RRB JE (Railways Junior Engineer) CBT EE CBT 2 Full Test 2 Free Online

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

In transformers, voltage transformation ratio is the ratio of secondary induced emf to primary induced emf.

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
X_L is inductive reactance
X_{C­ ­}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.

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

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.

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.

• The internet is a globally connected network system that transmits data via various types of media; Sometimes it is referred to as a ‘network of networks’
• The World Wide Web, or simply web, is a way of accessing information over the medium of the internet
• A web browser is a software application for accessing information on the World Wide Web

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 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.

We can directly measure voltage, current and frequency by using CRO. We cannot directly measure power by using CRO.

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).

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

• When acid rain falls and flows as groundwater to reach rivers, lakes etc, it affects plants and animal life in the aquatic ecosystem
• Acid rain is harmful to agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth
• It causes respiratory ailments in human beings and animal
• It may also cause corrosion in many buildings bridges, monuments, fencing etc
• It causes irritation in the eyes and skin of human beings
• This rain reduces the lustre of the metals too
• Acid rain damages buildings and other structures made of stone or metal
• The Taj Mahal in India has been affected by acid rain

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.

• Motors with low starting torque have the capacitor left in circuit all the time
• Motors with higher starting torque might need a bigger capacitor, and that will have a centrifugal switch to disconnect it once the motor is running

Shaded pole motor is used to drive the devices which require low starting torque. It doesn’t have any centrifugal switch.

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.

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:

• The oil has high dielectric strength and provides insulation between the contacts after the arc has been extinguished
• Oil provides a small clearance between the conductors and the earth components
• The hydrogen gas is formed in the tank which has a high diffusion rate and good cooling properties

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.

Ideal voltage source: An ideal voltage source have zero internal resistance.

Practical voltage source: A practical voltage source consists of an ideal voltage source (V_S) in series with internal resistance (R_S) 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.

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.

• They do not deteriorate with time
• They have inverse time-current characteristics
• Operation of the fuse is very reliable
• It is required to be replaced after each operation

• Light can travel in a vacuum because the light is electromagnetic in nature which requires no medium as electric fields and magnetic fields constantly generate each other as the wave propagates.
• Sound waves require a medium to travel. The speed of sound is faster in solid materials, slower in liquids and slowest in gases.
• The speed of light in a vacuum is commonly given the symbol c. It is a universal constant that has the value c = 3 x 10⁸ m/second.

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 is a narrow stretch of water which separates the Malay Peninsula and Indonesian Island of Sumatra.
• It was named after the Malacca Sultanate which ruled between 1400 and 1511 over a group of islands.

• A transistor is a device that regulates current or voltage flow and acts as a switch or gate for electronic signals
• It is low voltage and low current device because semiconductors are sensitive to high voltages and current and can be easily destroyed

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%.

The mutual inductance between two magnetically coupled coils is given by

Where μ_r 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.

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.

• Vice Admiral G Ashok Kumar, AVSM, VSM assumed charge as Vice Chief of the Naval Staff on 30 Jan 2019.
• Kumar has held various Staff and Command assignments during his distinguished naval career spread over more than three decades.
• He is an alumnus of National Defence Academy, Khadakvasla, Pune and was commissioned into the Executive Branch of the Indian Navy on 01 Jul 1982.

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:

• Malware: A collective term for malicious software, such as viruses, worms and trojans; designed to infiltrate systems and information for criminal, commercial or destructive purposes.
• Phishing: A form of social engineering, involving the sending of legitimate-looking emails aimed at fraudulently extracting sensitive information from recipients, usually to gain access to systems or for identity theft.
• Spam: Unsolicited email sent in bulk to many individuals, usually for commercial gain, but increasingly for spreading malware.

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.