The loss of energy as a signal propagates outward is known as ______.
2021
The loss of energy as a signal propagates outward is known as ______.
Answer: C. Attenuation — Concept. A transmission medium is never perfect, so every signal that crosses it is degraded on the way. The classical transmission impairments are separated…
- A.
Noise
- B.
Distortion
- C.
Attenuation
- D.
Scattering
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Correct answer: C
Concept. A transmission medium is never perfect, so every signal that crosses it is degraded on the way. The classical transmission impairments are separated by what they change about the signal: its power (how strong it is), its shape (how its frequency components line up in time), or its content (what extra energy has been mixed into it).
Application. The stem describes energy being lost while the signal travels outward, so the property that changes is the signal's power. The impairment defined as a fall in signal power over distance is Attenuation: as the wave propagates, the resistance of the medium converts part of its energy into heat, so less power arrives than was launched.
Engineers measure this loss in decibels:
dB = 10 log10 (P2 / P1)
where P1 is the transmitted power and P2 the received power; a negative value means power was lost. Because the loss grows with distance, amplifiers (on analog links) and repeaters (on digital links) are spaced along a long line to restore the level.
Contrast. Each transmission impairment is named by the property of the signal it changes:
Impairment | What it changes about the signal |
|---|---|
Noise | Unwanted energy is added to the signal by thermal agitation, induced pickup, crosstalk or impulse sources, so the receiver sees content the sender never transmitted; the effect is judged by the signal-to-noise ratio. |
Distortion | The shape of a composite signal changes because its frequency components travel at different speeds and arrive with different delays; the form of the waveform, not its level, is what has altered. |
Scattering | Part of the signal is redirected into other directions by particles or refractive-index irregularities, as in Rayleigh scattering in optical fibre; this names one physical mechanism of redirection, not the general loss of level along a link. |
Attenuation | The power of the signal falls as it travels, because the resistance of the medium converts part of the signal energy into heat. |
Cross-check. Ask which property of the signal changed:
Content added to the signal — Noise
Shape of the waveform changed — Distortion
Part of the signal redirected — Scattering
Power of the signal lost — Attenuation
The stem states that energy is lost as the signal propagates outward, so power is the property that changed, which fixes the answer at Attenuation.