BEL Trainee Engineer Electronics Mock Test - 7 - Electronics and Communication Engineering (ECE) MCQ

Concept:

In a p-n junction diode, diffusion capacitance is given by

Where, rd = dynamic resistance

Where,

g_d = dynamic conductance

τ is the mean lifetime of minority carriers

Analysis:

Given:

C_D = 2 × 10^-7 F, τ = 5 μs

∴  2 × 10^-7 = 5 × 10^-6 × g_d

The frequency deviation in a phase-modulated carrier is proportional to the amplitude and frequency of the modulating signal both.

Derivation:

A general expression for a phase-modulated wave is:

xPM (t) = A cos [2πfct + kpm(t)]

The instantaneous angle is given as:

ϕi(t) = 2πfct + kp m(t)

The instantaneous frequency (in Hz) will be obtained as:

Frequency deviation is given by:

For a single tone modulation:

m(t) = Am sin ωmt

The frequency deviation becomes:

Δf ∝ Am fm

Fan-Out: It is an important characteristic of digital logic families to analyze the operation of the logic

gates.

CMOS has the maximum fan-out capacity.

Additional Information

Fan-Out is the maximum number of inputs that can be connected to the output of a gate without affecting the normal operation.

Fan-out can be calculated under two condition:

1)

When the output of the logic gate is high or at logic ‘1’ i.e. called current sourcing

Fan out  

Where,

I_OH = Current flow when the logic gate at a high state

I_IH = current flow in the connected logic gates.

2)

When the output of the logic gate is low or at logic ‘0’ i.e. called current sinking.

Fan-out 

Where,

I_OL = current flow when the logic gate at a low state.

I_IL = current flow from the connected logic gates.

So finally we say that fan-out of any logic gate is the number of gates that can be driven by it.

Important Points

A comparison of the given logic families is as shown: 

Concept:

We know that:

• AND gate output is '0' (If any input is '0').
• AND gate output is '1' (If all inputs are '1').
• OR gate output is '1' (If any input is '1').
• OR gate output is '0' (If all inputs are '0').

Analysis:

In the given logic circuit:

Inputs: A, B, C, D

Output: x, y, z

Let us assume , name of AND gates are A₁,  A₂,  A₃

Solution:

Output of A₁ = 

Output of A₂ =

Output of A3 =

Output x =Output of A₁ +Output of A₂ 

Output y =Output of A2 +Output of A3 

Output z =Output of A3

 = A.B.C.D

Feedback System:

• A Feedback System is one in which the output signal is sampled and then fed back to the input to form an error signal that drives the system, and depending on the type of feedback used, the feedback signal which is mixed with the systems input signal, can be either a voltage or a current.
• Feedback will always change the performance of a system and feedback arrangements can be either positive (regenerative) or negative (degenerative) type feedback systems.
• If the feedback loop around the system produces a loop-gain that is negative, the feedback is said to be negative or degenerative with the main effect of the negative feedback is in reducing the system’s gain.
• If however, the gain around the loop is positive, the system is said to have positive feedback or regenerative feedback. The effect of positive feedback is to increase the gain which can cause a system to become unstable and oscillate especially if GH = -1.
• A closed-loop control system is also known as feedback control system.

Concept:

The general expression for a frequency modulated wave is given by:

SPM(t) = A_c [cosω_ct + k_pm(t)]

The instantaneous phase is given by:

Phase deviation is defined as:

Phase deviation = [Max [k_p m(t)]]

Instantaneous frequency is given by:

From the above, the frequency deviation will be:

Frequency deviation maximum

Calculation:

k_p = 2 rad/volts

To avoid inter symbol interference, the minimum bandwidth 

R_s is signalling rate

In 64-QAM 6-bits are sent together as a symbol

= 100 kHz

Concept:

The equivalent inductance for a coil is given by:

Case 1: For additive polarity

When the current either enters or leaves from both the windings of the coil, then the coil is said to be connected in additive polarity.

Case 2: For subtractive polarity

When the current enters from one winding and leaves from another winding of the coil, then the coil is said to be connected in subtractive polarity.

Explanation:

In the given circuit, the current is leaving from both the windings of the coil.

Hence, the coil is connected in additive polarity.

• In fiber-optic communication, a diode laser is used for transmitting light signals into the fiber, and a photodiode is used for receiving the light signal.
• A photodiode is a device that converts a light signal to an electrical signal
• A photodiode is operated in the reverse-biased mode

Some important photodiodes are:

• PN photodiode
• PIN photodiode
• Avalanche photodiode

Notes:

PIN DIODE has three regions:

• P-type layer
• Intrinsic Layer
• N-Type layer
• The depletion region that exists between p and n regions is large. The layer between p and n regions includes no charge carriers
• In the reverse bias, as the depletion region of the diode has no charge carriers it works as an insulator
• The depletion region exists within the PIN diode but if the PIN diode is forward biased then carriers come into the depletion region and there will be a flow of current.

Concept: 

We know,

where,

R = Resistance

ρ = Resistivity of conductor

L = Length of conductor

A = Cross-sectional area of the conductor.

So, Resistance ∝ Resistivity

Calculation:

Given, Resistance of gold = 0.8 Ω 

And Resistivity of measuring wire = 25 × gold resistivity

∴ Resistance of wire = 25 × gold resistance

= 25 × 0.8 Ω 

= 20 Ω 

In TCP/IP, presentation layer, session layer and application layer are merged into one application layer/ process layer. So, option 1 is correct.

Both the models are logical models and having similar architecture as both the models are constructed with the layers. So, option 2 is also correct

→ OSI is based on vertical approach

→ TCP/IP is based on horizontal approach

So, option 3 is incorrect

Fibers that carry more than one mode are called multimode fibers. There are two types of multimode fibers:

1) Step Index

2) Graded Index

A comparison for step and graded fibers are respectively shown below:

We observe that in graded-index multimode optical fiber, the refractive index of the core is maximum at the fiber axis and decreases gradually towards the cladding.

Important Notes:

The multimode step-index multimode fiber suffers from Modal dispersion.

• Rays of light enter the fiber with different angles to the fiber axis. The limit is the fiber’s acceptance angle.
• Rays that enter with a shallow angle travel a more direct path and arrive sooner than those that enter at steeper angles.
• This arrival of different modes of light at different times is called modal dispersion.

The correct answer is option 2): Series in the control circuit

Concept:

• The push button switch is usually used to turn on and off the control circuit.
• It is used in electrical automatic control circuits to manually send control signals to control contactors, relays, electromagnetic starters, etc. 
• It is connected in series with the motor control circuit

Additional Information

• The threaded neck inserts through a hole cut into a metal or plastic panel, with a matching nut to hold it in place.
• Thus, the button faces the human operator(s) while the switch contacts reside on the other side of the panel.
• When pressed, the downward motion of the actuator breaks the electrical bridge between the two NC contacts, forming a new bridge between the NO contacts.
• The common industrial push button shown below

​

Gas metal arc welding (GMAW) or Metal inert gas arc welding (MIG):

• In this process the arc is formed between a continuous, automatically fed, metallic consumable electrode and welding job in an atmosphere of inert gas, and hence this is called metal inert gas arc welding (MIG) process.

• The type of operation is generally used in GMAW is Semi automatic.

• MIG welding power sources control voltage; this is done by either voltage stepped switches, wind handles, or electronically.

• The amperage that the power source produces is controlled by the cross sectional area of the wire electrode and the wire speed, i.e. the higher the wire speed for each wire size, the higher the amperage the power source will produce.

• Argon is used in MIG welding as shielding gas.
• Argon is denser than air and settles over the joint to protect the molten pool from atmospheric gas contamination.
• In addition, argon is easy to ionize, so it handles a long arc at low voltages well.
• When the inert gas is replaced by carbon dioxide then it is called CO2 arc welding or metal active gas (MAG) arc welding.
• The common name for this process is gas metal arc welding (GMAW). 

An ammeter is an electrical device that is used to measure the current.

In an ammeter, a low-value resistance is connected in series with it.

This is done to ensure a low voltage drop on the ammeter.

Values of input resistance

The correct answer is CPU cycle.

• The time required for the fetching and execution of one simple machine instruction is CPU cycle time.
• The fundamental sequence of steps that a CPU performs is called CPU Cycle, it is also known as the "fetch-execute cycle,".
• In simpler CPUs, the instruction cycle is executed sequentially, each instruction being processed before the next one is started.
• In most modern CPUs, the instruction cycles are instead executed concurrently, and often in parallel, through an instruction pipeline
• A clock cycle, or simply a "cycle," is a single electronic pulse of a CPU.
• During each cycle, a CPU can perform a basic operation such as fetching an instruction, accessing memory, or writing data.

Additional Information

• ​Real-time is a level of computer responsiveness that a user senses as sufficiently immediate or that enables the computer to keep up with some external process.
• Seek time is the time which is required by the drive to pick the read/write head and take it to the proper track of the disk.
  • The seek time is a part of the access time where the latter also includes latency time and overhead time.
• Delay time is the time required for a digital signal to travel from the input(s) of a logic gate to the output.

• A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect error in data send by sender
• Vertical redundancy check (VRC) is an error-checking method used on an eight-bit ASCII character
• In VRC, a parity bit is attached to each byte of data, which is then tested to determine whether the transmission is correct
• In telecommunication, a Longitudinal redundancy check (LRC) is a form of redundancy check that is applied independently to each of a parallel group of bit streams

He told us that he had read Milton in a prose translation which he had borrowed from his teacher and enjoyed it.

When used as verbs, admonish means to warn or notify of a fault, whereas reprimand means to reprove in a formal or official way. Reprimand is also noun with the meaning: a severe, formal or official reproof.

Tenacious means determined and comes from tenacity. The word is not related to tenuous. Vacillating (Indecisive) is an antonym.

The author highlights the problem that recycling is not an easy process and there are many obstacles in the way of recycling

The requirements of recycling are manpower and tools. Man power and tools will be used in recycling.

The correct answer is ALU.

• The part of the CPU that performs logical operations is called ALU.

​Important Points

• There are 2 parts of the CPU:
  • Arithmetic and logic unit (ALU)
  • Control Unit

Key Points

• The arithmetic and logic unit (ALU)
  • The arithmetic and logic unit (ALU) is where the CPU performs the arithmetic and logic operations.
  • Examples of arithmetic operations are addition, subtraction, multiplication, and division.
  • Examples of logic operations are comparisons of values such as NOT, AND, and OR.
  • The Control Unit carries out instructions.

Additional Information

• The central processing unit (CPU)
  • The computer's central processing unit (CPU) is the device of a computer that retrieves and executes instructions. 
  • The major types of CPU are classified such as:
    • Single-core processor
    • Dual-core processor
    • Quad-core processor
    • Hexa core processor

As 'Ophthalmia' is a disease of 'Eye' in the same way 'Rickets' is the disease of 'Bone'.

1st term = 1
2nd term = 1 + (1) = 2
3rd term = 2 + (1) = 3
4th term = 3 + (3) = 6
5th term = 6 + (3) = 9
6th term = 9 + (9) = 18
7th term = 18 + (9) = 27
8th term = 27 + (27) = 54

Thus, the missing term is 7th term = 27

Transparent paper is folded from dotted line from upper to lower, then paper will be folded from right to left.

All are the parts of tree.