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Past Questions
In house wiring employing looping in and looping out system, phase Wire is looped in and looped out from:
A)
Socket
B)
ceiling rose
C)
lamp holder
D)
switch
In looping-in and looping-out wiring, the phase (live) wire is taken to the switch first and then looped onward to other points. The switch is therefore the point from which the phase wire is looped in and looped out. A ceiling rose or lamp holder is connected after the switch, while the socket is not the usual looping point for the phase wire in this context.
Which is better earth resistance:
A)
1 ohm
B)
50 ohm
C)
100 ohm
D)
0.5 ohm
Lower earth resistance is better because it allows fault current to flow safely to ground and improves protection. Among the given values, 0.5 ohm is the lowest, so it is the best earth resistance. 1 ohm is also good, but higher than 0.5 ohm. 50 ohm and 100 ohm are too high for effective earthing.
The speed of AC motor depends on:
A)
Frequency
B)
Number of poles
C)
Both (a) & (b)
D)
none of them
The speed of an AC motor, especially an induction or synchronous motor, depends on the supply frequency and the number of poles. The synchronous speed is given by Ns = 120f / P, where f is frequency and P is number of poles. Hence, both frequency and number of poles affect the motor speed. Option (a) alone is incomplete, option (b) alone is also incomplete, and (d) is incorrect.
Efficiency of a power transformer is of the order of:
A)
75%
B)
50%
C)
98%
D)
100%
A power transformer is designed for very high efficiency, typically around 98% to 99% or even slightly higher at rated load, because its copper and core losses are very small compared with its power rating. 75% and 50% are far too low for a power transformer, while 100% is impossible in practice due to unavoidable losses.
Refrigeration and air -conditioning involve heat transfer using:
A)
water
B)
ice and water
C)
refrigerants
D)
none of above
Refrigeration and air-conditioning systems transfer heat by circulating a working fluid called a refrigerant. The refrigerant absorbs heat at low temperature and pressure and rejects it at higher temperature and pressure. Water or ice-water may be used in some cooling applications, but the basic heat-transfer medium in refrigeration and air-conditioning is the refrigerant.
Iron core of power transformer is laminated:
A)
to reduce copper losses
B)
to reduce hysteresis losses
C)
to reduce eddy current losses
D)
due to (b) and (c)
The iron core of a power transformer is laminated to break up the path of circulating currents induced in the core by alternating magnetic flux. These circulating currents are called eddy currents, and lamination increases the resistance to their flow, thereby reducing eddy current loss. Copper loss occurs in the windings, not in the iron core, so (a) is incorrect. Hysteresis loss depends on the magnetic properties of the core material, not on lamination, so (b) is incorrect. Since only eddy current loss is reduced by lamination, (d) is also incorrect.
The main function of power transformer is:
A)
to increase or decrease the d.c. voltage
B)
to increase or decrease the a.c. voltage
C)
to convert a.c. to d.c. vice-versa
D)
none of all
A transformer works on the principle of mutual induction and operates only with alternating current. Its main function is to step up or step down AC voltage in power systems. It cannot change DC voltage directly, and it does not convert AC to DC or vice versa. Therefore, option (b) is correct.
Two-way single pole switch controls:
A)
Connection of two wires to two positions
B)
connection of one wire to two positions
C)
connection of one wire to one position
D)
connection of two wire to four position
A two-way single pole switch is used to control one load from two different locations. It has two possible positions and connects the common terminal to one of two traveler wires. Hence, it controls the connection of two wires to two positions. Option (b) describes a one-way switch concept, while (c) and (d) do not correctly describe a two-way single pole switch.
Megger is used to measure:
A)
Breakdown voltage of insulation
B)
insulation resistance
C)
earth resistance
D)
none of above
A megger (megohmmeter) is used to measure the insulation resistance of electrical cables, motors, and wiring. It applies a high DC test voltage and indicates resistance in megaohms. It is not primarily used to measure breakdown voltage, and earth resistance is measured by an earth tester, not a megger.
The standard single phase AC supply voltage in India is:
A)
110V
B)
415V
C)
230V
D)
none of above
The standard single-phase AC supply voltage in India is 230 V. Option (b) 415 V is the standard three-phase line voltage, not single-phase. Option (a) 110 V is used in some countries, not India. Therefore, the correct answer is (c) 230V.
1(one) Ton of refrigeration is equal to:
A)
15,000 BTU/hr
B)
13,000 BTU/hr
C)
12,000 BTU/hr
D)
none of above
1 ton of refrigeration (1 TR) is defined as the rate of heat removal required to freeze 1 ton of water at 0°C into ice in 24 hours. Its standard equivalent is 3.517 kW, which is approximately 12,000 BTU per hour. Therefore, option (c) is correct. Options (a) and (b) are higher than the standard value, and (d) is incorrect.
Fans and lamps in domestic installation are connected in:
A)
series and parallel combination
B)
series
C)
parallel
D)
none of above
In domestic wiring, fans and lamps are connected in parallel so that each appliance gets the full supply voltage and can be operated independently. If one lamp or fan fails, the others keep working. In series connection, the voltage would be divided and all devices would be affected together, so that is not used for house wiring.
Sparking occurs when a load is switched off because the circuit has:
A)
high inductance
B)
high impedance
C)
high resistance
D)
high Capacitance
When a load containing inductance is switched off, the current through the inductor cannot change abruptly. The collapsing magnetic field produces a large back EMF, which can cause sparking at the switch contacts. Hence sparking occurs due to high inductance. High resistance or high impedance would reduce current, and capacitance is not the main cause here.
1(one) horse-power is equal to:
A)
546 W
B)
656 W
C)
746 W
D)
none of above
1 horse-power (HP) is a standard unit of power and is approximately equal to 746 watts. Therefore, option (c) is correct. Option (a) 546 W is incorrect because 546 W is not the standard conversion for 1 HP. Option (b) 656 W is also incorrect. Hence, the correct answer is 746 W.
Suppliers fuse which is sealed is provided:
A)
before the energy meter
B)
after the main switch
C)
before distribution board
D)
after the energy meter
A supplier’s fuse (service fuse) is installed on the supply side, i.e., before the energy meter. It protects the incoming service line and the consumer’s installation from overcurrent. The energy meter should be protected by the supplier’s fuse, so it is not placed after the meter. Hence, option (a) is correct.
In a.c. circuit, fuse is inserted only in:
A)
Earth wire
B)
neutral wire
C)
live wire
D)
none of above
In an a.c. circuit, the fuse is connected in the live wire so that when excessive current flows, it breaks the supply to the appliance completely. If it were placed in the neutral wire, the appliance could still remain connected to the live potential, which is unsafe. Hence, the correct answer is live wire.
The main function of power transformer is:
A)
to increase or decrease the d.c. voltage
B)
to increase or decrease the a.c. voltage
C)
to convert a.c. to d.c. vice-versa
D)
none of all
A transformer works only on alternating current (AC) because it operates on the principle of mutual induction. Its main function is to step up or step down AC voltage. It cannot directly change DC voltage, and it does not convert AC to DC or vice-versa. Therefore, option (b) is correct.
The number of power points allowed on 1(one) circuit in house wiring is:
A)
1 point of 500 watts
B)
2 points of 1000/2000 watts each
C)
3points of 500 watts each
D)
none of the above
In house wiring, a power circuit is generally restricted to a single power point with a load of about 500 W. This is to prevent overloading and to keep the wiring within safe current-carrying limits. Options (b) and (c) exceed the usual permissible load for one circuit, so they are incorrect. Hence, the correct answer is (a) 1 point of 500 watts.
If a piece of metal wire is stretched, its resistance will increase:
A)
True
B)
False
C)
Both (a) and (b) are true
D)
Both (a) and (b) are false
When a metal wire is stretched, its length increases and its cross-sectional area decreases. Since resistance is given by R = ρL/A, both changes cause the resistance to increase. Therefore, the statement is true. Option (b) is incorrect because stretching does not decrease resistance. Options (c) and (d) are incorrect because they combine contradictory statements.
In two W meter method, if the power factor is unity, then:
A)
W1 > W2
B)
W1 < W2
C)
W1 = W2
D)
none of above
In the two-wattmeter method, the power factor angle is given by tan φ = √3 (W1 − W2) / (W1 + W2). If the power factor is unity, then φ = 0°, so tan φ = 0. This means W1 − W2 = 0, hence W1 = W2. Therefore, both wattmeters read the same value. Options (a) and (b) are incorrect because there is no difference between the readings at unity power factor.
Continuity of an electrical circuit is usually checked by:
A)
Ammeter
B)
voltmeter
C)
ohm meter
D)
all of above
Continuity of a circuit means checking whether the path is complete and has very low resistance. An ohmmeter is used to measure resistance, so it can verify continuity. An ammeter measures current, and a voltmeter measures voltage, so they are not the usual instruments for continuity testing. Therefore, the correct answer is ohm meter.
The electric motor helps the elevator car to:
A)
move downward
B)
move upward
C)
both (a) and (b)
D)
none of these
In an elevator, the electric motor drives the traction system so the car can move in both directions. It helps lift the car upward and, through controlled braking and counterweight action, also allows downward movement. Therefore, the correct answer is both upward and downward movement.
The S.I. Unit of luminous flux is:
A)
Lux
B)
lumen
C)
candela
D)
none of above
Luminous flux is the total quantity of light energy emitted per second, and its SI unit is the lumen. Lux is the unit of illumination (luminous flux per unit area), and candela is the SI unit of luminous intensity. Therefore, the correct answer is lumen.
The effect on resistance of good conductor is:
A)
Resistance decrease
B)
resistance remain the same
C)
resistance increases
D)
none of them
For a good conductor, as temperature increases, lattice vibrations increase and electrons face more collisions. This makes the resistance increase. Hence option (c) is correct. Option (a) is wrong because resistance does not decrease in a good conductor with rise in temperature. Option (b) is wrong because resistance is not constant. Option (d) is incorrect because one of the given options is correct.
Type of lift that is used in offices is:
A)
passenger lift
B)
hospital lift
C)
car lift
D)
Goods lift
An office building primarily requires a lift meant for carrying people, so the correct type is a passenger lift. Hospital lifts are designed for stretchers and medical use, car lifts are for vehicles, and goods lifts are meant for transporting materials rather than office occupants.