  2. Two Correct answer.
  3. Three
  4. One

Explanation

The intermediate switch has two incoming and two outgoing strapper terminals, so two conductors connect it to each two-way switch. The switching action simply cross-connects the incoming pair to the outgoing pair.

Question 30Wiring Systems, Cables and Accessories

A surface wiring run in a workshop must be protected against mechanical damage where it crosses a doorway at low height. Which accessory is most suitable at that crossing?

  1. A steel conduit saddle
  2. A junction box
  3. A flexible conduit length
  4. Casing and capping Correct answer.

Explanation

Casing and capping encloses the conductors in a rigid channel that resists impact and is commonly used for surface runs in workshops. Saddles and junction boxes perform supporting and connection duties rather than mechanical protection along a run.

Question 31Wiring Systems, Cables and Accessories

Which wiring system is preferred in a chemical plant where corrosive vapours are present and the installation must be mechanically robust?

  1. Steel conduit wiring Correct answer.
  2. PVC casing and capping
  3. Concealed PVC conduit
  4. Cleat wiring

Explanation

Steel conduit gives mechanical strength and, when galvanised, reasonable resistance to corrosive atmospheres, so it is chosen for industrial and chemical environments. Cleat and casing systems expose the cable and offer little protection.

Question 32Wiring Systems, Cables and Accessories

A rigid steel conduit run is being installed between two inspection bends. What is the main reason for limiting the number of bends between draw boxes?

  1. To increase the current rating of the cable
  2. To reduce the cost of conduit
  3. To make cable pulling possible without excessive stress Correct answer.
  4. To improve the earth continuity of the conduit

Explanation

Each bend adds friction, so too many bends between draw points make pulling difficult and can damage the insulation. Inspection or draw boxes are inserted to keep each pull short and smooth.

Question 33Wiring Systems, Cables and Accessories

A conduit installation is to be tested for earth continuity. Which condition should the test confirm?

  1. That the conduit has zero voltage drop
  2. That the conduit is insulated from all metalwork
  3. That the conduit provides a low-resistance path to earth Correct answer.
  4. That the conduit carries the full load current

Explanation

Metal conduit is used as a protective conductor in many installations, so the test verifies a low-resistance path from the farthest point back to the earth terminal. The conduit must never be relied on to carry load current.

Question 34Wiring Systems, Cables and Accessories

Which test instrument is used to measure the insulation resistance of a wiring installation before it is energised?

  1. Multimeter on the DC volts range
  2. Earth tester
  3. Megger Correct answer.
  4. Clamp meter

Explanation

A megger applies a high DC test voltage and reads insulation resistance in megohms, which is the standard pre-energisation check. A clamp meter and earth tester measure current and earth electrode resistance respectively.

Question 35Wiring Systems, Cables and Accessories

A PVC-insulated cable is to be selected for a circuit where the ambient temperature is higher than the standard reference. What effect does the higher ambient temperature have on the cable current rating?

  1. The rating remains unchanged
  2. The rating increases in proportion to temperature
  3. The rating decreases Correct answer.
  4. The rating becomes independent of conductor size

Explanation

Higher ambient temperature reduces the permissible temperature rise for a given current, so the current-carrying capacity must be derated. This is why correction factors are applied when cables run in hot locations.

Question 36Wiring Systems, Cables and Accessories

Which of these is the correct purpose of a cable gland at the entry of a cable into a metal enclosure?

  1. To reduce the voltage drop along the cable
  2. To provide a junction for branch circuits
  3. To secure the cable and maintain earth continuity to the enclosure Correct answer.
  4. To increase the current rating of the cable

Explanation

A cable gland mechanically anchors the cable and, in the case of armoured cable, bonds the armour to the enclosure for earth continuity. This is essential for safety and for a sound installation.

Question 37Wiring Systems, Cables and Accessories

A single-core armoured cable is to be terminated in a switchgear panel. Why is the armour of a single-core cable usually not used as the sole earth path?

  1. The armour cannot be bonded to the panel
  2. The armour is made of insulating material
  3. The armour carries circulating currents induced by the alternating field Correct answer.
  4. The armour has no mechanical strength

Explanation

In single-core cables the alternating flux links the armour and induces circulating currents, causing heating; hence a separate earth conductor is used with suitable bonding arrangements. The armour still provides mechanical protection.

Question 38Wiring Systems, Cables and Accessories

Which accessory is used to join two lengths of conduit in a straight run while allowing the joint to be opened for drawing cables?

  1. Inspection tee
  2. Coupler Correct answer.
  3. Elbow
  4. Bend

Explanation

A coupler is a straight socket that joins two conduit lengths in line. Bends and elbows change direction, while an inspection tee provides a branch and an opening for access.

Question 39Wiring Systems, Cables and Accessories

In a concealed conduit installation, why is the conduit laid before plastering and the cable drawn in afterwards?

  1. To allow replacement of the cable without breaking the wall Correct answer.
  2. To avoid the need for an earth conductor
  3. To increase the current rating of the cable
  4. To reduce the cost of the cable

Explanation

Drawing the cable in after the conduit is embedded means the wiring can be replaced or rewired later without disturbing the plaster or masonry. This is a key advantage of the concealed conduit system.

Question 40Wiring Systems, Cables and Accessories

A socket outlet in a bathroom is to be installed. Which measure best reduces the risk of electric shock in this location?

  1. Increasing the socket current rating to 16 A
  2. Using a longer flexible cord
  3. Providing additional protection by a residual current device Correct answer.
  4. Connecting the socket directly to the phase without an earth

Explanation

A residual current device detects small earth-leakage currents and disconnects the supply quickly, giving additional protection in wet locations. The earth connection must always be maintained and never omitted.

Question 41Wiring Systems, Cables and Accessories

Which type of wiring is most suitable for temporary installations such as a fairground stall that is dismantled after a few days?

  1. Flexible cable with suitable plugs and sockets Correct answer.
  2. Cleat wiring
  3. Concealed conduit wiring
  4. Underground cable laid in a trench

Explanation

Temporary installations need quick assembly and dismantling, so flexible cable with proper plugs and sockets is appropriate. Concealed and underground systems are permanent and cannot be removed easily.

Question 42Wiring Systems, Cables and Accessories

What is the standard purpose of a ceiling rose in a domestic lighting circuit?

  1. To switch the lamp on and off
  2. To step down the supply voltage to the lamp
  3. To protect the lamp from overcurrent
  4. To provide a connection point between the circuit wiring and the pendant flex Correct answer.

Explanation

A ceiling rose houses the terminal block where the fixed circuit conductors connect to the flexible pendant cord. It does not transform voltage, protect against overcurrent, or perform switching.

Question 43Wiring Systems, Cables and Accessories

A flexible cord is to be connected to a portable appliance. Which conductor of the cord is connected to the metal body of the appliance?

  1. The phase conductor
  2. Any of the three conductors
  3. The protective earth conductor Correct answer.
  4. The neutral conductor

Explanation

The protective earth conductor is connected to the exposed metalwork so that a fault current flows to earth and operates the protective device. Connecting phase or neutral to the body would create a serious shock hazard.

Question 44Wiring Systems, Cables and Accessories

A conduit run in a masonry wall has to pass through a wall at an angle. Which fitting allows the direction to be changed while still permitting cables to be drawn?

  1. Coupler
  2. Solid bend
  3. Inspection bend Correct answer.
  4. Locknut

Explanation

An inspection bend has a removable cover so cables can be guided and drawn through the change of direction. A solid bend would make drawing difficult, and a coupler or locknut performs a different function.

Question 45Wiring Systems, Cables and Accessories

Why is it important to maintain a minimum bending radius when installing a PVC-insulated cable?

  1. To reduce the number of cable supports required
  2. To keep the cable straight for appearance
  3. To prevent damage to the insulation and conductor Correct answer.
  4. To increase the current rating of the cable

Explanation

Sharp bends stress the insulation and can crack it or damage the conductor strands, leading to premature failure. The manufacturer's minimum bending radius must be respected during installation.

Question 46Wiring Systems, Cables and Accessories

A distribution board is fed by a cable whose fault level is high. Which property of the protective device must be checked to ensure it can safely interrupt the prospective fault current?

  1. Voltage drop
  2. Insulation resistance
  3. Earth loop impedance
  4. Breaking capacity Correct answer.

Explanation

The breaking capacity must exceed the prospective short-circuit current at the point of installation so the device can clear the fault without damage. Voltage drop and insulation resistance are unrelated to fault interruption.

Question 47Wiring Systems, Cables and Accessories

Which of the following is the correct sequence when preparing a PVC conduit end for termination at a switch box?

  1. Cut the conduit, fit a coupler, then fix the box
  2. Cut the conduit, fit a bush, then thread the conduit into the box
  3. Cut the conduit, bend it, then fit a locknut
  4. Cut the conduit, thread it, fit a locknut and bush, then fix the box Correct answer.

Explanation

The conduit is cut square, threaded if a threaded entry is used, and secured to the box with a locknut on the outside and a bush on the inside to protect the cable. This gives a sound mechanical and protective termination.

Question 48Wiring Systems, Cables and Accessories

A wiring installation shows an insulation resistance of 0.4 megohm between phase and neutral. What does this indicate?

  1. The circuit has a short circuit and will trip immediately
  2. The insulation resistance is below the acceptable minimum and the cause must be investigated Correct answer.
  3. The insulation is healthy and the circuit may be energised
  4. The earth continuity is satisfactory

Explanation

Insulation resistance well below the usual minimum of about one megohm indicates moisture, damage, or contamination, and the circuit must not be energised until the fault is found and corrected. A dead short would read close to zero, not 0.4 megohm.

Question 49Electrical Machines: Transformers, Induction and DC Motors

A 50 Hz single-phase transformer has a turns ratio of 10:1. If the primary voltage is 230 V, what is the approximate secondary voltage on no load?

  1. 2300 V
  2. 115 V
  3. 23 V Correct answer.
  4. 230 V

Explanation

For an ideal transformer the voltage ratio equals the turns ratio, so secondary voltage is primary voltage divided by the ratio: 230/10 = 23 V. This holds on no load, where the small magnetising current causes negligible drop.

Question 50Electrical Machines: Transformers, Induction and DC Motors

In a transformer, the core is laminated primarily to reduce which loss?

  1. Eddy current loss Correct answer.
  2. Friction and windage loss
  3. Copper loss
  4. Hysteresis loss

Explanation

Laminations interrupt the paths of induced eddy currents in the core, raising the resistance of those paths and cutting I-squared-R eddy loss. Hysteresis loss depends on the core material and frequency, not on lamination thickness.