RRB JE Electrical solved question paper 2014 | RRB JE Electrical

Answer.1. Holes

Explanation:-

The junction transistors are of two types: p-n-p transistor and n-p-n transistor. A transistor has the following sections:

 Emitter:- This forms the left-hand section or region of the transistor. The main function of this region is to supply majority charge carriers (either electrons or holes) to the base. Hence it is more heavily doped in comparison to other regions. Electrons are the charge carriers within the n-p-n transistor, whereas holes are the charge carriers within a p-n-p transistor.

Base:- The middle section of the transistor is called the base. This is very lightly doped and is very thin (10- 6 m) as compared to either emitter or collector so that it may pass most of the injected charge carriers to the collector.

Collector:- The right-hand side of the transistor is called the collector. The main function of the collector is to collect the majority charge carriers through the base. This is moderately doped.

The junction between the emitter and the base is called the emitter junction. The junction between the collector and the base is called the collector junction. In the normal operation of a transistor, the emitter-base junction is forward biased while the collector-base junction is reverse biased.

Working of P-N-P transistor

Fig. shows a P-N-P transistor connected in the common-base (or grounded-base) configuration (it is so-called because both the emitter and collector are returned to the base terminals). The emitter junction is forward-biased whereas the collector junction is reverse-biased. The holes in the emitter are repelled by the positive battery terminal towards the P-N or emitter junction. The potential barrier at the junction is reduced due to the forward bias, hence holes cross the junction and enter the N-type base. Because the base is thin and lightly doped, the majority of the holes (about 95%) are able to drift across the base without meeting electrons to combine with. The balance of 5% of holes is lost in the base region due to recombination with electrons. The holes which after crossing the N-P collector junction enter the collector region are swept up by the negative collector voltage V_c.

The following points are worth noting:

1. In a P-N-P transistor majority, charge carriers are holes.
2. The collector current is always less than the emitter current because some recombination of holes and electrons takes place. (I_C = I_E − I_B)

Answer.1. Pulsating

Explanation:-

Consider the case that the rotor of the single-phase induction motor is stationary and the stator is connected to a single-phase supply. When a single-phase supply is connected to the stator winding a pulsating or Alternating magnetic field is produced. This pulsating field builds up in one direction, falls to zero, and then builds up in the opposite direction. Under this condition, the resultant torque is zero and pulsating magnetic field cannot produce rotation in the rotor. Therefore, a single-phase induction motor is not a self-starting motor.

So if the rotor is ‘artificially’ started in one direction or the other, it will continue to rotate in that direction. This initial start is effected by adding a start winding, electrically a few degrees out-of-phase with the main stator winding. The field moves from the start winding to the main winding, and so the rotor receives a pulse start torque. The start winding is switched out of the circuit when the rotor is up to speed. The single-phase induction motor displays similar characteristics to those of the three-phase induction motor.

The pulsating torque results from the interactions of the opposite fluxes and m.m.f.’s which cross each other at twice the synchronous speed such as the interaction of the forward flux with the backward rotor m.m.f. and of the backward flux with the forward rotor m.m.f. The interaction of the forward flux with the rotor forward m.m.f. and that of the backward flux with the rotor backward m.m.f. produce a constant torque.

Note that the pulsating torque produces no average torque but rather produces a humming effect and makes single-phase motors noisier than polyphase motors.

Losses The alternation in field flux would cause excessive eddy current losses in the field core and yoke. The inductances of the field and armature windings cause abnormal voltage drops. So the torque developed is lower. 

Single-phase ac motors are employed for low-voltage, low-power applications -fractional-kW motors. They operate on the same basic principles as the 3-phase motor, but the pulsating single-phase field produces additional losses, reducing motor torque and the pulsating torque component increases the noise level of the motor. Therefore the capacity of the single-phase induction motor is limited by its pulsating torque hence the size of single-phase motors are limited to 5-hp.

Answer.4. All of these

Explanation:-

Lissajous Figures

Lissajous figures are a family of parametric 2D curves frequently used to establish the frequency ratio or relative phase between two harmonic signals. They were initially investigated by Nathaniel Bowditch in 1815,and later in more detail by Jules Antoine Lissajous in 1857.

The Lissajous pattern method is the quickest method of measuring the frequency. In this method, the standard known frequency signal is applied to horizontal plates and the simultaneously unknown frequency signal is applied to the vertical plates.

The shape of Lissajous figures depends on:

1. Amplitudes of two waves
2. The phase difference between two waves
3. The ratio of frequencies of two waves

If sinusoidal voltages are applied to both vertical and horizontal inputs of CRO, some interesting figures are displayed, which are known as Lissajous figures.

or

Lissajous figures are formed when two sine waves are applied simultaneously to the vertical and horizontal deflecting plates of a CRO.

Two sine waves of the same frequency produce a Lissajous figure which may be a straight line, an ellipse or a circle, depending on the phase and amplitude of the two signals.

Two sine waves of equal amplitudes but different frequencies will produce a figure from which the relationship between the two frequencies can be understood. For example, Fig.(a) shows that the vertical input signal has twice the frequency of the horizontal input signal. Similarly, Fig.(b) indicates that the horizontal input signal has twice the frequency of the vertical one. Fig.(c) shows three loops indicating that the vertical input signal has thrice the frequency of the horizontal one.

A known frequency (f_H) is applied to the horizontal input an unknown frequency (f_v) to the vertical input. Then a Lissajous pattern with loops is obtained. The unknown frequency (f_v) can be measured by the following relationship.

(f_v)/(f_H) =  No. of loops cut by horizontal line ⁄ No. of loops cut by a vertical line

Answer.2. Absolute zero temperature

Explanation:-

The average kinetic energy of the molecules of a gas is directly proportional to the temperature of the gas.

When the temperature of the gas increases, the kinetic energy of its molecules also increases. As the temperature of the gas decreases, the kinetic energy of its molecules decreases.

No gas can exist below -273°C. As the temperature decreases the volume also decreases and finally becomes zero at -273°C. This temperature at which the volume of gas becomes zero is caned Absolute zero (0K). Actually, the volume of gases cannot theoretically become zero as they liquify much before they reach this temperature.

Absolute zero is defined as that temperature at which the volume and pressure of a given mass of gas before zero.

Answer.4. All of the above

Explanation:-

A trivalent atom, the one that has three valence electrons is called an acceptor or recipient e.g, Boron(2, 3), Indium(2, 8, 18, 18, 3),  Aluminum(2, 8, 3), thallium(2, 8, 18, 32, 18, 3)

Answer.1. Square of the current

Explanation:-

According to the JOULE LAW OF HEATING

H = I²RT

Where

I = current

R = Resistance

T = Time

1. The amount of heat produced due to a current flowing through a conductor is directly proportional to the square of the current, provided the resistance of the conductor and the time for which the current is passed are constant. i.e. H ∝ I².
2. The amount of heat produced is directly proportional to the resistance of the conductor, provided the current and time remain constant. i.e. H ∝ R.
3. The amount of heat produced due to the current through a conductor is directly proportional to the time for which the current is passed, provided the current and resistance remain constant H ∝ R

Answer.1. −0.50 m/sec

Explanation:-

According to the conservation of Linear momentum

Mass of bullet × Velocity of bullet = Mass of gun × Velocity of recoiling 

or

M₁V₁ = −M₂V₂

The negative sign denotes the opposite direction

Given

Mass of bullet = 0.01 kg

Mass of gun = 5.0 kg

Velocity of bullet = 250m/sec

The velocity of recoiling  =?

V₂ = −M₁V₁/M₂

V₂ = −0.01 × 250/5 = −0.50m/s

Answer.1. u²/2g

Explanation:-

When motion takes place under gravity, the third equations of motion become

 v² = u² − 2gh(when the body is going upward)

Where

u = Initial velocity

v = final velocity

g = acceleration due to gravity

Here,

initial velocity = u

final velocity = 0 (at max. height, velocity is 0)

height covered = h 

∴ 0 = u² − 2gh

h = u²/2g

Answer.3. Particle accelerator

Explanation:-

The cyclotron is a device that is used to accelerate charged particles such as protons, deuterons, alpha particles, etc. to very high energies. The principle on which cyclotron works is based on the fact that an electric field can accelerate a charged particle and a magnetic field can throw it into a circular orbit. A particle of charge +q experiences a force qE in an electric field E and this force is independent of the velocity of the particle. The particle accelerated in the direction of the field. On the other hand, a magnetic field at right angles to the direction of motion of the particle throws the particle in a circular orbit in whit the particle revolves with a frequency.  If a charged particle is made to pass through this potential difference a number of times, will acquire an enormously large velocity and hens kinetic energy.

The energetic particles produced are used to bombard atomic nuclei and thereby produce nuclear reactions of interest to researchers.