BASIC ELECTRONICS — EE
The power taken by a 3-phase load is given by the expression
(3)^1/2 VL*ILcosφ
The magnitude of variation in the output voltage for a 10 V regulated dc power supply of 0.002% regulation will be
0.2mV
Resistance of a wire is r ohms. The wire is stretched to double its length, then its resistance in ohms is
4r
Ripple factor of a full-wave rectifier without filter will be
0.48
If the reading of the two wattmeters in the 2-wattmeter method of power measurement are 4.5 kW and 3.5 kW respectively and the latter reading has been obtained after reversing the current coil of the wattmeter. What will be the total power in kW?
1 kW
A voltage source having an open-circuit voltage of 100 V and internal resistance of 50Ω is equivalent to a current source
2A in parallel with 50Ω
Q factor of an inductive coil is given by
2πr/R
Three capacitors of value 8uF, 16uF and 32uF are connected in series, the total capacitance will be
32/7 uF
The theoretical maximum efficiency of a Bridge rectifier circuit is
81.2%
The color band sequence of a resistor is grey, blue, gold, and gold. The range in which its value must lie so as to satisfy the tolerance specified is between
8.17 Ω and 9.03 Ω
Load factor is defined as the ratio of
Average Demand / Max. Demand
The crawling in an induction motor is caused by
Harmonics developed in the motor
JFET has main drawback of
Having small gain-bandwidth product
The unit of inductance is
Henry
Which single phase motor would you select for a tape recorder?
Hysteresis motor
The efficiency of a transformer is maximum when
Its Cu loss equals iron loss
Superposition theorem can be applicable only to circuits having _____ elements.
Linear bilateral
The demand factor for the electrical system is the ratio of
Maximum demand to connected load
The relation between frequency, speed and number of poles is given by
Ns=120*f/p
Which of the following power plant has the maximum efficiency?
Nuclear
The combined resistance of two equal resistors connected in parallel is to
One half the resistance of one resistor
Under the condition of resonance, RLC series circuit behaves as a
Purely resistive circuit
The Q-factor of a coil is given by
Reciprocal of its power factor
The colour code of a resistor nominal value 2 KΩ ± 10% is
Red, violet, red and silver
Transformer core is laminated to
Reduce the eddy current losses
Reduction in the capacitance of a capacitor-start motor results in reduced
Starting torque
The starting winding of a single-phase motor is placed in
Stator
An electric motor in which rotor and stator fields rotate simultaneously is called a
Synchronous
In forward mode NPN BJT, if we increase the voltage Vcc, the collector current increases
due to both the reasons (B) and (C) (B) due to base width decrease less carrier recombine in the base region. (C) as the gradient of the minority carriers in the base region becomes steeper.
The relationship between the frequency of ac wave and the time period is given by
f=1/T
An intrinsic semiconductor at absolute zero temperature
has a large number of holes
The emission of electrons in a vacuum diode iis acchieved by
heating
FET is advantageous in comparison with BJT because of
high input impedance
Which of the following generating stations has the minimum running cost?
hydro-electric station
Cells are connected in parallel in order to
increase the current available
Ideal operational amplifier has input impedance of
infinity
In a differential amplifier an ideal CMRR is
infinity
The "Superposition Theorem" is essentially based on the concept of
linearity
An electric machine will have high efficiency when
losses are low
In a Zener diode large reverse current is due to
lower resistance in reverse biased region
The effect of increasing the length of the air gap in an induction motor will be to increase
magnetising current
A UJT contains
one pn junction
The difference between synchronous speed and the actual speed of an induction motor is known as
slip
A switching voltage regulator can be of the following type:
step-down
In an N-type semiconductor, the concentration of minority carriers mainly depends upon
the number of donor atoms
The barrier voltage (Vr or Vo) in a junction diode is the effect oof
the recombination of charge carrier across the junction leaving behind the opposite charged ions.
An emitter follower has high input impedance because
there is negative feedback in the base emitter circuit
The power factor of a purely resistive circuit is
unity
A step-up transformer increases
voltage
For the operation of a depletion-type N-MOSFET, the gate voltage has to be
zero
For the circuit shown in Fig.1, the output voltage is given by
Vo=Rf/R1 (V2-V1)+V2
Which of the following bulbs will have the least resistance?
115V,100W
The typical operating voltage for LEDs ranges from
1.5V to 2.5V
The input of an ac circuit having p.f of 0.8 lagging is 20kVA. The power drawn by the circuit is _____ kW.
16
In an 8-ole wave connected motor armature, the number of parallel paths are
2
In India, electrical power is transmitted by
3-phase 3-wire a.c. system
The input resistance of a common-collector configuration will be of the order of
300KΩ and above
The current flow through a Ge PN junction diode with a forward bias of 0.22 Volt and a reverse saturation current of 1mA at 25C is around
5.22 A
The rms value of a sinusoidal 100V peak to peak is _____ volt.
50/(2)^1/2
Which of the following statements is not true?
A capacitor offers high impedance to ac but very low impedance to dc.
When a low resistance is connected in parallel with a high resistance, the combined resistance is
Always less than the low resistance
Star-delta starter of an induction motor
Applies reduced voltage to stator
In ac circuit the product of voltage and current is known as
Apparent power
Centrifugal switch is provided for disconnecting the auxiliary winding in a
Capacitor-start motor
A DC series motor is best suited for driving
Cranes and hoists
Which of the following will remain the same in all parts of a series circuit?
Current
A battery is a source of
DC voltage
In a DC series motor increase in load currents results in
Decrease in speed
The speed of an induction motor
Decreases slightly wit the increase of load
In an R-L-C circuit, the phase of the current with respect to the circuit voltage will be
Depends upon the value of L and C
During charging, the electrolyte of a lead acid cell becomes
Diluted
Transformer cores are built up from lamination rather than from solid metal so that
Eddy current loss is reduced
Watt hour is the unit of
Electric energy
Capacitor that can have the highest capacitance value is
Electrolytic
The frequency of the secondary voltage of a transformer will be
Equal to the primary voltage
The voltage ratio of the transformer is given as
Es/Ep
The CE configuration amplifier circuits are preferred over CB configuration amplifier circuits because they have
Larger amplification factor
As compared to shunt and compound motors, series motor have the highest torque because of its comaparatively _____ at the start.
Larger armature current
A network that does not have either voltage or current sources is called
Passive network
The most commonly used type of electron emission in electron tubes is
Photo-electron emission
In an ac circuit, the ratio of kW/kVA represents
Power factor
Static Capacitors are used for
Power factor improvement
In two wattmeter method of power measurement, if one of the wattmeter shows zero reading, then it can be concluded that
Power factor is 0.5 lagging
Thevenin's equivalent circuit consists of
Series combnation of Rth, Eth
Which DC motors has approximately constant speed?
Shunt motor
Stator core of an induction motor is made of
Silicon steel stampings
Rotating magnetic field is produced in a
Three-phase induction motor
The power-factor at resonance in R-L-C circuit is
Unity
Voltage equation of a dc motor is
V=Eb+IaRa
Which type of loss in not common to transformers and rotating machines?
Windage loss
The frequency of DC supply is
Zero
The starting torque of a 1-phase induction motor is
Zero
A device whose characteristics are very close to that of an ideal current source is
a BJT in CB mode
The equivalent current-source representation for a voltage-source with open circuit voltage 12 V and internal resistance 3 ohms is
a current-source of strength 4A in shunt with resistance of 3 ohms.
The following components are all active components
a diode, a BJT, and a FET
For thermionic emission
a material with low work function is preferable.
A UJT has
all of these characteristics (A) stable negative resistance characteristics. (B) low firing current. (C) use as a waveform generator.
Capacitors for integrated circuits
can be made using silicon dioxide as the dielectric
Which of the following motors has a high starting torque?
dc series motor
When forward bias is applied to a junction diode,it
decreases potential barrier
