In a transformer
One 20 V, 100 W bulb is connected in series with the primary of a 200 V, 10 kVA transformer. If its secondary is open circuited, then the bulb will have
A metal resistor has resistance of 10W at OºC and 11 ohms at 160ºC, the temperature coefficient is
A 100 W, 200 V filament lamp has operating temperature of 2000ºC. The filament material has resistance temperature coefficient of 0.005 at OºC per ºC. The current taken by the lamp at the instant of switching with 200 V supply with filament temperature of 20ºC will be
Which one of the following has the least value of form factor?
In square wave, the rms value and average value are same (whatever peak magnitude presents in that square wave). So, the form factor is equal to one. But, in other kind of waveforms (for example, sine, triangle, rectangle, etc), the average value is less than the rms value. So, the value of form factor is greater than one. Hence, as compared to other waveforms, square wave has least value of form factor.
Power factor of the magnetising component of a transformer is
When a 100 mA alternating current with a frequency of 1 kHz flows in the primary of two coupled coils, the secondary voltage is 1V. The mutual inductance between the coils is
A coil with 1000 turns carrying a current of 8A produces a flux of 6×10–6 Wb. The inductance of the coil would be
A shunt generator produces 450A at 230 V. The resistance of shunt field and armature are 50W and 0.025W respectively. The armature voltage drop will be
A 4-pole dynamo with wave wound armature has 51 slots containing 20 conductors. The voltage induced is 357 V and the speed is 8500 rpm. The flux per pole will be
Series reactors are installed at strategic locations of power system to
The inductance is introduced in the cables in the form of
Load saturation characteristics of a dc generator gives relation between
Equalizer rings are required in lap winding dc machine
According to the fuse law, the current carrying capacity varies as
In electrodynamometer, ammeter, the deflection of the pointer is proportional to
In which of the following transformers, is the secondary winding always kept closed ?
Which of the following transducer requires a high input impedance preamplifier for proper measurements ?
The shape of the curve between the flux density and ampere turns/m is correctly represented by which of the following figures ?
Which loss in a dc generator significantly varies with the load current ?
The ratio of starting torque to fully load torque is least in case of
Correct Answer :- a
Explanation : From torque current characteristic, we get that torque at no load or starting torque is equal to zero. As load increases, speed decreases and armature current increases so as torque also increases linearly, if effect of armature reaction is neglected.
A rheostat differs from potentiometer in the respect that
The equivalent resistance at the points X1 and X2 in the circuit shown below
With the sole purpose of an alternating current is to produce heat, the selection of conductor is based on
In case of delta connected circuit, when one resistor is open, power will be
Correct Answer :- c
Explanation : Power consumed in case of balanced delta connection P = Vph2/Req. Req = 2R/3.
So, P = 3Vph2/2R.
If one resistor is removed from a 3 - phase delta connected circuit, then the circuit will be converted into single phase circuit having two resistors in series.
P’ = Vph2/Req. Req = 2R.
So, P’ = Vph2/2R.
P’ = P/3
Permitivity is expressed in terms of
The transition region in an open circuited p-n junction contains
In an unbiased p-n junction, zero current implies that
A null type of instruments as compared to a deflection type instrument has
Accelerated again is done on coils for standard resistors in order to
DC motor with self loading properties is
Regenerative braking on shunt motors is used when
Which of the following methods is most effective in finding out the no load losses in a large dc shunt motor ?
Which domestic utility item has highest power rating ?
Which equipment provides fluctuating loads ?
In case of medium sized induction motor the power factor will be maximum at
Efficiency is secondary consideration in case of
In a transmission line following are the distributed constants
In case the characteristic impedance of the line is equal to the load impedance
Which type of insulators are used on 132KV transmission lines ?
Under no load conditions, the current in a transmission line is due to
A bus bar is rated by
The function of breather in a transformer is
Which loss in a transformer varies significantly with load ?
Voltage remaining constant, if the frequency is increased then
A parallel plate capacitor is filled with two dielectrics of E1 and E2 lengthwise equally. The
capacitance of the combination is
The supply voltage |V| in the diagram below is
If the secondary of a 1:10 step up transformer is connected to the primary of a 1:5 step up transformer, the total transformation ratio will be
Which of the following transformers is smallest ?
When transistors are used in digital circuits they usually operate in the
Three different Q points are shown on a dc load line. The upper Q point represents the
Junction field effect transistor (JFET) contain how many diodes ?
The ratio of available power from the dc component of a full-wave rectified sinusoid to the available power of the rectified sinusoid is
If the resistance in a series RC circuit is increased, the magnitude of the phase
Two transformer of ratings 600 kVA and 350 kVA are connected in parallel to share a load of 800 kVA. The reactance of the transformers, referred to the secondary sideare 0.0198W and 0.0304W respectively (resistance negligible). The load shared by the two transformers will be, respectively
A separately exited dc motor has an armature resistance of 0.5W. It runs off a 250V dcsupply drawing an armature current of 20A at 1500 rpm. The torque developed for an armature current of 10A, for the same fieldcurrent, will be
A generating station has a maximum demand of 50 MW, a load factor of 60%, a plant capacity factor of 45% and if the plant while running as per schedule, were fully loaded, running energy produced will be
A distribution transformer usually is a
Which of the following distribution system is the simplest and have lowest installation cost
A random noise generator produces a signal
A zener diode voltage regulator has load requirement of 12V and 2 Amp. The zener diode's minimum current requirement is 0-2A. The minimum voltage at input is 24V. What isthe maximum efficiency of circuit ?
With the positive probe on an NPN base, an ohmmeter reading between the other transistor terminal should be
The principle of operation of an LVDT is based on variation of
Rectifier moving coil instruments respond to
To the y-input of a CRO a signal defined by 10 sin 100t is applied. To the x-input, the signal 10 cos 100t is fed. The gain for both x-channel and y-channel is same. The screen shows
A short circuit test on a transformer gives
Which of the following connection of transformer will give the highest secondary voltage ?
For an alternator when the power factor of the load is unity
The advantage of salient poles in an alternator is
In a 440V system, in order to obtain the minimum cost and maximum benefits, the capacitor should be installed
Which of the following relations between apparent power (kVA), true power (kW) and reactive power kVAR is true ?
Power distribution by cable is generally adopted for line length
Supplier's fuse, which is provided in domestic wiring system is
A supply voltage of 230V, 50 Hz is fed to a residential welding. Write down its equation for instantaneous value
A transistor has a Bdc of 250 and a base current, IB of 20 mA. The collector current IC, equals
A collector current is the current, directly passing in the transistor through a collector.
The formula to determine the collector current is -
beta = Ic/Ib
Where Ic = 20 mA,
Therefore Ib -
Ic = Beta × Ib
Ic = 250 × 20/1000000
Ic = 5000/1000000
Ic = 5
Answer: The collector current is 5mA
In a CE configuration, an emitter resistor is used for
A diode can be used as a frequency multiplier because of its
Which of the following is not characteristics of an oscillator ?
You can find the zener diode in
A series resonant circuit has an inductive reactance of 1000W, a capacitive reactance of 1000W and a resistance of 0.1W. If the resonant frequency is 10 MHz, then the bandwidth of the circuit will be
The circuit shown in figure-I is replaced by that in figure-II. If current 'I' remains the same than Ro will be
When the resistor voltage in a series RL circuit becomes less than the inductor voltage, the phase angle :
As the inductor voltage decreases, the voltage across the resistor increases and therefore the current also increases. Ultimately, the inductor voltage is zero, all of the voltage source output is across the resistor, and the current is at its maximum value.When the resistor voltage in a series RL circuit becomes less than the inductor voltage, the phase angle increases.
Diversity factor is equal to
The starting capacitor of a single phase motor is
The short coming of repulsion motor is
A belt-driven cumulatively-compounded dc generator is delivering power to the dc mains. If the belt snaps then the machine will run as a
In a loaded dc generator, if the brushes are given a shift from the interpolar axis in the direction of rotation, then the commutation will
i1 in the circuit is
In a single phase power factor meter, the controlling torque is
In calibration of a dynamometer wattmeter by potentiometer, phantom loading arrangement is used because
The illumination level in houses is in the range
One lumen per square metre is the same as
For the power factor correction of welding transformer, a capacitor is usually connected on
The arc has
The efficiency of a welding motor generator is usually in the range of
Skewing of rotor slots helps in
In a constant power type load
If a cable is to be designed for use on 1000 kV which insulation would you prefer ?
In a CRO, the focusing anode is located
The mutual inductance between two coils having self inductances 3 henry and 12 henry and coupling coefficient 0.85 is