Communication Devices MCQ Quiz - Objective Question with Answer for Communication Devices - Download Free PDF

Explanation:

The unit used to measure sound intensity is: Decibel (dB).

Sound intensity is a measure of the power carried by sound waves per unit area in a direction perpendicular to that area. The unit used to quantify sound intensity is the decibel (dB). The decibel is a logarithmic unit used to describe a ratio, and it is commonly used in acoustics to express the intensity of sound.

Correct Option Analysis:

The correct answer is option 2: Decibel (dB).

Decibel (dB) is the standard unit of measurement for sound intensity. The decibel scale is logarithmic, which means that a small increase in the decibel level represents a large increase in the sound intensity. For example, an increase of 10 dB represents a tenfold increase in sound intensity.

The decibel scale is used because the human ear is capable of detecting a very wide range of sound intensities. The threshold of hearing (the quietest sound that can be heard) is typically defined as 0 dB, while sounds above 120 dB can cause immediate harm to the human ear.

Important Information:

To further understand the analysis, let’s evaluate the other options:

Option 1: Watt

The watt (W) is a unit of power in the International System of Units (SI). It is used to measure the rate of energy transfer or the rate of doing work. While the watt can be used to describe the power of an acoustic source (such as a loudspeaker), it is not the standard unit for measuring sound intensity.

Option 3: Newton

The newton (N) is a unit of force in the International System of Units (SI). It is used to measure the force exerted on an object. The newton is not used to measure sound intensity, as sound intensity is related to the energy carried by sound waves rather than the force exerted by those waves.

Option 4: Lux

The lux (lx) is a unit of illuminance in the International System of Units (SI). It is used to measure the amount of light that falls on a given surface area. The lux is not related to sound intensity and is used exclusively for measuring light intensity.

Conclusion:

Understanding the appropriate units of measurement for various physical quantities is essential for accurate communication and analysis in science and engineering. The decibel (dB) is the correct unit for measuring sound intensity, as it accounts for the logarithmic nature of human hearing and provides a practical way to describe the wide range of sound intensities that can be perceived by the human ear.

Explanation:

Microphone Functionality

Definition: A microphone is a device that captures sound waves and converts them into electrical signals. This conversion is essential for various applications, such as recording audio, amplifying sound, and enabling communication over long distances through electronic devices.

Working Principle: Microphones function by utilizing different types of transducers, which are components that convert one form of energy into another. In the case of a microphone, it converts acoustic energy (sound waves) into electrical energy (electrical signals). When sound waves reach the microphone, they cause the diaphragm (a thin membrane) to vibrate. These vibrations are then converted into electrical signals by various mechanisms, depending on the type of microphone.

There are several types of microphones, including dynamic microphones, condenser microphones, ribbon microphones, and more, each with its unique mechanism for converting sound to electrical signals:

• Dynamic Microphones: These microphones use electromagnetic induction to convert sound into electrical signals. The diaphragm is attached to a coil of wire situated within a magnetic field. When sound waves hit the diaphragm, it moves the coil within the magnetic field, generating an electrical current.
• Condenser Microphones: These microphones operate on the principle of capacitance change. The diaphragm is placed very close to a backplate, forming a capacitor. As the diaphragm vibrates due to sound waves, the distance between the diaphragm and the backplate changes, causing variations in capacitance, which are converted into electrical signals.
• Ribbon Microphones: These microphones use a thin metal ribbon suspended within a magnetic field. When sound waves strike the ribbon, it vibrates within the magnetic field, inducing an electrical current in the ribbon.

Applications: Microphones are used in various fields such as:

• Audio recording and broadcasting: Capturing sound for music production, podcasts, radio, and television.
• Communication devices: Facilitating voice communication in telephones, hearing aids, and intercom systems.
• Public address systems: Amplifying sound in live events, conferences, and public speeches.
• Speech recognition: Enabling voice commands and dictation in computing devices.

Correct Option Analysis:

The correct option is:

Option 3: Convert sound to electrical signals.

This option accurately describes the primary function of a microphone. The microphone's core purpose is to take acoustic energy (sound waves) and convert it into electrical energy (electrical signals). This conversion is fundamental to its operation, allowing sound to be recorded, amplified, and transmitted through electronic devices.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Amplify signals.

This option is incorrect because amplifying signals is not the primary function of a microphone. While microphones can be part of a system that includes amplification (such as in public address systems), their main role is to convert sound into electrical signals. The amplification process typically occurs after the sound has been converted into an electrical signal.

Option 2: Convert electrical signals to sound.

This option describes the function of a loudspeaker or a headphone, not a microphone. Loudspeakers take electrical signals and convert them back into sound waves, enabling us to hear the audio. Microphones perform the opposite function by capturing sound and converting it into electrical signals.

Option 4: Play background music.

This option is unrelated to the primary function of a microphone. Playing background music is the function of an audio playback device or a sound system, which might use microphones to capture sound but is not a function of the microphone itself.

Conclusion:

Understanding the primary function of a microphone is crucial for its effective application in various fields. A microphone's role is to convert sound waves into electrical signals, a process that is essential for audio recording, communication, and sound amplification. While other components in audio systems may amplify signals or convert electrical signals back into sound, the microphone's unique function is the initial conversion of sound to electrical signals.

Explanation:

Public Address System (PA System)

A Public Address (PA) system is an electronic amplification system used to reinforce sound, making it louder and distributing it to a wider audience. This system is commonly used in various settings such as schools, concerts, public gatherings, and events to convey information clearly and audibly. The basic components of a PA system include a microphone, amplifier, loudspeakers, and sometimes a mixer.

Correct Option Analysis:

The correct option is:

Option 3: Microphone

The microphone is the basic input device in a PA system. It converts sound waves (acoustic energy) into electrical signals. These electrical signals are then processed by the rest of the PA system to be amplified and broadcasted through loudspeakers. The role of the microphone is crucial as it captures the initial audio signal that will be amplified and transmitted to the audience.

Importance of the Microphone in a PA System:

The microphone's primary function is to capture sound accurately and convert it into an electrical signal. This conversion is essential as it allows for the amplification and distribution of sound over large areas. Without a microphone, the PA system would not have an initial audio signal to process and amplify. The quality of the microphone can significantly impact the overall sound quality of the PA system, making it a vital component.

Types of Microphones:

There are various types of microphones used in PA systems, each with its specific characteristics and applications:

• Dynamic Microphones: These are rugged and durable microphones that do not require a power source. They are commonly used for live performances and public speaking due to their ability to handle high sound pressure levels.
• Condenser Microphones: These microphones are more sensitive and provide a higher quality of sound. They require an external power source (usually phantom power) and are used in studio recordings and situations where capturing detail and clarity is essential.
• Wireless Microphones: These microphones transmit audio signals without the need for physical cables, offering greater mobility and flexibility. They are ideal for dynamic presentations and performances.

Working Principle:

When sound waves hit the diaphragm of the microphone, it vibrates in response. These vibrations are converted into electrical signals through electromagnetic induction (in dynamic microphones) or changes in capacitance (in condenser microphones). The electrical signal generated is then sent to the amplifier for further processing.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Loudspeaker

The loudspeaker is an output device in a PA system. It converts the amplified electrical signals back into sound waves, which are broadcasted to the audience. While essential, it is not the basic input device of the system.

Option 2: Amplifier

The amplifier's role in a PA system is to boost the low-level audio signals from the microphone to a higher power level. This amplified signal is then sent to the loudspeakers. The amplifier is a critical component but serves as a part of the signal processing rather than the initial input.

Option 4: Mixer

The mixer combines multiple audio signals and allows for adjusting their levels, tone, and effects before sending the mixed signal to the amplifier. While mixers are crucial for managing complex audio setups, they are not the basic input device.

Conclusion:

In a PA system, the microphone serves as the fundamental input device that captures sound and converts it into an electrical signal for amplification and distribution. Understanding the roles of each component in a PA system helps in optimizing its setup and ensuring clear and effective audio communication. The microphone's quality and type can significantly influence the system's performance, making it a critical element in achieving the desired sound reinforcement.

Explanation:

A public address system is primarily used for:

Correct Option Analysis:

The correct option is:

Option 3: Voice amplification and distribution

A public address system (PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound source or recorded sound or music. PA systems are used in any public venue that requires that an announcer, performer, etc. be sufficiently audible at a distance or over a large area. Typical applications include sports stadiums, public transportation vehicles and facilities, and live or recorded music venues and events.

Explanation:

A public address system is primarily designed to amplify and distribute sound, ensuring that voice or audio is heard clearly over a large area. This is crucial in scenarios where information needs to be conveyed to a large number of people simultaneously, such as in schools, hospitals, airports, and public gatherings. The system works by using a microphone to capture the sound, which is then amplified by an amplifier and broadcasted through loudspeakers. This allows the voice to reach a wider audience clearly and effectively.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Data transfer

This option is incorrect because data transfer involves the transmission of data from one point to another, which is typically done using data networks, such as the internet, intranets, or other data communication systems. A public address system is not designed for this purpose. Its primary function is to amplify and distribute sound, not data.

Option 2: Power distribution

This option is also incorrect. Power distribution involves the delivery of electrical power from power plants to homes, businesses, and other end-users. This is typically done through power lines and transformers in the electrical grid. A public address system does not have the capability to distribute electrical power; it uses electrical power to amplify and distribute sound.

Option 4: Video streaming

This option is incorrect as well. Video streaming involves the transmission of video content over the internet or other networks, allowing users to watch video content in real-time or on-demand. This is accomplished using video servers, content delivery networks, and streaming protocols. A public address system is not designed for streaming video; its primary function is to handle audio.

Conclusion:

A public address system is specifically designed for voice amplification and distribution. It is essential in environments where clear and effective communication to a large audience is necessary. The other options, such as data transfer, power distribution, and video streaming, are not relevant to the primary function of a public address system. Understanding the specific purpose of PA systems helps in identifying their appropriate applications and differentiating them from other technological systems.

The correct answer is option 1.

Liquid-crystal display (LCD)

• A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers.
• Liquid crystals do not emit light directly but instead, use a backlight or reflector to produce images in color or monochrome.
• LCD TV displays images by blocking white light.
• It operates by applying a varying electric voltage to a layer of liquid crystal, thereby inducing changes in its optical properties.

• The full-form of PSTN is “Public switched Telephone Network”.
• Public Switched Telephone Network is a Telecommunication network which is used for voice communication.
• PSTN is a circuit-switched network.
• In PSTN a unique Id called Telephone number is available for communication.

So option (4) is correct.

The range of frequencies over which the PLL can maintain lock with the incoming signal is called Lock Range or Tracking Range

In PLL (phase-locked loop), the capture range is always less than the lock range.

PLL is used to select the desired frequency channel in communication circuits.

The different states of PLL are:

Lock Range:

When PLL is in lock state it can track frequency changes in the incoming signal.

The range of frequencies over which the PLL can maintain lock with the incoming signal is called Lock Range or Tracking Range

Capture Range:

The Range of frequencies over which the PLL can acquire the lock with an input signal is called capture range.

Free Running state:

Initially, no input signal is applied. Under this condition, the phase detector and Low pass filter outputs will be zero. At this time, VCO operates at free-running frequency. This is the normal operating frequency of VCO.

• LTE stands for Long-Term Evolution. 
• LTE is a standard for wireless communication of high-speed data for mobile phones and data terminals.
• It is based on the GSM/EDGE and UMTS/HSPA network technologies.

Advantages of LTE are as follows:

• LTE brought much better spectral efficiency to cellular networks. 
• To support high data rates for services such as voice over IP (VOIP), video conferencing, or even a high-speed cellular modem, LTE is an ideal technology. 
• LTE supports flexible carrier bandwidths, from 1.4 MHz up to 20 MHz. Frequency Division Duplex (FDD) and Time Division Duplex (TDD), both schemes can be used on the same platform.​

VoLTE: 

• VoLTE is a technology update to the LTE protocol used by mobile phone networks.
• Under LTE, the infrastructure of telecom players only allows transmission of data while voice calls are routed to their older 2G or 3G networks.
• VoLTE always supports data and voice call services at the same time.
• Basically, VoLTE systems convert voice into the data stream, which is then transmitted using the data connection.

Nowadays, from phones to TVs, the screens used could be either a display based on OLED (Organic Light-Emitting Diode) technology or LCD (Liquid Crystal Display) technology.

Liquid Crystal Display:

• LCD stands for “Liquid Crystal Display”.
• It is a combination of two states of matter, the solid and the liquid. LCD uses a liquid crystal to produce a visible image.
• LCD’s technologies allow displays to be much thinner when compared to a cathode ray tube (CRT) technology.
• It is composed of several layers which include two polarized panel filters and electrodes.
• These screens work on the principle of blocking light rather than emitting light. LCDs require a backlight as they do not emit light by them.
• Most of electronic devices mainly depend on liquid crystal display technology for their display.

Hence, it can be concluded from the given points that the acronym LCD stands for Liquid Crystal Display.

Concept:

• A television receiver (TV receiver) is a device that combines a tuner, display, loudspeaker to view and hear television broadcasting through satellite or cable.
• In a TV receiver CRT (Cathode Ray Tube) is responsible for the deflection of the beam, and the beams are bent by magnetic deflection.
• A varying magnetic field is generated by the coil and driven by an electronic circuit around the neck of the tube responsible for beam deflection.

So in the TV receiver electron beam is deflected by Electromagnetic deflection.

Option 1 correct choice.

More information:

Electrostatic deflection refers to a technique for modifying the path of a beam of a charged particle by the use of an electric field. applied transverse to the path of the particle.

Lorentz force I,e. F = qE + qV × B is responsible for electrostatic deflection.

q = charge, V = velocity, E = electric field, B = Magnetic field.

Electrostatic deflection is mainly used for small screen therefore not suitable for the CRT used in TV receivers.

Mechanism of LCD:

• The LCD consists of a large number of pixels, or picture elements, consisting of liquid crystal molecules held between two sets of transparent electrodes.
• The liquid crystals react in predictable ways when the electrical charge running between those electrodes is changed — meaning they twist and move in ways that let different amounts (and colors) of light through the crystals. 
• When compared to the other type of flat-panel display (plasma), LCDs tend to be found on the smaller size of the spectrum.

• A television channel is a terrestrial frequency or virtual number over which a television station or television network is distributed. 
• TV stations make their broadcasts by sending specially-encoded radio signals over the air. 
• Individual television stations are usually granted licenses by a government agency to use a particular portion of the radio spectrum (a channel) through which they send their signals.
• Channels may be shared by many different television stations depending upon the location and service provider. 
• Analog television channels are typically 6, 7, or 8 MHz in bandwidth. 

Comparison between LED TV and LCD TV

The correct answer is option 1.

Liquid-crystal display (LCD)

• A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers.
• Liquid crystals do not emit light directly but instead, use a backlight or reflector to produce images in color or monochrome.
• LCD TV displays images by blocking white light.
• It operates by applying a varying electric voltage to a layer of liquid crystal, thereby inducing changes in its optical properties.

Duplexing: It is a phenomena in computer modes that allows simultaneous transmission and reception in both the directions. 

Simplexing: It is a phenomena in computer modes that allows telecommunication in only one direction.