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The output voltage of a battery drops from 100 V with zero load current to 80 V when load current is 2 A. The internal resistance of the battery is
Let the internal resistance of the battery is r.
When load current is zero, output voltage = 100 V
Battery voltage = 100 V
When load current is 2 A, the output voltage is 80 V
⇒ 100 – 2r = 80
⇒ r = 10 Ω
The voltage transformation ratio of a transformer is equal to the ration of:
In transformers, voltage transformation ratio is the ratio of secondary induced emf to primary induced emf.
Assertion (A): When a series RLC circuit is in resonance, the current flowing in the circuit is maximum.
Reason (R): The inductive reactance and the capacitive reactance are equal in magnitude at resonance.
We know that, in a series RLC circuit impedance is given by
Current flowing in the circuit is given by I = V/Z
Where, Z is impedance
R is resistance
XL is inductive reactance
XC is capacitive reactance
At resonance condition, the inductive resistance is equal to capacitive reactance.
At this condition, Z = R which is minimum value of impedance
At minimum impedance, the current flowing in the circuit is maximum
Hence both A and R are true, and R is the correct explanation of A.
Given unit A/m defines which terms of magnetic circuit.
Which instrument is the cheapest disregarding the accuracy.
As torque/weight ratio is more in PMMC instruments, the accuracy is very high in these instruments. PMMC instruments are used in rectifier type instruments, hence these are also equally accurate.
Moving iron instruments has the least accuracy among all the given instruments.
The order of accuracy in descending order
PMMC > Electrodynamometer > Moving Iron
The tips of the electrodes, for the spot welding are made of:
Spot welding means the joining of two metal sheets and fusing them together between electrode tips at suitably spaced intervals by means of heavy electric current passed through the electrodes.
The electrodes are made up of copper or copper alloy and are water cooled.
The welding current varies widely depending upon the thickness and composition of plates. It varies from 1000 to 10000 A, and voltage between the electrodes is usually less than 2 V.
For measurement of radio frequency A.C. signal ________ type meter is used.
Thermal instruments are used for the measurement of radio frequency AC signals. They are very useful when used as transfer instruments to calibrate dc instruments by potentiometer and standard cell. These instruments are suitable for both AC and DC.
Which of the following is the information retrieval service?
The synchronous motor is:
The synchronous motor is a constant speed motor and it always runs as at synchronous speed.
Due to the magnetic locking between stator and rotor poles synchronous motor is not self-starting and there is no starting device to accelerate the rotor to near synchronous speed.
It can be made self-starting by providing damper windings on rotor poles or by using pony motors.
Superposition theorem is used to obtain current in or voltage across any conductor of the:
Superposition theorem is valid for only linear bilateral networks. We can apply superposition theorem for both DC and AC circuits.
Hence it is used to obtain current in or voltage across any conductor of the linear network.
A CRO cannot be used for direct measurement of CRO
We can directly measure voltage, current and frequency by using CRO. We cannot directly measure power by using CRO.
Where will the deleted files be stored?
In computing, the Trash (also known as the Recycle Bin in Windows) is the temporary storage for files that have been deleted in a file manager by the user, but not yet permanently erased from the file system.
Typically, a recycle bin is presented as a special file directory to the user, allowing the user to browse deleted files, undelete those that were deleted by mistake, or delete them permanently (either one by one, or by the "Empty Trash" function).
The adverse effect(s) of acid rain is(are)
When the quantity of acids in the raining water is more than the average, then such rain is called 'Acid rain'.
We are aware that normally rainwater has a pH of 5.6. When the pH of the rainwater drops below 5.6, it is called acid rain.
Acid rain refers to the ways in which acid from the atmosphere is deposited on the earth’s surface. Oxides of nitrogen and sulphur which are acidic in nature can be blown by wind along with solid particles in the atmosphere and finally settle down either on the ground as dry deposition or in water, fog and snow as wet deposition.
Acid rain is a byproduct of a variety of human activities that emit the oxides of sulphur and nitrogen in the atmosphere. As mentioned earlier, burning of fossil fuels (which contain sulphur and nitrogenous matter) such as coal and oil in power stations and furnaces or petrol and diesel in motor engines produce sulphur dioxide and nitrogen oxides.
SO2 and NO2 after oxidation and reaction with water are major contributors to acid rain because polluted air usually contains particulate matter that catalyses the oxidation.
2SO2 (g) + O2 (g) + 2H2O (l) → 2H2SO4 (aq)
4NO2 (g) + O2 (g)+ 2H2O (l) → 4HNO3 (aq)
The bad effects of acid rain
Which of the following motor does not use a centrifugal switch?
To make the single phase induction motor self-starting, it is temporarily converted into two-phase motor during starting. For this purpose, the stator of a single phase motor is provided with extra winding known as starting winding in addition to the main winding. This is invariably done with a capacitor in series with the second winding.
Shaded pole motor is used to drive the devices which require low starting torque. It doesn’t have any centrifugal switch.
Which type of lamp holder from the following is fitted directly on the wooden board?
Batten Holder: This type of lamp holder is fitted directly on the wooden board, which itself is fixed on the wall. The lamp is then supported in the batten holder.
Pendant Holder: When the bulb is to be suspended from the ceiling rose, this type of holder has to be used for holding the lamp.
Angle Holder: Angle holders are used when the light of the lamp is needed at a certain angle. These are directly fixed to the walls.
Bracket Holders: These are used where direct light is needed in the room. These are also used on table lamps. Brackets used with such type of holders are made of brass material.
WaterTight Bracket Holder: These are provided with tubular glasses with watertight covers. These are mainly used for street lighting. They are also used for supporting bulbs outside the house premises.
Main purpose of using oil in oil circuit breaker is to:
In the oil circuit breaker, oil is used as a dielectric or insulating medium for arc extinction. In oil circuit breaker the contacts of the breaker are made to separate within an insulating oil.
Advantages of oil as an arc quenching:
To determine the polarity of the voltage drop across a resistor, it is necessary to know.
To determine the polarity of the voltage drop across the resistor, it is necessary to know the direction of the current through the resistor.
The terminal entering the current gives a positive sign of voltage drop.
The internal resistance of an ideal voltage source and an ideal current source respectively are (in ohms)
Ideal voltage source: An ideal voltage source have zero internal resistance.
Practical voltage source: A practical voltage source consists of an ideal voltage source (VS) in series with internal resistance (RS) as follows.
An ideal voltage source and a practical voltage source can be represented as shown in the figure.
Ideal current source: An ideal voltage source has infinite resistance. Infinite resistance is equivalent to zero conductance. So, an ideal current source has zero conductance.
Practical current source: A practical current source is equivalent to an ideal current source in parallel with high resistance or low conductance.
Ideal and practical current sources are represented as shown in the below figure.
Regarding HRC fuses which of the following statement is not correct?
In HRC (High Rupturing Capacity) fuse, the fuse wire or element can carry short circuit heavy current for a known time period. During this time if the fault gets removed, then it does not blow off. Otherwise, it blows off or melts.
What is the typical value of VBE set in PNP Ge transistor?
Light can travel in vacuum but not sound, because ________.
Reluctance of magnetic path is:
Reluctance opposes the passage of magnetic flux lines. Reluctance is analogous to resistance.
We can define the reluctance as,
We know that,
Where H is field strength
N is the number of turns in a coil
l is mean length of flux in a magnetic circuit
I is current through the coil
The flux in a magnetic circuit is given by
Now, we can define reluctance as
Strait of Malacca separates which two land masses?
If the load current and flux of a DC motor are held constant, and voltage applied across its armature is increased by 10%, its speed will
We know that, in a dc motor
As voltage applied across its armature is increased by 10%, back emf also gets increased by 10%.
As flux is constant and speed is directly proportional to back emf, speed also gets increased by 10%.
Mutual inductance between two magnetically coupled coils depends on
The mutual inductance between two magnetically coupled coils is given by
Where μr is relative permeability of the core
N is the number of the turns of the coil
A is cross-sectional area of their common core
Hence, the mutual inductance depends on all the above factors.
The following figure represents:
The frame of an induction motor is made of:
In an induction motor, stator or the stationary part consists of three-phase winding held in place of slots of a laminated steel core. This steel core is enclosed and supported by closed grained cast iron or a steel frame.
Who has assumed the charge as Vice Chief of the Naval Staff on 30 Jan 2019?
A hacker contacts your phone or E-mails and attempts to acquire your password is called
A Threat is any circumstance or event with the potential to cause harm to the system or activity in the form of destruction, disclosure, and modification of data, or denial of service. A threat is a potential for harm.
Some of the common terms associated with threats and their description are as follows:
Spoofing: A spoofing attack is when a malicious party impersonates another device or user on a network in order to launch attacks against network hosts, steal data, spread malware, or bypass access controls. There are several different types of spoofing attacks that malicious parties can use to accomplish this. They are IP Address Spoofing Attacks, ARP (Address Resolution Protocol) Spoofing Attacks, DNS Server Spoofing Attacks, etc.
A software bug is an error, flaw, failure or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways.
What is the approximate value of average resistance of a human body?
Under dry conditions, the resistance offered by the human body may be as high as one megaohm. Wet or broken skin may drop the body's resistance to 1000 ohms. Adding that, high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 ohms.
Which element is most electronegative among Arsenic, Nitrogen and Phosphorus?
The force experienced by a current carrying conductor lying parallel to a magnetic field is ________
The force experienced by a current carrying conductor lying in a magnetic field is with an angle θ is
F = Bil sinθ
As the conductor is lying parallel to a magnetic field, θ = 0°
Hence the force = zero
An inductor at t = 0+ with zero initial conditions acts as
An inductor at t = 0+ acts as an open circuit and at steady state acts as short circuit
A capacitor at t = 0+ acts as short circuit and at steady state acts as an open circuit
Which one is an input device of the computer?
Components of Computer
Input devices are used to enter data or instructions into a computer.
Output unit receives the information from the processing unit and provides the result in a human-readable form.
Storage devices are the computer hardware used to remember/store data.
Select the incorrect statement.
A single-phase induction motor
1. requires only 1 winding
2. can rotate in one direction only
3. is not self-starting
When single phase AC supply is given to stator winding, it produces alternating flux i.e. which alternates along one space axis only.
It is not synchronously revolving (or rotating) flux, thus it cannot produce any rotation. Hence single phase induction motor is not self-starting.
To overcome this problem and to make the motor self-starting, it is temporarily converted into two-phase motor during starting. For this purpose, the stator of a single phase motor is provided with extra winding known as starting winding in addition to the main winding. These two winding are placed across the single phase supply. It can rotate in both the directions.
The most common and best bridge method for precise measurement of inductance over a wide range is
Maxwell’s inductance capacitance bridge is used for the measurement of an inductance of medium Q coils.
Hay’s bridge is used to measure for the measurement of an inductance of high Q coils.
Anderson Bridge is the most common and best bridge method for precise measurement of inductance over a wide range.
Wein Bridge is used to measure the frequency.
Three resistances of 1 ohm, 2 ohms and 3 ohms are connected in delta. These resistances are to replace by star connection as shown in the figure below, maintaining the same terminal conditions. The value of the highest resistance in the star will be
To convert delta to star,
A coil having 90 turns is connected to a 120 V, 60 Hz source. If the effective value of the magnetizing current is 4 A, then calculate the value of inductance of the coil.
Given that, emf (E) = 120 V
Magnetizing current (I) = 4 A
Frequency (f) = 60 Hz
Reactance = 120/4 = 30 Ω
We know that, XL = 2πfL
The average of all the instantaneous values of a sinusoidal quantity over a cycle is:
The average value of a sinusoidal wave is zero
The rms value of a sinusoidal wave is
Which of the following alloy is used for making clocks and scientific instruments?
Invar is an alloy composed of Iron, nickel, and Carbon where Iron is a major component with 63%, nickel with 36% and Carbon with 1%. Invar is an alloy used for making clocks and scientific instruments because of its property of negligible coefficient of expansion.
The active power in a delta connected system of 440V with a balanced load of inductive reactance of 3Ω & resistance of 4Ω per phase is
Given that, line voltage (VL) = 440 V
Resistance (R) = 4 Ω
Inductive reactance (XL) = 3 Ω
In delta connection, phase voltage = line voltage
Phase voltage (Vph) = 440 V
Active power P = 3VphIphcosϕ
⇒ P = 3 × 440 × 88 × 0.8 = 92.928kW
Which among the following glasses can cut off the UV rays?
At power frequencies, skin and proximity effects are ________ frequency
Skin Effect: The tendency of alternating current to concentrate near the surface of the conductor is known as skin effect. The skin effect depends on the following factors.
b) Diameter of the conductor
c) Shape of the conductor
The skin effect increases with the increase of cross section, permeability and supply frequency. It reduces with the increase in resistivity of the conductor material.
Proximity Effect: The alternating flux in a conductor is caused by the current of the other nearby conductor. This flux produces a circulating current or eddy current in the conductor which results in an apparent increase in the resistance of the wire. Thus, more power losses in the windings. This phenomenon is called the proximity effect.
Both skin effect and proximity effect are negligible at small frequencies.
Electroplating is done for:
Electroplating is defined as the deposition of a metal over any metallic or non-metallic surfaces. Electroplating is usually employed
1. To protect the metals from corrosion by atmospheric air, moisture and CO2
2. To give the reflecting properties to reflectors
3. To replace worn out metals
4. To give a shiny appearance to articles
Where was the Vaikom Satyagraha (1924-25) started?
Vaikom Satyagraha was a Satyagraha in Travancore, Kerala against untouchability in Hindu society.
Hence, 1 is the correct answer.
Which city is called as the Pittsburgh of India?
The schedule speed of a given train when running on a given service (with a given distance between stations) is affected by:
Schedule Speed: The ratio of the distance covered between two stops to the total time of the run including the time for the stop is known as schedule speed. It is denoted with Vs
Where Ts is the scheduled time in hours
Factors affecting the schedule speed of a train are:
A transistor has the following currents:
IB = 25 mA
IC = 4.975 A
Then IE is equal to
We know that
IE = IB + IC
IE = Emitter current
IB = Base current
IC = Collector current
IE = IB + IC = 0.025+4.975=5A
The following statements associated with Buchholz relays is not true:
If the plates of a capacitor are brought closer to each other, what will be the effect on capacitance?
Which of the following transformer will be largest in size:
For a fixed kVA rating, more the designed frequency of transformer then lesser will be cross sectional area of the core. Hence lesser will be the size and weight of transformer.
All the transformers given in the options have same kVA rating. Hence the transformer with lowest designed frequency has largest size.
The coefficient of the adhesion improves due to the presence of:
The coefficient of adhesion (μ): It is defined as the ratio of the tractive effort (Ft) to propel the wheel of a locomotive to its adhesive weight (W).
The coefficient of the adhesion improves due to the presence of:
The coefficient of the adhesion reduces due to the presence of:
The load factor for domestic loads may be taken
Damping torque is essential to
The deflecting torque is used for deflection, the controlling torque acts opposite to the deflecting torque. So before coming to rest the pointer always oscillates due to inertia, so to bring the pointer rest within a short time by reducing oscillations, we use damping torque without effecting controlling torque (or) inertia.
The following mechanism can be used for producing damping torque.
1. Air friction damping
2. Fluid friction damping
3. Eddy current damping
Swamp resistance and condenser are used
Swamping resistor and condenser are used to reduce the frequency error in MI instruments.
In moving iron instruments, the change in frequency causes an error due to the change in magnitude of eddy currents set up in the metal portion of the instruments.
The reactance of the operating coil changes by the change in frequency.
At high frequencies, the meter will give a reading lower than the actual value and at low frequencies, meter give a reading higher than the actual.
This type of error can be eliminated only if the impedance of the coil is independent of the frequency. This is achieved by having a capacitance in shunt with the swamping resistance of the coil as shown in the figure.
In the above figure, C is condenser and r is swamping resistance, whereas L and R represent the reactance and resistance of operating coil in moving iron instrument.
During the operation of a connecting a busbar in parallel with an incoming alternator the:
During the operation of a connecting a busbar in parallel with an incoming alternator, the following condition should be satisfied:
When excitation of the synchronous motor is increased up to normal excitation from under excitation, the armature current
By observing V curves,
When excitation of the synchronous motor is increased up to normal excitation from under excitation, armature current decreases
When excitation of the synchronous motor is increased to overexcitation from normal excitation, armature current increases
If two or more components are connected in _________, they have the same potential difference (voltage) across their ends.
If two or more components are connected in parallel, they have the same potential difference across their ends but the current flowing through them will be different.
If two or more components are connected in series, the current flowing through them will be different, but they have different voltage drops across them.
A current source i(t) = 1.25 cos (5t – 15°), a driving load = 12∠53°Ω. What is the value of the complex power delivered by the source to the load?
Given that, i(t) = 1.25cos(5t − 15∘)
z = 12∠53∘Ω
Complex power delivered by the source to the load is
Which of the following fuels causes minimum environmental pollution?
Hydrogen fuel is a zero-emission fuel when burned with oxygen (if one considers water not as an emission) or used in a contained cell (allowing to react galvanically) also capable of 'reversing' the reaction if needed.
Number of immobile contacts in double oil circuit breaker is:
An electrical circuit breaker is a switching device which can be operated automatically or manually for protecting and controlling an electrical power system.
The oil used in the oil circuit breaker will absorb arc energy while decomposing.
In double break bulk oil circuit breaker, there are two fixed contact and are bridged by one moving contact. The moving contact is fitted with a driving mechanism of the oil circuit breaker by means of an insulated rod.
Which of these poets were awarded 'Saraswati Samman 2017' on 22 January 2019?
In any bilateral network, if a source of e.m.f. E in any branch produces a current I in any other branch, then same e.m.f. acting in the second branch would produce the same current I in the first branch. This statement is associated with
Reciprocity theorem states that in any branch of a network, the current (I) due to a single source of voltage (V) elsewhere in the network is equal to the current through the branch in which the source was originally placed when the source is placed in the branch in which the current (I) was originally obtained.
It is applicable for only single source networks.
In the circuit (a), the value Ia is obtained for a voltage source V. According to reciprocity theorem, this current is equivalent to Ib in circuit B.
In a resistance furnace, the atmosphere is:
Resistance furnace is an electric furnace in which heat is generated by conductors that offer resistance to the passage of a current through them. Resistance furnaces are widely used in heat treatment, for heating prior to pressure shaping, and to dry or melt materials.
Resistance furnaces are readily mechanized and automated, thus alleviating the work of personnel and facilitating the inclusion of such furnaces in automatic transfer lines. In addition, they are compact. Such furnaces provide a secure environment for various processes.
A resistance furnace may be well sealed, in which case the heating is carried out in a vacuum, or it may contain either a gaseous medium that prevents oxidation or a special atmosphere for chemical case hardening. The special atmosphere in these type of furnaces is oxidizing.
A magnetizing force of 800 AT/m will produce a flux density of ______ in air.
Given that, Magnetic force (H) = 800 AT/m
As it is air, μr = 1
We know that,
In dynamometer wattmeter the compensation coil
In dynamometer wattmeter, the pressure coil is designed for having a low value of resistance so that the high value of current passes through it. This current produces the deflecting torque on the moving coil.
In a low power circuit, the value of the current is high, and that of the power is low. This high-value current causes the error in the wattmeter reading. To reduce this error, the compensation coil is used in the circuit.
Compensating coil has an equal number of turns of the current coil and is connected in series with a voltage coil or pressure coil. It carries current equal to the sum of two currents i.e. load current plus pressure coil current. The pressure coil is placed such that the field produced by the compensating coil is opposed by the field produced by pressure coil as shown in the above circuit diagram.
What will be the total current flowing in the circuit by applying 60 V at the terminals A and B?
The equivalent resistance of the circuit is,
R = 60 Ω
Current (I) = 60/60 = 1 A
The ‘cogging’ of an induction motor can be avoided by:
Sometimes induction motor refuses to start at all. Sometimes it happens because of the low supply voltage. But the main reason for starting problem in the motor is because of cogging in which the slots of the stator get locked up with the rotor slots.
As we know that there is a series of slots in the stator and rotor of the induction motor. When the slots of the rotor are equal in number with slots in the stator, they align themselves in such way that both face to each other and at this stage the reluctance of the magnetic path is minimum and motor refuse to start. This characteristic of the induction motor is called cogging.
Apart from this, there is one more reason for cogging. If the harmonic frequencies coincide with the slot frequency due to the harmonics present in the supply voltage then it causes torque modulation. As a result of it, cogging occurs. This characteristic is also known as magnetic teeth locking of the induction motor.
This problem can be easily solved by adopting several measures. These solutions are as follows:
1. The number of slots in the rotor should not be equal to the number of slots in the stator.
2. Skewing of the rotor slots, that means the stack of the rotor is arranged in such a way that it angled with the axis of the rotation.
The e.m.f induced is 2 V when current is changing at the rate of 0.5 A/s. The self-inductance of the coil is:
Given that, emf (E) = 2 V
Rate of change of current = 0.5 A/s
We know that, induced emf
⇒ 2 = L(0.5) ⇒ L = 4H
For DC motor magnets, _______ is preferred:
Applications of different magnetic materials:
In the following figure, the equivalent resistance at terminals A and B will be
In the given circuit, 50 Ω, 75 Ω and 50 Ω resistors are connected in parallel.
The equivalent resistance of this parallel combination is,
This parallel combination is in series is with 100 Ω.
Equivalent resistance is, Req = 18.75 + 100 = 118.75 Ω
When two liquids do not mix with each other to form a solution, what is it called?
For example- Alcohol and water.
Where has the second India-Myanmar bilateral Army exercise named 'IMBEX 2018-19' commenced on 14 January 2019?
Match List I with List II and select the correct answer using given options
Ohm’s Law: It states that Voltage across any conducting material is directly proportional to the current flowing through the material at a constant temperature. It gives the relation between voltage and current.
According to Ohm’s law, V = IR
Coulomb’s Law: It states that the magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.
An alternator is nothing but the AC generator that converts mechanical energy to electrical energy in the form of alternating current.
Internet Explorer is a __________.
Web browser: A browser is a software application used to locate, retrieve and display content of Web pages, images, video and other files. The browser contacts the Web server and requests information and Web server sends the information back to the Web browser which displays the results on the computer.
Some commonly used web browsers are:
In the following figure, for DC supply the resistance measured across A and B will be
At steady state, the capacitor acts as an open circuit.
Now, the circuit becomes
Equivalent resistance = 20 kΩ
Match List I with List II and select the correct answer from the given options:
Characteristics of Separately excited DC generator:
Characteristics of DC shunt generator:
Characteristics of DC series generator:
Characteristics of DC Compound generator:
The following comments can be made by above load characteristics of different generators.
The correct sequence of different layers of the atmosphere from the surface of the Earth upwards is
Structure of the atmosphere
The atmosphere is divided into five layers starting from the earth's surface:
The Exosphere is the uppermost layer of the atmosphere.
Which of the following is/are effects of ozone depletion?
Effects of ozone depletion
Alternators are constructed with:
The field winding of an alternator is placed on the rotor and is connected to DC supply through two slip rings.
The 3-phase armature winding is placed on the stator. This arrangement has the following advantages:
If the shunt capacitance is reduced then the string efficiency of an insulator is
The string efficiency is defined as the ratio of voltage across the string to the product of the number of strings and the voltage across the unit adjacent string.
String ef ficiency
Because of the shunt capacitance effect between insulators and tower, the voltage across each insulator is non-uniformly distributed.
If the shunt capacitance is reduced then the voltage across insulators will get uniformly distributed. Then string efficiency will increase.
The area of the hysteresis loop for a specimen is found to be large. This means that the hysteresis loss in this specimen would be _______
The energy loss associated with hysteresis is proportional to the area of the hysteresis loop. As the area of the hysteresis loop for a specimen is found to be large, the hysteresis loss in this specimen is also large.
Which among the following indicates the orientation of sub-shells in an atom?
In DC generator eddy current loss is nothing but:
As the armature core is made of iron and it rotates in a magnetic field, a small current gets induced in the core itself too. Due to this current, some losses occur in the armature iron core. These losses are called as Iron losses. These losses includes eddy current loss and hysteresis loss. Iron losses are also called as Core losses or magnetic losses.
In an Induction type meter, maximum torque is produced when the phase angle between two fluxes is
An induction type meter consists of two electromagnets, called shunt magnet and series magnet of laminated construction.
A coil having a large number of turns of fine wire is wound on the middle limb of shunt magnet. This coil is known as voltage coil or pressure coil and it is connected across the supply mains. It has many turns and is arranged to be as highly inductive as possible. This causes the current and therefore the flux, to lag the supply voltage by nearly 90°.
An adjustable copper shading rings are provided on the central limb of the shunt magnet to make the phase angle displacement between the magnetic field set up by shunt magnet and the supply voltage is approximately 90°.
The series electromagnet is energized by a coil which is known as current coil and it is connected in series with the load so that it carries the load current. The flux produced by this magnet proportional to and in phase with the load current.
The moving system essentially consists of a light rotating aluminium disk mounted on a vertical spindle or shaft. The fluxes produced by shunt and series magnet induce eddy currents in the aluminium disc. The interaction between these two magnetic fields and eddy currents set up a driving torque in the disc.
As in energy meter instrument, we have two fluxes and two eddy currents and therefore two torques are produced by
(i) First flux interacting with eddy current produced by second flux and
(ii) Second flux interacting with eddy currents generated by the first flux
Maximum torque is produced when the phase angle between these two fluxes is 90°
Which law of thermodynamics defines the concept temperature?
The Zeroth law of thermodynamics defines temperature. It states that “If two systems are in thermal equilibrium with the third system, then they are in thermal equilibrium with each other.”
Zeroth law – concept of temperature
First law – concept of internal energy
Second law – concept of entropy
What is peak factor of a sinusoidal wave?
Peak factor is defined as the ratio of peak value to rms value
Peak value of sinusoidal value = √2 × rms value
Peak factor of a sinusoidal value = √2 = 1.414
What is the SI unit of angular frequency?
The rotor of an induction motor cannot run at synchronous speed because:
Synchronous speed is the speed of rotation of the magnetic field in a rotary machine. An induction motor always runs at a speed less than synchronous speed.
The rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate. But due to the lagging of rotor flux current with respect to stator flux current, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed.
If the motor is running at synchronous speed, then the torque generated by the motor equal to zero. If rotor runs at synchronous speed as the field of the stator, this will cause the slip to become zero, then there will be no torque generated in rotor.
Which of the following statement is/are true?
Statement (S1): Conductivity of silicon is less than that of germanium at room temperature (300 K)
Statement (S2): As the temperature increases, the Fermi level of both N-type and P-type semiconductor materials moves towards the centre of the forbidden energy band gap.
Core is insulated by ________ in a belted cable:
Belted Cables: The conductors (usually three) are bunched together and then bounded with an insulating paper ‘belt’. In such cables, each conductor is insulated using paper impregnated with a suitable dielectric. The gaps between the conductors and the insulating paper belt are filled with a fibrous dielectric material such as Jute or Hessian.
The chemical formula of Hematite is ________.
In a single phase AC series motor the purpose of providing compensating winding is to:
The common causes of brush sparking in the universal motor (AC series motor) are:
Compensating winding is used to reduce sparking of brushes.
To calculate the power factor which of the following is odd one:
In AC circuits, the power factor is defined as the ratio of the real power flowing to the load to the apparent power in the circuit.
Hence power factor can be defined as watts to volt amperes
Power factor = cosϕ
Where, ϕ is the angle between voltage and current.
If current lags the voltage, power factor will be lagging.
If current leads the voltage, power factor will be leading.
From the options,
1) Ratio of real power to apparent power
2) P/VI represents the ratio of the real power to apparent power, it is known as power factor
3) R/Z also represents power factor from the impedance triangle
4) V/I represents resistance but not power factor
Which of the following prizes is given for fiction?
The Man Booker Prize for Fiction is a literary prize awarded each year for the best original novel written in the English language and published in the UK.
A voltage source having an open circuit voltage of 100 V and internal resistance of 50 ohms is equivalent to a current source of:
A voltage source having an open circuit voltage of 100 V and internal resistance of 50 ohms can be represented as 100 V voltage source in series with a resistance of 50 ohms as shown in the below figure.
By source transformation, we can represent this circuit as a current source with resistance in parallel.
Which of the following part of a transformer consists of a small vessel which contains a drying agent?
Whenever transformer is loaded, the temperature of the transformer insulating oil increases. Consequently, the volume of the oil is increased. As the volume of the oil is increased, the air above the oil level in conservator will come out. At low oil temperature, the volume of the oil is decreased, causes air to enter into conservator tank.
The air consists of moisture in it and this moisture can be mixed up with oil. Hence to filter the air from moisture silica gel breather is used. The drying agent extracts moisture from the in flowing air and ensures that only the dried air will be aspirated into the transformer.
An RLC series circuit is resonating at 150 Hz, its impedance at 50 Hz will be:
In series resonance,
The impedance - frequency curve is shown below
In the given question, resonant frequency (fr) = 150 Hz
Operating frequency (f) = 50 Hz
As operating frequency is less than the resonant frequency, impedance is capacitive.
Consider the following statements.
Statement A: Electricity is distributed from a single point in a radial distribution system
Statement B: There are less fluctuation in supply at the consumer’s terminal
Q. Which of the following is correct?
When the distributor is connected to a substation on one end only with the help of feeder, then the system is called a radial distribution system.
The feeders, distributors and service mains are radiating away from the substation hence name given as radial system.
There are combinations of one distributor and one feeder, connecting that distributor to the substation.
In the above diagram, one end of distributors are connected to the substation with the help of feeders and the other end will be connected to the service mains.
In this distribution system, electricity is distributed from a single point in a radial distribution system. The fluctuation in the supply is less at the consumer’s terminal.
Both the given statements are true, but B is not the correct explanation of A.
Find the value of the resistor R1 from the given circuit.
Given that, voltage across resistor R1 (VR1) = 6 V
Current flows through resistor R1 (IR1) = 4 A
Resistance (R1) = 6/4 = 1.5 Ω
With which game is the 'Agha Khan Cup' associated?
‘Agha Khan Cup’ is associated with the game of Hockey whereas Agha Khan Gold Cup is associated with Football.
The process of decomposing organic waste in the presence of air is termed as
Incineration is a waste treatment process that involves the combustion of organic substances contained in waste materials. Incineration and other high-temperature waste treatment systems are described as "thermal treatment". Incineration of waste materials converts the waste into ash, flue gas and heat means in the presence of air.
What is the IUPAC name of sec-Butyl chloride?
Which faults gives rise to symmetrical fault currents?
In symmetrical or balanced three-phase faults, all three phases are simultaneously short-circuited.
LLLG fault is a symmetrical fault. LG, LL, LLG faults are asymmetrical faults.
So, three-phase faults give symmetrical fault currents.
The shape of Indifference curve indicates ________.
An indifference curve is a graph showing combination of two goods that give the consumer equal satisfaction and utility. Each point on an indifference curve indicates that a consumer is indifferent between the two and all points give him the same utility.
Fundamental rights in the Indian constitution has been taken from which country's constitution?
1. Impeachment of the president
2. Functions of president and vice-president
3. Removal of Supreme Court and High court judges
4. Judicial review
5. Independence of judiciary
6. The preamble of the constitution
Which browser is an inbuilt browser in windows?
Some commonly used web browsers are:
The development of barrier potential in the depletion zone of a PN junction is consequent to:
Which one of the following is not a fractional horse power motor?
A fractional-horsepower motor (FHP) is an electric motor with a rated output power of 746 Watts or less.
There is no defined minimum output. However, it is generally accepted that a motor with a frame size of less than 35 mm square can be referred to as a micro-motor.
The synchronous motor is not a fractional horsepower motor.
Which among the following is the capital of Finland?
Helsinki is the capital of Finland.
A shaded pole induction motor does not have the advantage of
Shaded pole motor is used to drive the devices which require low starting torque. It has the following advantages.
EPROM stands for
The disease which is not caused by water pollution is
Asthma is a condition in which a person's airways become inflamed, narrow and swell and produce extra mucus, which makes it difficult to breathe. It is caused due to air pollution.
When is the World Earth Day celebrated?
Quality factor is defined as
Quality factor is defined as the ratio of the maximum energy stored to maximum energy dissipated in a cycle
In a series RLC, Quality factor
In a parallel RLC,
It is defined as, resistance to reactance of reactive element.
Which one of the following places of Indus Valley Civilization was situated on the bank of Ravi River?
Who has won the Men's singles final in the US Open Tennis 2018?
As a result of greenhouse effect, the average temperature of the earth’s atmosphere is gradually increasing. This is called _____.
As a result of the greenhouse effect, the average temperature of the earth’s atmosphere is gradually increasing. This is called Global warming. The exchange of incoming and outgoing radiation that warms the surface of Earth is known as the greenhouse effect. The greenhouse gases include carbon dioxide, methane, water vapors, nitrous oxide, and other gases.
Which of the following is not a greenhouse gas?
Green House Gases (GHG):
The major greenhouse gases are
So Ethane is not a greenhouse gas
Which of the following statements is true both for a series and a parallel D. C. circuit?
If two resistances are connected in parallel, they have the same potential difference across their ends but the current flowing through them will be different.
If two resistances are connected in series, the current flowing through them will be different, but they have different voltage drops across them.
Currents are additive in parallel circuits whereas voltages are additive in series circuits.
Powers are additive in both series and parallel.
Identify the incorrect statement/option: The psychological effect of noise pollution is
Noise pollution may cause or contribute to the following adverse effects:
The value of current I flowing in the 1 Ω resistor in the circuit shown will be
The voltage across 1 Ω resistor is 5 V
Current flows through 1 Ω resistor = 5/1 = 5 A
Material used in plate earthing are
In plate earthing, the earthing plate is placed deep into a pit (usually dug up to 2-3 meters), along with wood coal (absorbs and retains moisture) and salt (creates an ionic solution for faster dissipation of current). The plate is connected via a Copper conductor, or GI Conductor or concealed copper cable to the respective electrical set-up.
Damper winding and pony brake are the methods of starting of-
The synchronous motor is a constant speed motor and it always runs as at synchronous speed.
Due to the magnetic locking between stator and rotor poles synchronous motor is not self-starting and there is no starting device to accelerate the rotor to near synchronous speed.
It can be made self-starting by providing damper windings on rotor poles or by using pony motors.
Which of the following is NOT true with respect to Kirchhoff's first law?
Sewage waste is a
According to nature, pollutants can be classified into Non-degradable pollutants and Bio - degradable pollutants.
Those pollutants which cannot be broken down into simpler, harmless substances in nature.
DDT, plastics, polythene, bags, insecticides, pesticides, mercury, lead, arsenic, metal articles like aluminium cans, synthetic fibres, glass objects, iron products and silver foils are nonbiodegradable pollutants. (Tables)
Those pollutants which can be broken down into simpler, harmless substances in nature.
Sewage waste, domestic waste, etc. are the bio-degradable waste.
Which of the following is NOT a mouse usage?
A computer mouse is an input device that is most often used with a personal computer. Moving a mouse along a flat surface can move the on-screen cursor to different items on the screen. Items can be moved or selected by pressing the mouse buttons (called clicking). The mouse has two buttons, the left button, and right button, with a scroll wheel in between the two.
Use of a mouse:
Ward-Leonard control is basically a:
Ward-Leonard method of speed control is achieved by varying the applied voltage to the armature. Hence it is basically a voltage control method. The connection diagram is shown below.
In the above system, M is the main DC motor whose speed is to be controlled, and G is a separately excited DC generator. The generator G is driven by a 3-phase driving motor.
The voltage of the generator is changed by changing the generator field current. This voltage when directly applied to the armature of the main DC motor, the speed of the motor M changes.
Where is the largest population of Bhil Tribe found in India?
The Bhil are an indigenous tribe in the Kolarian group and were the earliest settlers in India. According to the 2011 Census of India, Bhil is the most populous tribe in Madhya Pradesh with a total population of 4,618,068, constituting 37.7 per cent of the total ST population.
The optical phenomenon that is primarily responsible for the observation of rainbow on a rainy day is ________.
Three resistors of 3 ohms, 10 ohms and 15 ohms are connected in parallel in a 30 V circuit. The current that will flow through the 3-ohm resistor is _________
As all three resistors are connected in parallel, the voltage across all the resistors will be the same.
Voltage across 3 ohm resistor = 30 V
Current flows through 3-ohm resistor = 30/3 = 10 A
The current in the circuit is
By applying KVL,
−36 + 4i0 + 5i0 = 0
⇒ i0 = 4A
In Fleming’s right hand rule, the middle finger indicates the direction of:
Fleming's Right-hand Rule shows the direction of induced current when a conductor attached to a circuit moves in a magnetic field. It can be used to determine the direction of current in a generator's windings.
As shown on the above figure, if the thumb, the forefinger, and the middle finger of the right hand are bent at right angles to one another with the thumb pointed in the direction of motion of a conductor relative to a magnetic field and the forefinger in the direction of the field, then the middle finger will point in the direction of the induced electromotive force.
Lenz's law: When a voltage is generated by a change in magnetic flux according to Faraday's law, the polarity of the induced voltage is such that it produces a current whose magnetic field opposes the change which produces it.
The voltage of a circuit is measured by a voltmeter whose input impedance is low as compared to the output impedance of the circuit. The error caused will be due to
When the voltage of a circuit is measured by a voltmeter whose input impedance is low as compared to the output impedance of the circuit, the instrument gives less accurate results. This is known as the error due to the loading effect.
To reduce this effect, we need to use high impedance voltmeter compared to the load impedance.
An ideal transformer does not-change:
An ideal transformer a transformer which has no copper losses, no iron loss in core and no leakage flux. In other words, an ideal transformer gives output power exactly equal to the input power.
Characteristics of an ideal transformer:
The total charge that has entered circuit element is q(t) = 0.50 (1 – e-5t) when t ≥ 0 and q(t) = 0 when t < 0. Determine the current in this circuit element for t ≥ 0
Given that, q(t) = 0.50 (1 – e-5t)
When a high reverse voltage is applied to a PN junctions:
The following image represents a section of a single bus scheme. The isolator is represented by which of the following?
In the given image,
An eddy current is a current ______
Eddy currents (also called Foucault currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.
Generation in computer terminology is
The generations of computers are characterized by a major technological development that fundamentally changed the way computers operate, resulting in smaller, cheaper, more powerful and more efficient and reliable devices.
The various generations of computers are listed below:
To measure insulation resistance of equipment’s of voltage rating up to 440 V the megger generator must generate
To measure insulation resistance of equipment’s of voltage rating up to 440 V the megger generator must generate the voltage more than the voltage rating of equipment. Hence the answer should be 500 V.
When warm air rises up and cold air from the surrounding areas rushes in to fill its place then this sets up ________ in air.
When warm air rises up and cold air from the surrounding areas rushes in to fill its place then this sets up convection in air.
What is the process of slow cooling of hot glass called?
A lamp of 100 W at 200 V is supplied current at 100 volts. It is equivalent to lamp of
Given that, Voltage (V1) = 200 V
Power (P1) = 100 W
Now it is connected to 100 V source.
The machine which works on dynamically induced emf is:
Dynamically induced emf:
Dynamic Induced emf is generated when a current carrying conductor cuts the magnetic flux using relative motion. It is having rotating parts in it, inducing emf with respect to moving parts is known as dynamic Induced emf.
Generator works on the production of dynamically induced e.m.f in the conductors.
Statically induced emf:
The emf is induced whenever a conductor is placed in the magnetic field of another conductor without having any relative motion. It doesn’t contain any moving part.
Transformer works on the production of statically induced e.m.f.
Which virus infects the important files of MS word?
A virus is a program that can infect other programs by modifying them to include a possibly evolved copy of itself.
Some of the common types of viruses are:
When a voltage is applied, the direction of electric field is always from _________ to _________.
The region around the electric charge in which the electric force act is called an electric field or electrostatic field.
If the magnitude of charge is large, then it may create a huge force around the region. The electric field is represented by the symbol E. The SI unit of the electric field is newton per coulomb which is equal to volts per meter.
Properties of an Electric Field:
For a D.C series motor, if Ta be the torque & Ia the armature current, then which relation is valid for the condition before saturation?
Torque is directly proportional to flux and armature current.
T ∝ ϕ Ia
In dc shunt motors, flux is constant. Hence torque is proportional to armature current.
T ∝ Ia
In dc series motors, flux is directly proportional to armature current. Hence torque is directly proportional to square of the armature current.
Ta ∝ Ia2
In dc series motor at saturation condition, flux is constant. Hence torque is proportional to armature current.
T ∝ Ia