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Browse complete papersA room requires an average illuminance of 200 lux over a 60 square meter area. If the total luminous flux emitted by the lamps is 15000 lumens and the utilization factor is 0.8, what is the actual illuminance achieved?
100 lux
200 lux
160 lux
125 lux
Correct answer
100 lux
What happens to the magnetic field around a straight current-carrying conductor when the current through it is increased?
Magnetic field strength increases
Magnetic field strength decreases
Magnetic field strength remains the same
Magnetic field disappears
Correct answer
Magnetic field strength increases
In a series R-C circuit supplied with sinusoidal AC voltage, the current leads the applied voltage by an angle Ø. Which of the following correctly expresses this phase angle?
tan Ø = \(\frac{R}{X_C} \)
tan Ø = XCR
tan Ø = \(-\frac{X_C}{R}\)
tan Ø = \( - \frac{R}{X_C} \)
Correct answer
tan Ø = \(\frac{R}{X_C} \)
The maximum fault current attained during a short circuit at the instant before the fuse completely interrupts the circuit is called:
Cut-off current
Rated current
Melting current
Breaking capacity
Correct answer
Cut-off current
Megger is an instrument used to measure ______.
Current carrier.
Source of e.m.f.
High resistance.
Type of a null detector.
Correct answer
Current carrier.
Which of the following is a key maintenance practice for reliable operation of a 3-phase induction motor?
Regular lubrication of bearings and periodic insulation resistance testing.
Increasing slip by intentionally weakening rotor bars.
Short-circuiting the stator windings when the motor is idle.
Running the motor continuously at no-load to avoid heating.
Correct answer
Regular lubrication of bearings and periodic insulation resistance testing.
On a CRO screen, a DC voltage causes a vertical deflection of 4 divisions. If the vertical sensitivity is 2 V/div, what is the value of the DC voltage?
4 V
8 V
6 V
2 V
Correct answer
4 V
Which of the following statements about damping in moving-iron instruments is correct?
Damping in MI instruments is usually provided by a permanent magnet
Damping in MI instruments is usually provided by air friction
Damping in MI instruments is usually provided by eddy currents in an aluminium disc
Damping in MI instruments is usually not required because the pointer is very light
Correct answer
Damping in MI instruments is usually provided by a permanent magnet
In a three-phase induction energy meter, the disc rotates due to the interaction between the magnetic fields produced by:
the shunt coil and the field winding
the pressure and current coils
the mechanical gears and shaft
the current and cooling coils
Correct answer
the shunt coil and the field winding
An induction furnace operates at 10 kHz and is used to melt 100 kg of steel. If the efficiency is 60% and the energy required to melt steel is 1500 kWh/ton, what is the minimum energy input needed?
150 kWh
90 kWh
250 kWh
180 kWh
Correct answer
150 kWh