RRB JE Electrical solved question paper 2014 | RRB JE Electrical

RRB JE Electrical solved question paper


Ques.1. Cores of an electric motor are generally made from a lamination of:

  1. Carbon
  2. Silicon Steel
  3. Cast iron
  4. None of the above

Answer.2. Silicon Steel


The cores of an electric motor are generally made from a lamination of Silicon Steel.

An electric motor consists of mainly two parts

  1. Stator
  2. Rotor


The stator core is the part containing the main magnetic flux circuit of machines and the place where to lay in the stator winding. In order to reduce the eddy current loss and magnetic hysteresis loss caused by a rotating magnetic field in the iron core, the stator core is formed by a lamination of 0.5 mm thick silicon steel sheet, with varnish coated on both sides of the silicon steel sheet to ensure insulating. 

These laminations are insulated from one another by a coating of varnish and stacked together. Radical ventilating ducts are provided at intervals of about 8 cm along the axial length of the stator so as to improve the circulation of cooling air.


The rotor is composed of a core, the winding, and a turning shaft, and the rotor core is also a part of the magnetic circuit of the motors. The rotor is also subjected to a rotating magnetic field though of lesser frequency. Hence, the rotor is built up of laminations of higher thickness than those of the stator. Ventilating ducts are provided in the same positions on its axial length as the stator. 


Ques.2. For which of the following application, a D.C motor is preferred over an A.C Motor?

  1. Variable speed operation
  2. High-speed operation
  3. Low-speed operation
  4. Fixed speed operation

Answer.1. Variable speed operation



Variable speed operation:- The attractive feature of the dc motor is that it offers a wide range of speed control both above and below the rated speeds. This can be achieved in dc shunt motors by methods such as the armature control method and field control method. This is one of the main applications in which dc motors are widely used in fine speed applications such as in rolling mills and in paper mills.

High starting torque: D.C series motors are termed as best suited drives for electrical traction applications used for driving heavy loads in starting conditions. DC series motors will have a starting torque as high as 500% compared to normal operating torque. Therefore dc series motors are used in the applications such as electric trains and cranes.

Accurate steep less speed with constant torque: Constant torque drive is one such drive that will have motor shaft torque constant over a given speed range. In such drives, shag power varies with speed. Quick starting, stopping, reversing and acceleration.

Free from harmonics, reactive power consumption, and many factors which make dc motors more advantageous compared to ac induction motors.


Ques.3. The dynamic resistance of a diode is defined as

  1. The ratio of small change in voltage to a small change in current
  2. The ratio of small change in voltage to the square of the small change in current
  3. The ratio of applied voltage to current
  4. None of the above

Answer.1. The ratio of small change in voltage to a small change in current


When a diode uses an A.C signal, and when the input variation is very small, the signal is referred to as a small signal. Within the small limit of use, in the small portion of the V-l characteristic, even though the total characteristic is nonlinear, it is assumed that the device is linear and analysis is performed. To determine the resistance offered within this small region of operation, static resistance is not going to give complete behavior of the diode. Thus, a resistance known as dynamic resistance is useful.

Dynamic resistance is the ratio of a small change in voltage to the corresponding change in the current. Thus,

r = dv/di


Ques.4. One meter is equal to

  1. 10−6 micron
  2. 106 micron
  3. 10−3 micron
  4. 103 micron

Answer.2. 106


1 meter is equal to 1000000 micrometer

1 meter = 106 micron


Ques.5. With the addition of impurities the resistance of the semiconductor

  1. Increases
  2. Decreases
  3. First increase then decrease
  4. First decrease then increase

Answer.2. Decreases


Impurity Level in n-type Semiconduction: In an n-type semiconductor the impurity level appears close to the conduction band and therefore, at ordinary temperature electrons can easily move from the impurity level to the conduction band and this thing contributes highly towards electrical conductivity.

Impurity Level in p-type Semiconductor: In a p-type semiconductor, the impurity level appears close to the valence band. Therefore at ordinary temperature electrons acquire enough energy to move easily from the top of the valence band to the impurity level and leave positive holes in the valence band which is free to move within the semiconductor and this thing contributes highly toward conductivity.

impurity level

It is clear, therefore, that the addition of donor or acceptor impurity increases the conductivity above the intrinsic level of the semiconductor. In n-type material the majority carriers are electrons and minority carriers are holes while in the case of p-type material the situation is reversed.


Ques.6. Creeping occurs in:-

  1. Ammeter
  2. Energy Meter
  3. Voltmeter
  4. None of these

Answer.2. Energy Meter


Creeping in the energy meter is the phenomenon in which the aluminum disc rotates continuously when only the voltage is supplied to the pressure coil, and no current flows through the current coil. In other words, the creeping is the kind of error in which the energy meter consumes a very small amount of energy even when no load is attached to the meter.

Creeping occurs due to

  1. Overcompensation for friction.
  2. Supply voltage is more than normal voltage
  3. Stray magnetic field
  4. Vibration

To eliminate this, two holes are drilled in the disc 180° opposite to each other. When this hole comes under the shunt magnet pole, it gets acted upon by a torque opposite to its rotation. This restricts its rotation, on no-load condition.


Ques.7. The term RADAR stands for

  1. Radio direction and reflection
  2. Radio detection and ranging
  3. Radio waves dispatching and receiving
  4. Random Dispatching and receiving

Answer.2. Radio detection and ranging


Radar stands for Radio Detection and Ranging. Radars use the electromagnetic spectrum for transmitting and receiving signals.


Ques.8. Which of the following is an active component of the circuit?

  1. Transistor
  2. Resistor
  3. Capacitor
  4. Inductor

Answer.1. Transistor


Components that require an external source of power, and/or produce again in a circuit, are called active component


An active network transfers energy from an external source to an output signal, which may be generated within the network (as in an oscillator) or is controlled by an input signal. such as a transistor, amplifier, oscillator


Ques.9. A transistor has an emitter current of 8mA and α of 0.99. Which of the following could be the collector current?

  1. 7.92 mA
  2. 5.00 mA
  3. 81 mA
  4. 7.84 mA

Answer.1. 7.92 mA


D.C current gain α can be expressed as

α = IC/IE


IC = collector current

IE = Emitter current


α = 0.99

IE = 8mA

IC = α × IE

IC = 7.92 mA


Ques.10. An accurate ammeter must have a resistance of

  1. High value
  2. Low value
  3. Very low value
  4. Very high value

Answer.3. Very low value


An ammeter is connected in series with the load and to measure current, you want most of the current to pass through it. Hence ammeter is connected in series with the low resistance

An ammeter measures the value of current flowing in the circuit, so the current should flow inside the ammeter to give proper results. it acts like a closed switch so it indicates the current. And it has very low resistance to ensure the correct measurement of current in the circuit. If it is connected in parallel across any load then all current in the circuit will choose the lower resistive path (i.e ammeter) to cause its circuit to be damaged. Hence it is used in series.

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