RRB JE Electrical Solved Question paper 2012 | RRB JE Electrical

Ques.61. If a transformer is fed from a D.C rather than a 1-phase A.C supply, then the transformer will

  1. Burn its winding
  2. Operate Normal
  3. Will not operate
  4. Will give very small leakage flux

Answer.1. Burn its winding

Explanation:-

If the primary of a transformer is connected to a d.c. supply, the primary will draw a steady current and hence produce constant flux. Consequently, no back e.m.f. will be produced. The primary winding will draw excessive current due to low resistance of the primary. The result is that the primary will overheat and burn out or the fuses will blow. Care must be taken not to connect the primary of a transformer across the d.c. supply.

 

Ques.62. If a pure inductor is connected across the AC source the average power taken by the inductor is

  1. A few watts
  2. 100 watt
  3. 0 watt
  4. Maximum power

Answer.3. 0 watt

Explanation:-

In the purely inductive circuit the current lag behind the voltage by 90°.

average power in inductor

Let us see what really takes place in a purely inductive circuit. During the one-quarter cycle of an alternating source of e.m.f., energy is stored in the magnetic field of the inductor. This energy is supplied by the source. During (the next quarter cycle, tile stored energy is returned to the source. For this reason, the average power absorbed by a pure inductor over a complete cycle is zero.

 

Ques.63. Output of a welding transformer, compared with its input is

  1. High voltage high current
  2. High voltage low current
  3. Low voltage high current
  4. Low voltage low current

Answer.3. Low voltage high current

Explanation:-

A welding power supply is a device that provides an electric current to perform welding. Welding usually requires a high current (over 80 amperes) and it can need above 12,000 amperes in spot welding.

A welding transformer is a step down electrical transformer that converts the moderate voltage and moderate current electricity from the utility mains (typically 230 or 115 VAC) into a high current and low voltage supply, typically between 17 and 45 (open-circuit) volts and 55 to 590 amperes

 

Ques.64. In a mercury arc rectifier, mercury is used as

  1. Cathode
  2. Conducting medium
  3. Anode
  4. Electrons accelerator

Answer.2. Conducting medium

Explanation:-

Similar to a common diode, a mercury arc rectifier consists of a cathode and an anode. Mercury is used as the cathode and the anode is made of iron.

When the rectifier is in operation, mercury forms an arc between the mercury surface and the iron anode. This arc contains ionized mercury vapor consisting of electrons and positive ions. The area on the surface of the mercury where the arc concentrates is known as the cathode spot. This is a region of high temperature and most of the ionization (formation of irons by the loss of electrons), takes place here. In the arc, the electrons are attracted by the positive anode whereas positive ions are attracted by the negative cathode. Since the positive ions are heavy, they carry a lot of kinetic energy which is released in the Bonn of heat energy when they strike the cathode.

MERCURY ARC RECTIFIER

A part of or all the mercury vaporizes and the vapor atoms ionize and serve as the conducting medium in the tube. Hence the mercury vapor may be used as the conducting medium in a diode of the gas-filled type and is widely used in heavy-duty rectifiers. Just as in other types of diodes, the cathode of the mercury-vapor rectifier must be heated before conduction can take place. The use of mercury as the cathode permits the rectifier to withstand heavy momentary overloads without damage. The heat of the arc produces the necessary ionization of the mercury vapor, and conduction takes place through the external anode circuit if complete. 

 

Ques.65. The radiation present in sunlight which makes a solar cooker work is

  1. Visible light rays
  2. Ultraviolet rays
  3. Cosmic rays
  4. Infrared rays

Answer.4. Infrared rays

Explanation:-

A solar cooker is a device used for cooking food using solar energy. It is a box type of structure made of non-conducting materials like either plastic or fiberglass.

When a box covered with a glass sheet is placed in the sun, visible light as well as infrared radiations pass through the glass sheet and enter in the box. As the inner surfaces of the box are painted black, most of the radiations are absorbed by the walls of the box and as a result, walls become quite hot. Due to temperature rise, these walls start radiating heat in the form of infrared rays of much longer wavelengths. Glass sheet has a peculiar property that it allows lower wavelength infrared to pass through it but does not allow longer wavelength infrared to escape, as a result, the heat is trapped inside the box. The trapping of heat is called the greenhouse effect. 

solar cooker

 

RRB Reasoning, Aptitude and G.K

 

Ques.66. Which organization has proposed first to constitute the Constitution Assembly to form the Indian constitution?

  1. Sawaraj party in 1928
  2. Indian National Congress in 1936
  3. Muslim league in 1942
  4. By all parties convention in 1946

Answer.2. Indian National congress in 1936

Explanation:-

Ques.67. There are rings around which of the following planets?

  1. Uranus
  2. Mars
  3. Jupiter
  4. Saturn

Answer.4. Saturn

Ques.68. Where is the headquarter of the Geological Survey of India located?

  1. Patna
  2. Dehradun
  3. Kolkata
  4. Agra

Answer.3. Kolkata

Ques.69. Nasik is siutated on the bank of which river?

  1. Godavari
  2. Narmada
  3. Tapti
  4. Shipra

Answer.1. Godavari

 

Ques.70. Who started the Shaka era?

  1. Ashoka
  2. Chandragupta-II
  3. Kanishka
  4. Harsha

Answer.3. Kanishka

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