Q.The signal is affected by noise in a communication system
Concept understanding — Elements of a Communication System
A communication system, regardless of what it carries, is built from three essential blocks connected in a chain: a transmitter, a channel, and a receiver, with noise capable of entering and corrupting the signal at any point along the channel. The transmitter converts the message signal - first turned into electrical form by a transducer if it wasn't already electrical, as with sound - into a form suited to the channel. The channel, wired or wireless, carries the transmitted signal to the receiver, but may distort it or add noise along the way. The receiver then processes the received (possibly corrupted) signal to reconstruct a usable version of the original message for the end user. Communication happens either point-to-point (one transmitter, one receiver, e.g. a telephone call) or as a broadcast (one transmitter serving many receivers at once, e.g. radio or television).
Noise is picked up mainly while the signal travels through the communication channel, not at the transmitter or modulator.
(c) In the channel
Step 1. Noise is any undesirable electrical signal that interferes with and attenuates the transmitted signal; it may be man-made (vehicles, welding machines, motors) or natural (lightning, solar/stellar radiation).
Step 2. The transmitter and modulator are where the signal is generated and shaped -- these stages are internal, shielded circuitry and are not exposed to the external disturbances that constitute noise.
Step 3. The communication channel is the medium (wireline or wireless/free space) carrying the signal between transmitter and receiver, and it is while travelling through this open medium that the signal picks up external man-made and natural noise.
Step 4. Eliminating the others: (a) and (b) occur before the signal has left the transmitter and are not where external noise enters; (d) the receiver processes a signal that has already picked up noise in the channel -- it does not itself introduce the noise.
(c) In the channel
Recall noise's definition -- an undesirable signal picked up while the transmitted signal travels through the communication channel/medium.
- Thinking the receiver 'causes' the noise, rather than merely receiving a signal that already picked up noise in the channel.
- Confusing internal circuit stages (transmitter, modulator) with the external transmission medium where interference actually enters.
Showing the 12 most recent of 14 on this concept.
- CBSE 2026Set A1 markMCQQ.'World Wide Web' was invented by (A) Tim Berner-Lee (B) John Logie Baird (C) Alexander Bain (D) G. Marconi
›Reveal solutionSolution
The World Wide Web was invented by Tim Berners-Lee (1989).
The World Wide Web — the system of interlinked hypertext documents accessed over the Internet — was invented by the British scientist Tim Berners-Lee in 1989 while at CERN. John Logie Baird is associated with television, Alexander Bain with the fax machine, and G. Marconi with radio (wireless telegraphy).
✓Final answer(A) Tim Berners-Lee.
- CBSE 2026Set A1 markMCQQ.The example of a broadcast mode of communication is (A) radio (B) telephone (C) television (D) both (A) and (C)
›Reveal solutionSolution
Broadcast communication sends the same signal from one transmitter to many receivers — radio and television both do this.
Communication modes are classified as point-to-point (a dedicated link between two specific users, e.g. a telephone) or broadcast (one transmitter serves a large number of receivers simultaneously). Radio and television both transmit a single signal that anyone with a receiver in range can pick up, so both are broadcast modes. A telephone connects two particular users, so it is point-to-point, not broadcast.
✓Final answer(D) both (A) and (C).
- CBSE 2026Set A1 markMCQQ.In a communication system, a repeater is (A) a receiver (B) a transmitter (C) a combination of a receiver and transmitter (D) none of these
›Reveal solutionSolution
A repeater is a receiver plus a transmitter: it picks up a weakened signal, amplifies and reconditions it, then retransmits it to extend range.
Signals attenuate over long distances. A repeater is placed along the path to overcome this: its receiver section picks up the incoming weak signal, the signal is amplified (and often reshaped), and its transmitter section sends it onward — usually at a different frequency to avoid interference. Thus a repeater is a combination of a receiver and a transmitter, used to extend the range of a communication system (as in satellite and mobile networks).
✓Final answer(C) a combination of a receiver and transmitter.
- CBSE 2025Set D1 markMCQQ.What type of wave is used in fibre optic communication? (A) Sound waves (B) Electromagnetic waves (C) Seismic waves (D) Mechanical waves
›Reveal solutionSolution
Fibre-optic communication carries signals as light pulses — electromagnetic waves — guided along the fibre by total internal reflection.
In optical-fibre communication, information is converted into pulses of light (usually infrared/visible) and sent down a thin glass or plastic fibre. Light is part of the electromagnetic spectrum, so the wave used is an electromagnetic wave.
The light stays inside the fibre by repeated total internal reflection at the core–cladding boundary. Sound, seismic and mechanical waves are not used — the carrier is electromagnetic.
✓Final answer(B) Electromagnetic waves.
- CBSE 2024Set A1 markMCQQ.The device which works of both modulation and demodulation is called (A) Laser (B) Radar (C) Modem (D) Fax
›Reveal solutionSolution
The device that performs both modulation and demodulation is the modem → option (C).
The word MODEM is short for MOdulator–DEModulator. At the transmitting end it modulates a carrier with the digital data (modulation), and at the receiving end it recovers the data from the received modulated signal (demodulation). This lets digital devices communicate over analog channels such as telephone lines.
✓Final answer(C) Modem.
- CBSE 2023Set ANNUAL1 markQ.What is the function of a repeater used in communication system? OR How does the effective power radiated from a linear antenna depend on the wavelength of the signal to be transmitted?
›Reveal solutionSolution
A repeater is a receiver-cum-transmitter unit that boosts a weakened signal and relays it further, increasing the effective communication range.
A repeater is a combination of a receiver and a transmitter placed between the original transmitter and the final receiver. Its function is:
- It receives the signal from the transmitter (or from a previous repeater), which has become weak/attenuated due to propagation over distance.
- It amplifies this weak signal (and, in digital systems, regenerates/re-times it to remove accumulated noise and distortion).
- It re-transmits the amplified signal onward, either to the next repeater or to the final receiver.
By repeating this process along a communication link, a repeater effectively increases the distance over which a signal can be reliably transmitted, extending the overall range of the communication system (this is exactly how signals are relayed over very long distances, e.g. via a chain of microwave repeater towers or satellite transponders acting as repeaters).
✓Final answerA repeater receives an attenuated signal, amplifies (and regenerates) it, and retransmits it — this increases the effective range of a communication system.
- CBSE 2023Set ANNUAL1 markMCQQ.In communication system, noise is most likely to affect the signal(a) at the transmitter(b) in the transmission medium(c) in the information source(d) at the destination
›Reveal solutionSolution
Noise is unwanted signal picked up along the path (channel) the signal travels through, so it is the transmission medium where it corrupts the signal most.
Noise refers to unwanted signals that tend to disturb the transmission and processing of a message signal. It typically enters the system from the environment surrounding the transmission channel — atmospheric disturbances, interference from other signals, thermal noise in the medium, etc. — while it travels from the transmitter to the receiver. The transmitter and receiver are engineered/shielded systems, and the information source is the original message itself (not yet exposed to the channel), so the channel (transmission medium) is where corruption is most likely to be picked up.
✓Final answerNoise is most likely to affect the signal in the transmission medium (option b).
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following is not a transducer ?(a) Loudspeaker(b) Amplifier(c) Microphone(d) All of these
›Reveal solutionSolution
A transducer converts one FORM of energy into another; an amplifier only strengthens an electrical signal, staying within the same form of energy.
Why: A loudspeaker converts electrical energy into sound (mechanical) energy — a transducer. A microphone converts sound energy into electrical energy — also a transducer. An amplifier takes a weak electrical signal and produces a stronger electrical signal at its output; the energy remains electrical throughout, so no energy-form conversion occurs, and it does not qualify as a transducer.
✓Final answerAmplifier is not a transducer — option (b).
- CBSE 2020Set ANNUAL1 markQ.Draw block diagram of a communication system.
›Reveal solutionSolution
Figure — Left-to-right block diagram of a generalized communication system A communication system is represented as a chain of blocks: the message is picked up, converted to a signal, transmitted through a channel (which adds noise), then received and converted back for the user.
The basic block diagram of a communication system consists of the following blocks connected in sequence:
- Information Source — originates the message (e.g. a person speaking).
- Input Transducer — converts the message (sound, image, etc.) into an electrical signal.
- Transmitter — processes the electrical signal (amplification, modulation) so it can be transmitted efficiently over the channel; includes the Modulator.
- Channel — the physical medium (wire, free space, optical fibre) through which the signal travels from transmitter to receiver. Noise is shown as an external input added to the signal in the channel.
- Receiver — extracts the original message signal from the received (possibly noisy, attenuated) signal; includes the Demodulator.
- Output Transducer — converts the electrical signal back into its original form (sound, image).
- Destination — the person/device for whom the message is intended.
Schematically: Information Source → Input Transducer → Transmitter → Channel (+ Noise) → Receiver → Output Transducer → Destination
✓Final answerInformation Source → Input Transducer → Transmitter (Modulator) → Channel (Noise added here) → Receiver (Demodulator) → Output Transducer → Destination.
- CBSE 2019Set HE2341 markQ.Give answer in one sentence: What is transducer?
›Reveal solutionSolution
A transducer converts one form of energy into another — e.g. sound into electrical signals (microphone) or electrical signals back into sound (loudspeaker).
A transducer is any device that converts one form of energy into another form. In the context of communication systems, an important example is a device that converts a sound (audio) signal into a corresponding electrical (voltage/current) signal, such as a microphone; the reverse conversion — electrical signal into sound — is performed by a loudspeaker. Transducers are essential at the input of a communication system (to generate an electrical message signal from the original information) and at the output (to convert the received electrical signal back into a form the user can perceive).
Note (Madhya Pradesh syllabus): This concept belongs to the Communication Systems chapter of the pre-2023 NCERT syllabus, which is not part of MP's current rationalised syllabus; the answer is given here for completeness.
✓Final answerA transducer is a device that converts one form of energy into another (e.g. sound energy into electrical energy, as in a microphone).
- CBSE 2018Set ANNUAL1 markMCQQ.Which of the following devices converts message signals into equivalent electrical signals?(a) Converter(b) Transformer(c) Transducer(d) Inverter
›Reveal solutionSolution
A transducer is any device that converts a physical quantity or message (sound, pressure, light, etc.) into a proportional electrical signal, making it the device that turns a 'message' into an electrical form for transmission.
In a communication system, the message to be conveyed (such as a voice or an image) usually starts out as a non-electrical signal. Before it can be transmitted electronically, it must be converted into an equivalent electrical (voltage/current) signal. The device that performs this energy conversion is called a TRANSDUCER — for example, a microphone (sound to electrical signal) or a photodiode (light to electrical signal).
The other options do different jobs: a converter changes one form of electrical signal/quantity to another (e.g., AC to DC), a transformer changes AC voltage/current levels via mutual induction, and an inverter changes DC to AC — none of these convert a non-electrical message signal into an electrical one.
✓Final answer(c) Transducer.
(Note: this question is from the Communication Systems chapter, which was removed entirely from the CBSE Physics syllabus in the 2023 rationalisation. It is outside today's Jharkhand-taught chapter set, though it was legitimately in syllabus for this 2018 paper.)
- CBSE 2018Set ANNUAL1 markMCQQ.Meaning of "FAX" is -(a) Full Access Transmission(b) Facsimile Telegraphy(c) Factual Auto Access(d) Feed Auto Exchange
›Reveal solutionSolution
FAX = Facsimile Telegraphy — transmitting an exact reproduction of text/images over a channel.
FAX is short for 'facsimile', meaning an exact copy. In facsimile telegraphy, a document is scanned, converted to an electrical signal, transmitted over telephone or radio links, and reconstructed as an identical printed copy at the receiver.
✓Final answer(b) Facsimile Telegraphy.
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