|1 Crore+ students have signed up on EduRev. Have you?|
A cube of material of side 1 cm has a resistance of 0.002W between its opposite faces. If the same volume of the material has a length of 8 cm and a uniform cross-section the resistanceof this length will be
The incandescent bulb rated respectively as P1 and P2 for operation at a specified main voltage are connected in series across the mains as shown in the figure. Then the total power supplied by the mains to the two bulbs.
A metal filament lamp X rated 40 W, 100 V is connected in series with another lamp Y of the same type rated 100W, 200V. A voltage of 200V is applied across the combination then
A 100W, 200V, filament lamp has operating temperature of 2000ºC. The filament materialhas resistance temperature coefficient of 0.005 at OºC per ºC. The current taken by the lamp at the instant of switching with 200V supply with filament temperature of 20ºC will be
The equivalent resistance at 'the points X1 and X2 in the circuits shown below
In the circuit shown in the given figure. The current through the inductor L is
A series RLC circuit is switched ON to a step voltage 'V' at t=0. What are initial and finalvalues of the current in the circuit respectively?
(1) Under steady state condition, a pure inductor act as a short circuit for direct current
(2) The potential drop across an inductance is proportional to the rate of change of current
According to maximum power transfer theorem, when is the maximum power absorbed by onenetwork from another network ?
At resonant frequency a R-L-C series circuit draws maximum current due to the reason that
If for sinusoids of same frequency but ofdifferent amplitudes and phase difference areadded the resultant is a
A pure capacitance connected across 50Hz, 230V supply consumes 0.04W. This consumption is attributed to
A 2-terminal network consist of one of the RLC elements. The element is connected to an ac supply. The current through the element is IA when an inductor is inserted in series between the source and element 2IA the current through the element becomes. What is this element ?
With the increase in applied frequency, thedielectric loss in a material will
A 100W, 100V bulb is to be supplied from 220V, 50Hz supply. Which of the following arrangement is preferable ?
A small capacitance is added to a highly inductive circuit
Capacitive susceptance is a measure of
Q-factor of a series R-L-C circuit possessing resonant frequency of 10Hz and bandwidth of 5Hz is
A parallel circuit is said to be in resonance when the admittance is purely
A conductor of length 100 cm moves at right angle to a uniform field flux density of 1.5 W6/m2 with a velocity of 50 m/s. The emf induced in the conductor will be
Magnetic materials which may be readily magnetized in either direction are
The relative permeability is less than unity in case of
A 1000 turn solenoid develops an average induced voltage of 120 volts. Over what timeinterval must a flux change of 60 milli-webers occurs to produce such a voltage ?
A long solenoid with 2000 turns is 0.8 m long. What is the magnetising force in the centre of this solenoid, if the exciting current is 2A
For a D.C. machine laboratory following type of DC supply will be used
Lamination of core are generally made of
The speed control of dc shunt motor in both directions can be obtained by
A synchronous motor operates at rated voltageand rated frequency and has a load torque angle of 30º. If both the terminal voltage & frequency are reduced by 10%, then
The nature of armature mmf for a zero power factor lagging load in a 3-f alternator is
Correct Answer :- B
Explanation : The effect of armature reaction mmf is purely demagnetizing in zero pf lagging load condition. This can be explained in 2 methods :
In Zero power factor lagging load, the load current is lagging behind the excitation voltage by 90 degree.
Due to zero power factor lagging load, the current in phase “a” of armature winding will become maximum when the field poles have advanced by 90 degree in assumed counter-clockwise direction.
The frequency of rotor emf of an 8-pole induction motor is 24HZ. If the supply frequency is 50Hz, then the motor speed is
Correct Answer : D
Number of poles (P) = 8
Frequency (f) = 50
N₁ = 120x50 = 750 rpm
Frequency of rotor emf = sf = 2 Hz
Supply frequency = f = 50 Hz
⇒ s = 0.04
Rotor speed = Ns (1 s) = 750 (1-0.04) = 720 rpm
For a given applied voltage and current, the speed of a universal motor will be
Which of the following is the main advantage of an auto-transformer over a two winding transformer ?
When a given transformer is run at a its rated voltage but reduced frequency its
A 2000/200V, 50 Hz single phase transformer has an exciting current of 0.5A and a core loss of 600W. When H.V. side is energized by the rated voltage and frequency, the magnetisingcurrent is
In case of dc motor, maximum mechanical power is developed, when back emf equals
If Pc & Psc represent core & full-load ohmic losses respectively, the maximum KVAdelivered to load corresponding to maximum efficiency is equal to rated KVA multiplied by
Under no load conditions, which of the following loss is negligible ?
Open circuit test of a transformer gives
Which test on transformer provides information about regulation, efficiency and heading under load conditions ?
If flux density in the core of a transformer is increased
The driving power from the prime mover driving the alternator is lost but the alternator remainsconnected to the supply network and the field supply also remains on. The alternator will
Two alternators are running in parallel. If the driving force of both the alternators is changed this will result in change is
The armature reaction of an alternator influences
In an alternator if the armature reaction produces magnetisation of the main field the power factor should be
Correct Answer :- a
Explanation : Zero Power factor means that either the circuit is purely resistive or purely capacitive.
If the load is purely capacitive or at the leading power factor, the effect of armature reaction is of magnetizing type.
Note:- In the magnetizing effect, armature flux assists main field flux hence greater EMF is induced in the armature. Hence there is an increase in the terminal voltage for leading power factor loads
As the load on an induction motor increases
A 3-f 420V, 60Hz induction motor is to be run on 50 Hz supply. Which of the following will be the satisfactory supply voltage for the machine ?
The torque of a reluctance motor can be effectively increased by
A 2-phase servomotor in control system uses
In dc machines, the field flux axis and the armature mmf axis are respectively along
A power station has a maximum demand of 2500 kw and number of kwh generated per year is 45×105. The load factor is
A long overhead losses power transmission line is terminated with its characteristic impedance while the line is in operation
In case of single line to ground fault
Which of the following circuit breakers has the lowest voltage range ?
Which of the following will be provided to reduce the harmonics on the a.c. side of an HVDC transmission line ?
Which distribution system is more reliable ?
Which of the following circuit breakers does not use pneumatic operating mechanism
A relay used for protection of motors against overload is
Switching over-voltages are more hazardous than lightening surges in case of
Series reactors are installed at strategic locations of power systems to
Single core cables are usually not provided with
Copper as conductors for cables is used as
If two synchronous generators are connected loss of synchronism will result in
The maximum demand of a power station is
Static capacitor are rated in terms of
High voltage transmission lines are transposed because then
The power factor of an open ended cable can be improved by
The maximum short circuit current occurs in case of
A fault occurring at the terminal of an unloaded synchronous generator operating at its rated voltage has resulted in the following values of currents and voltages
Iao = j2.37Pu Ia1 = j3.05 Pu Ia2 = j0.68 Pu
In an overcurrent protection the retting of the earth fault relay is
Time response of an indicating instrument is decided by which of the following systems ?
A 50 mA basic d'Arsonval movement with an internal resistance of 500W is to be used as a voltmeter. The value of the multiplier resistance required to measure a full scale voltage range of 0-5 volts is
In measuring resistance by voltmeter ammeter method, the voltmeter can be connected either across supply or across the resistance. If the resistance is low, the voltmeter should be connected
A Wheatstone bridge has got three resistances taken in clockwise direction as 120W, 150W & 150W. The value of fourth resistance for null balance would be
Inductance is measured by which one of the following ?
A Maxwell inductance capacitance bridge is used for the measurement of inductance by making comparison with a standard capacitance value. Voltmeter is used to measure voltage, while an ammeter is used to measure current.
Electronic voltmeters which use rectifiers employ negative feedback. This is done
Guard circuits are used in insulation resistance measurements to
Which of the following instrument does not use the effect of current for measurement purposes?
One wattmeter method is used to measure power in three circuits when
In two wattmeter method, if power factor is 0.5, then one of the wattmeters will read
Which is the integrating instrument ?
The ratio error of a current transformer is due to
An electrodynamic wattmeter is not considered suitable for low power factor circuits due to
A Q-meter works on the principle of
Which instrument has the same calibration for ac & dc values ?
Which voltmeter has least power consumption?
A ballastic galvanometer is used for the measurement of
The bridge used for the precise measurement of inductance over a wide range is
When a transistor is connected in common emitter mode it will have
A bridge used to measure the inductance haring large time constant is
Hay’s Bridge is suited for the measurement of Inductance of a coil with a large time constant.
The concentration of minority carries in an extrinsic semiconductor under equilibrium is
In a p-n junction diode under reverse bias, the magnitude of electric field is maximum at
As compared to an LED, an LCD has the distinct advantage of
CE configuration is the most preferred transistor configuration when used as a switch because it
In a NPN transistor, when emitter junction is forward biased and collector junction is reverse biased, the transistor will operate in
In normally biased NPN transistor the main current crossing the collector junction is
Which junction transistor is preferred for high input and low output impedance ?