RRB JE Electrical solved question paper 2015 | RRB JE Electrical

Answer.1. Cheapest critical activity

Explanation:-

Economic saving of time results by crashing the cheapest critical activity

Answer.2. 50.0%

Explanation:-

The relation between porosity of soil “η” and void ratio “e”

η = e/(1 + e)

Given void ratio  = 1

η = 1/2 = .5 or 50%

Answer.3. 45°

Explanation:-

Working Principle

The optical square belongs to reflecting instruments that measure angles by reflection. The working principle of an optical square may be stated as follows:

“If there are two plane mirrors whose reflecting surfaces make a given angle with each other, and if a ray of light in a plane perpendicular to the planes of both the mirrors is reflected successively from both, it undergoes a deviation of twice the angle between the reflecting surfaces”. In other words, the angle between the first incident ray and the last reflected ray is twice the angle between the two mirrors. In the case of the optical square, the angle between the two mirrors is 45°, while that between the first incident ray and the last reflected ray is 90°. 

Answer.4. Measurement of both horizontal and vertical angles

Explanation:-

The theodolite is the most accurate instrument used mainly for measuring horizontal and vertical angles. It can also be used for locating points on a line, prolonging survey lines, finding the difference in elevations setting out grades ranging curves, etc.

Answer.3. Bernoulli’s principle

Explanation:-

Bernoulli’s principle can be derived from the principle of conservation of energy. This states that in a steady flow the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass. The sum of pressure and gravitational potential ) is the same everywhere.

Applications of Bernoulli’s Principle

Dynamic lift:-

Wings of an airplane: The wings of the airplane are having tapering. In an airplane, the top of the wing is somewhat curved while the bottom of the wing is flat. Due to this specific shape of wings when the airplane runs, air passes at a higher speed over it as compared to its lower surface. This difference of airspeeds above and below the wings, in accordance with Bernoulli’s principle, creates a pressure difference, due to which an upward force called ‘dynamic lift’ (= pressure difference area of the wing) acts on the plane. If this force becomes greater than the weight of the plane, the plane will rise up.

Answer.2. Sulphuric acid

Explanation:-

Concrete has good resistance to attack by dry chemicals, dry soils containing chemicals, most alkalies, mineral oils, neutral salts, and many salts, of strong bases, although it is susceptible to varying degrees of attack by another chemical.  These include acid-producing substances, ammonia salts, magnesium salts, concentrated solutions of strong bases such as NaOH, chlorides, sulfates, nitrates, salts of weak bases, animal wastes, sewage water, sulphuric acid vegetable, and animal oils, fats, sugar, glycol, glycerol, phenol, and creosote.

Answer.2. 0.5

Explanation:-

As given in the above question

W₁ = 1700 W

W₂ = 1100 W

The power factor of the two wattmeters is

tanØ =  √3[(W₁ – 0) / (W₁ +0)]

tanØ = √3

Φ = 60°

Power factor = cosφ = cos60° = 0.5

Answer.4. X-Y plates

Explanation:-

Cathode Ray Oscilloscope

CRO is an electronic instrument used for measuring voltage, time, frequency, phase shifts and for observing the shape of the input waveform. It is also known as a fast x-y plotter which displays an input signal versus another signal or versus time. The heart of CRO is CRT, i.e. cathode ray tube as shown in Fig.

Construction and operation of CRT

The cathode ray tube (CRT) can be divided into three parts,

1. Electron gun assembly
2. Deflection plates
3. Screen.

The electron gun assembly consists of a heater, cathode, control grid, focussing anode and accelerating anode. The cathode emits electrons. A negative voltage is applied to the control grid so that it controls the number of electrons emitted from the cathode. In this way, the intensity of a beam can be controlled by controlling the negative voltage applied to the grid. The sharpness of the beam is controlled by potential applied to the focusing anode and the beam is accelerated by the high positive voltage applied to the accelerating anode.

Now the focussed and accelerated electron beam is passed through the vertical and horizontal deflection plates. A voltage is applied to the horizontal plates to deflect the beam in the ‘x’ direction while the voltage is applied to vertical plates in order to deflect the beam in the ‘y’ direction. But the simultaneous force exerted in the x and y directions deflects the beam in such a way that a waveform is displayed on the screen. Now, the focus accelerated, and deflected beam strikes the screen. The screen is coated with phosphorous material which converts the electrical energy into light. All the working parts of CRT are enclosed in an evacuated glass envelope. The electrons striking the screen release secondary electrons. These secondary electrons are collected by Aquadag which is connected to the second anode, the collection of secondary electrons is required to keep the CRT screen in an electrical equilibrium state.

Hence from the above discussion, it is clear that the X-Y plate is not part of an electron gun.

Answer.1. Voltage

Explanation:-

The strain is defined as the deformation of materials caused by the action of stress. Strain can be determined by measuring the fractional change in the length of a particular body. The strain gauge accomplishes this by changing its resistance in response to very small changes in length. The voltage output by the gauge will vary depending upon the amount of deformation the body it is attached to has undergone. 

A strain gage is a circuit that produces a voltage that is proportional to the amount of strain that is applied to the gage. Typically, the gauge will produce a linear output over some specified interval of strain.

Answer.3. It does not load the circuit at all

Explanation:-

A null method of measurement is a simple, accurate, and widely used method that depends on an instrument reading being adjusted to read zero current only. The measurement process is to reduce the difference between a known and an unknown quantity to zero, that is, a null would be indicated. The method assumes:

(i) If there is any deflection at all, then some current is flowing;

(ii) If there is no deflection, then no current flows (i.e. a null condition).

The potentiometer method is a null method. At the null point, no current flows in the circuit under measurement. Hence, the potentiometer measures the exact p.d. On the other hand, when a voltmeter is connected to measure p.d. across a component (say a resistor), a part of the current is drawn by the voltmeter. As a result, the current through the component decreases. Hence, p.d. being measured by the voltmeter is slightly less than the actual value.