RRB JE Electrical (CBT II) Mock Test- 10 - Electrical Engineering (EE) MCQ

The induced emf when a conductor cuts the magnetic field is

e = Bil sinθ

B is magnetic flux density

i is the current flowing through the conductor

l is the length of the conductor

θ is the angle

Induced emf is maximum at θ equals to 90 degrees.

The wattage rating for a ceiling fan motor is in the range of 50 to 150 W. Fans range in size from 36 inches to 56 inches use 55 to 100 watts, a typical 48 inch ceiling fan will use 75 watts.

A fractional-horsepower motor (FHP) is an electric motor with a rated output power of 1 HP (746.9 or 746 Watts) or less.

Single phase induction motors have very less rating hence these are also known as fractional horsepower motors.

Spot welding means the joining of two metal sheets and fusing them together between copper electrode tips at suitably spaced intervals by means of heavy electric current passed through the electrodes.

In this type of welding, the composition and thickness of the base metal determines:

Holding time

The amount of weld current

The amount of squeeze pressure

A single phase motor cannot create a rotating magnetic field. It will just standstill and oscillate. To see this disconnect the start winding and you will see the motor will not start up. If you twist motor shaft with fingers it will run in whichever direction you twist. To self start a single phase motor one must create a rotating magnetic field on the stator. Two windings are used and the difference in impedance creates a phase delay in the magnetic fields produced by each winding allowing the motor to start.

number of branches of root locus tends towards infinity is equal to
= P - Z
P = number of poles of open loop system
Z = number of zero of open loop system.
in given problem P = Z then branches toward infinity is zero.

In forward blocking mode junction J 2 and in reverse blocking mode junction J 1 and J 3 acts as capacitor hence leakage current present in both direction.

• A transistor is a device that regulates current or voltage flow and acts as a switch or gate for electronic signals
• It is low voltage and low current device because semiconductors are sensitive to high voltages and current and can be easily destroyed

When the distributor is connected to a substation on one end only with the help of feeder, then the system is called a radial distribution system.

The feeders, distributors and service mains are radiating away from the substation hence name given as radial system.

There are combinations of one distributor and one feeder, connecting that distributor to the substation.

In the above diagram, one end of distributors are connected to the substation with the help of feeders and the other end will be connected to the service mains.

In this distribution system, electricity is distributed from a single point in a radial distribution system. The fluctuation in the supply is less at the consumer’s terminal.

Both the given statements are true, but B is not the correct explanation of A.

The string efficiency is defined as the ratio of voltage across the string to the product of the number of strings and the voltage across the unit adjacent string.

Because of the shunt capacitance effect between insulators and tower, the voltage across each insulator is non-uniformly distributed.
If the shunt capacitance is reduced then the voltage across insulators will get uniformly distributed. Then string efficiency will increase.

Electric shock occurs upon contact of a (human) body part with any source of electricity that causes a sufficient magnitude of current to pass through the human body.

The current through the source can be calculated using current division:
 I_L = I (R_s/R_s + R_L)
I_L = 16 (10/10 +2.5) = 160/12.5 m A

• The transformer which changes the magnitude and phase angle at a certain point in the power system is known as the regulating transformer
• It is mainly used for controlling the magnitude of the bus voltage and for controlling the power flow, which is controlled by the phase angle of the transformer
• Hence these are used to control the load flow
• The regulating transformer is of two types; One is used for changing the magnitude of voltage which is called online tap changing transformer and the other is called phase shifting transformer

The equivalent resistance in the circuit is,
 Req = 10 + (15║15║ R) 
= 10 + (7.5 ║R) 
= 10 + 7.5R/7.5 + R
Given that, current flowing though the circuit (I) = 3 A
We know that, V = IR_eq
⇒ 40 = 3 (10 + 7.5R/7.5 + R ) 
⇒ 10/3 = 7.5R/7.5 + R
⇒ 75 + 10R = 22.5R
⇒ 12.5R = 75 ⇒ R = 6 Ω

• When a high voltage is applied across an air gap, the air in the gap gets ionized under the influence of electrostatic forces and becomes conducting medium.
• Current flows in the form of a continuous spark, called the arc.
• It is to be noted that a very high voltage is required to establish an arc across an air gap but to maintain an arc small voltage may be sufficient.

Wattmeter reading in two wattmeter method are,
W₁ = V_LI_L cos (30 - ϕ)
W₂ = V_LI_L cos (30 + ϕ)
The active power will be = W₁ + W₂ = 8.2 + 7.5 = 15.7 W
Important:
tan Ø√ 3 ( W₁ - W₂)/( W₁  + W₂)
Power factor = cos ϕ

Potential difference = 0.5 V
I = 4 A
R = ?
R = V/I
V stands for potential difference
R = 0.5/4
R = 1/8
R = 0.125 Ω

• 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

The order of waste management hierarchy, from most to least favoured is:
Prevention-Reuse-Recycle-Recovery-Disposal

Prevention: Preventing and reducing waste generation.
Reuse: Giving the products a second life before they become waste.
Recycle: Any recovery operation by which waste materials are reprocessed into products, materials or substances whether for the original or other purposes
Recovery: Some waste incineration based on a political non-scientific formula that upgrades the less inefficient incinerators.
Disposal: Different processes to dispose of the waste are landfilling, incineration, pyrolysis, gasification and other finalist solutions.

AC series motors are also known as the modified DC series motor as their construction is very similar to that of the DC series motor. If a DC series motor is operated on AC supply,

• An AC supply will produce a unidirectional torque because the direction of both the currents (i.e. armature current and field current) reverses at the same time
• Due to the presence of alternating current, eddy currents are induced in the yoke and field cores which results in excessive heating of the yoke and field cores
• Due to the high inductance of the field and the armature circuit, the power factor would become very low
• There is sparking at the brushes of the DC series motor
• It has poor efficiency

When the quantity of acids in the raining water is more than the average, then such rain is called 'Acid rain'.

We are aware that normally rainwater has a pH of 5.6. When the pH of the rainwater drops below 5.6, it is called acid rain.

Acid rain refers to the ways in which acid from the atmosphere is deposited on the earth’s surface. Oxides of nitrogen and sulphur which are acidic in nature can be blown by the wind along with solid particles in the atmosphere and finally settle down either on the ground as dry deposition or in water, fog and snow as wet deposition.

The bad effects of acid rain

• When acid rain falls and flows as groundwater to reach rivers, lakes etc, it affects plants and animal life in the aquatic ecosystem
• Acid rain is harmful to agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth
• It causes respiratory ailments in human beings and animal
• It may also cause corrosion in many buildings bridges, monuments, fencing etc
• It causes irritation in the eyes and skin of human beings
• This rain reduces the lustre of the metals too
• Acid rain damages buildings and other structures made of stone or metal
• The Taj Mahal in India has been affected by acid rain

• Electron Shell (also called a Principle energy level) is the region where electrons revolve around the nucleus of an atom.
• The general formula of filling electron in the shell is 2(n²); where n is the number of the shell.

In an open device, the current through it is zero and the voltage is unknown
Important:
Short Circuit: It is an electrical circuit that allows a current to travel along an unintended path with zero or very low electrical impedance. This results in an excessive amount of current flowing into the circuit.
Ideally, it has zero resistance, hence high current will flow and no voltage drop across the terminals.
Open Circuit: It is a circuit where no current flows. Any circuit which does not have a return path to flow current is an open circuit.
It has infinite resistance, hence no current will flow.
Short circuit and open circuit can be represented as shown in the figure.

The time constant of series RC circuit is, τ = RC = 300 × 0.01 × 10^-3 = 0.003 sec

The force exerted is given by: