RRB JE Electrical (CBT II) Mock Test- 5 - Electrical Engineering (EE) MCQ

Ripple factor may be defined as the ratio of the root mean square (rms) value of the ripple voltage to the absolute value of the DC component of the output voltage, usually expressed as a percentage. It is expressed as peak to peak value.

Now for the full wave rectifier,

RMS value= Vm/1.414

Avg. Value= 2*Vm/3.14

Ripple factor = rms/avg = 0.48

The total reluctance is equal to the ratio of the MMF in a passive magnetic circuit and the magnetic flux in this circuit. In an AC field, the reluctance is the ratio of the amplitude values for a sinusoidal MMF and magnetic flux.
R = F/Φ

On December 30, 1906, Muslim league was formed under the leadership of Aga Khan, the Nawab of Dhaka.

When a voltage greater than pinch off is applied, the current starts flowing from drain to source. Pinch off voltage is the drain to source voltage after which the drain to source current becomes almost constant and JFET enters into saturation region and is defined only when gate to source voltage is zero

In PMMC instruments, the deflecting torque is given by

Td = BINA

Where Td = Deflecting torque in N-m

B = Flux density, wb/m2

I = Current in the Coil, amperes

N = Number of turns of the coil

A = Effective coil area m2

Deflecting torque is directly proportional to current.

Maxwell’s inductance capacitance bridge is used for the measurement of an inductance of medium Q coils.

Hay’s bridge is used to measure for the measurement of an inductance of high Q coils.

Anderson Bridge is the most common and best bridge method for precise measurement of inductance over a wide range.

To determine the polarity of the voltage drop across the resistor, it is necessary to know the direction of the current through the resistor.

The terminal entering the current gives a positive sign of voltage drop.

For a fixed kVA rating, more the designed frequency of transformer then lesser will be cross sectional area of the core. Hence lesser will be the size and weight of transformer.

The colour of different pH indicators in different mediums is summarized in the table below:

In the armature-voltage control method of speed control of a DC shunt motor, as the speed is increased the torque remains constant and the power increases which is shown in above figure.

The gate voltage in a JFET at which drain current becomes zero is called pinch-off voltage

Pinch off voltage:

• It is the drain to source voltage after which the drain to source current becomes almost constant and JFET enters saturation region and is defined only when gate to source voltage is zero

Potentiometer is an instrument which is used to measure a known emf by comparison with known emf.

Sensitivity of potentiometer is the smallest potential difference can be measured using the potentiometer. It can be decreased by increasing its potential gradient. Thus, it can be decreased by following methods.

1) By decreasing length of the potentiometer wire as the length of the wire is directly proportional to resistance.

2) If the potentiometer wire is a fixed length, the potential gradient can be increased by increasing the current in the circuit by varying rheostat.

Harper Lee was the author of the book “To kill a Mockingbird” who died at an age of 89 in 2016.

• Anshula Kant, Managing Director of the State Bank Of India, has been appointed as Managing Director and Chief Financial Officer of the World Bank.
• She will be responsible for financial and risk management of the World Bank Group.
• Anshula brings more than 35 years of expertise in finance, banking, and innovative use of technology through her work as CFO of the State Bank of India.

Given J is the current density at a given location in a resistive material, E is the electric field at that location, and σ is a material-dependent parameter called the conductivity, Ohm’s law can be expressed as

J = σE

Where,

j → is the current density

E → is the electric field inside the conductor

And σ is the electrical a conductivity of the material

An armature control method is used in the DC shunt motor.
In a DC motor, the back emf is directly proportional to speed and flux.
E_b ∝ Nϕ
Where N is speed and ϕ is flux.|
In a DC shunt motor, flux is constant.
So, the back emf is directly proportional to speed.
Important Point:
Armature resistance control:
We know that,
N ∝ E_b/ø
N ∝ V- I _a(R_a + R)/ø
We can control the speed by increasing armature resistance. This method gives only below base speeds. This method is a constant torque and variable power drive.
Field control method:
We know that
N ∝ E_b/ø
N ∝ V- I _a(R_a + R)/ø
By varying flux, we can increase the speed more than its base speed. This method is constant power and variable torque drive.
The characteristics are shown below

Concept:
We know that
P = V²/R
Here P = Power, V = Voltage, R = Resistance
Calculation:
R = 230²/100 = 529 Ω

The four band colour code is the most common variation. These resistors have two bands for the resistance value, one multiplier and one tolerance band

We known that
Power = I²R

Now milliammeter resistance = 200
∴ Power consumed = I²R = 1 × 10^-3 × 200 = 0.2 mW

• The diode in which impurities are heavily doped is Tunnel diode
• Tunnel diode owing to heaving doping (typically 100 to several thousand times normal doping semiconductor diode) resulting in extremely small depletion layer width
• Due to this extremely thin depletion region width the charge carriers can “tunnel" through depletion region

Dummy coils:

• The wave winding is possible only with number of conductor or coils.
• But sometimes the armature slots available in the armature winding do not meet the requirement of the winding. (It means that the available number of slots is more than the required number of conductors).
• Some slots are kept without armature winding in that case and dummy coil or coils are employed in that slots.
• The dummy coils are similar to other coils except their ends are cut, short and taped. They do not connect with the commutator bars.
• The dummy coils are simply to provide mechanical balance for the armature.
• As they do not connect with commutator bars, they do not affect the electrical characteristics of the winding.

Concept:

• Esters are sweet-smelling substances.
• These are used in making perfumes and as flavouring agents.
• Esters react in the presence of an acid or a base to give the alcohol and salt.
• This reaction is known as saponification because it is used in the preparation of soap

Underlying reaction:
CH₃COOC₂H₅ + NaOH → C₂H₅OH + CH₃COONa

The advantages of the parallel operation of DC generators are -

Continuity of service: If a single large generator is used in the power plant, then in case of its breakdown, the whole plant will be shut down. If power is supplied from a number of small units operating in parallel, then in case of failure of one unit, the continuity of supply can be maintained by other healthy units.

Efficiency: Generators run most efficiently when loaded to their rated capacity. Electric power costs less per kWh when the generator is efficiently loaded. Therefore, when load demand on power plant decreases, one or more generators can be shut down and the remaining units can be efficiently loaded.