RRB JE Electrical (CBT II) Mock Test- 1 - Electrical Engineering (EE) MCQ

v = 800Hz, λ = 0.5 m
v = nλ = 800 x 0.5 = 400m/s
Time = 400/400 = 1sec

A single phase motor has two windings: main winding and auxiliary winding. These both windings are placed on stator. Motor has a centrifugal switch inside its case, attached to the motor shaft.

The centrifugal switch turns on a circuit, providing the needed boost to start the motor. Once the motor comes up to its operating speed, the switch turns off (disconnects auxiliary winding) the boost circuit, and the motor runs normally.

Given resistor is a active element.
Given that, I = 2V².
Given V-I characteristic represents non-linear relation between current and voltage.

A pressure transducer is used to convert a certain value of pressure into its corresponding mechanical or electrical output.

The transducers used for static pressure measurement are

Semi-conductor strain gauge

Variable capacitor for transducer

Piezoelectric transducer

Metal wire strain gauge is least suitable for static pressure measurement.

• 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

Peak factor is defined as the ratio of peak value to rms value

Peak value of sinusoidal value = √2 × rms value

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

Reluctance opposes the passage of magnetic flux lines. Reluctance is analogous to resistance.
We can define the reluctance as,
R = mmf/0
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
ø = BA
= μHA

Now, we can define reluctance as

• Scanner scans any document and sends it to computer, so it is a input device.
• Speaker gets data from computer in form of audio. So it is a output device.
• Plotter is printer that print vector image. It recieve data from computer and print it on paper. So it is also a output device.

• Methane and Carbon dioxide are the main constituent of Biogas.
• Methane is produced by the anaerobic bacterial decomposition of vegetable matter under water.
• It is also known as marsh gas or swamp gas.
• Its chemical formula is CH_4.

In transformers, voltage transformation ratio is the ratio of secondary induced emf to primary induced emf.
K = E₂/E₁ = N₂/N₁ = I₁/I₂

As compared to all motor, a capacitor start motor has higher starting torque because capacitor start motors employs a capacitor in the auxiliary winding circuit to produce a greater phase difference between the current in the main and the auxiliary windings.

The order of starting torque in the increasing order is: Shaded-pole motor < Split phase motor < Capacitor start capacitor run motor < Capacitor start motor

Current sensitivity: The current sensitivity of a galvanometer is defined as the deflection produced by unit current.
Current sensitivity Si = G/500K mm/ μ A
Where G = NBA is a displacement constant and
K is a control constant
N = number of turns
B = flux density
A = Area
Voltage sensitivity: The voltage sensitivity is the deflection in scale divisions per unit voltage impressed on the galvanometer.
Voltage sensitivity S_v = G/500KR_g mm/ μV
Where R_g­ resistance of coil
Method to increase sensitivity:
The current sensitivity can be increased by increasing the number of turns, using high flux density and by increasing the dimensions of coil.
For a given coil area (A) and a constant value of flux density (B), the displacement constant (G) can be increased by increasing the number of turns.
If the winding area is fixed, a large number of turns can only be wound by using a thin wire. Thus, we can increase the sensitivity of a galvanometer by winding its coil with large number of turns of thin fine wire.
However, this increases the resistance of the coil (Rg) also as resistance is proportional to length of conductor).
As voltage sensitivity depends on resistance of the coil, we need to consider the two effects i.e. increase in the value of displacement constant (G) and increase in the resistance (Rg).
So, current sensitivity is increasing but the voltage sensitivity may increase or decrease.

Drawbacks of electric traction system:

• Electric traction system involves high erection cost of power system
• Interference causes to the communication lines due to the overhead distribution networks
• The failure of power supply brings whole traction system to stand still
• In an electric traction system, the electrically operated vehicles must move only on the electrified routes
• Additional equipment should be needed for the provision of regenerative braking, it will increase the overall cost of installation

• Due to a small area of hysteresis loop and small residual magnetism steel sheet is used for transformers, AC machines etc.
• Materials with a large hysteresis loop are used for producing permanent magnets
• Such a hysteresis loop represents a large residual flux and hence a large coercive force
• Hence materials such as the hard steel with some tungsten, cobalt or chromium are used for such an application

We know that

Here P = number of pole, N = Speed, f = frequency

• If N is the speed, then the windage loss in dc motor is proportional to square of armature speed
• Windage losses occur due to the air inside the rotating coil of the machine
• Eddy current losses are proportional to square of speed.

• A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions.
• RAM and cache are example of primary storage. Cache is a part of central processing unit.

• The first amendment to the Indian Constitution added the Ninth Schedule to it in 1951.
• It ensured that the laws related to land reforms were not challenged in courts for violation of fundamental rights.

Concept:
The reaction of Zn and HCl is example of displacement reaction.
When a more reactive element displaces a less reactive element from its compound then that is known as displacement reaction. Both metals and nonmetals take part in displacement reactions
Application:
The underlying reaction between hydrochloric acid and granulated zinc is :
Zn + 2HCl → ZnCl₂ + H₂
From the above reaction the gas released is H₂
H₂ is colourless odourless gas which burns with a popping sound.

Two 100 Ω resistors are connected in parallel
R_100║100 = 100 x100/200 =  50 Ω

R_AB = 100 + 50 = 150 Ω

Two in parallel and one in series combinations is the best for replacing a 150 Ω resistor in a circuit using 100 Ω in the laboratory.

A parallel combination of two 2 ohms resistance gives
R’ = 2 || 2 = 1 Ω

Connecting this combination in series with 2 Ω resistance gives
R_eq = R’+ 2 = 1 + 2 = 3
Hence, A parallel combination of two resistance (which will be 1 ohm) joined in series with the third resistance (2 ohm)

• Reluctance start motor is a type of synchronous motor.
• The reluctance motor has basically two main parts called stator and rotor.
• The stator has a laminated construction, made up of stampings.
• The stampings are slotted on its periphery to carry the winding called stator winding.
• The stator carries only one winding and it is excited by single-phase AC supply.
• The rotor has a particular shape. Due to its shape, the air gap between stator and rotor is not uniform.
• Its working principle is similar to a shaded pole motor.

Linear Elements: A linear element is one whose parameters do not change with voltage or current. It has primarily two properties: homogeneity and additivity.

Example: Resistor, Inductor, Capacitor

Nonlinear Elements: A nonlinear element is that whose parameters change with voltage or current. It does not obey homogeneity and additive properties.

Example: Diode, Transistor

Magnification of a lens is defined as the ratio of the height of the image to the height of the object.
m = h/[?]
h' = Height of the image
h = Height of the object

The capacitor motor develops relatively poor starting torque when compared to universal motor and repulsion motor. To obtain a high starting torque, the two conditions are essential.

• The starting capacitor value must be large
• The value of the starting winding resistance must be low

Important Point:

• The electrolytic capacitors of the order of the 250 µF are used in capacitor motors because of the high Var rating of the capacitor requirement
• Universal motors are generally series wound (armature and field winding are in series), and hence produce high starting torque
• Universal motors find their use in various home appliances like vacuum cleaners, drink and food mixers, domestic sewing machine, etc.
• The higher rating universal motors are used in portable drills, blenders, etc.
• Repulsion motor is used for loads requiring high starting torque such as hoists, lifts, etc.