BASIC ELECTRONICS — EE

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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


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