thermal noise: meaning, definition, pronunciation and examples
C2Technical/Scientific
Quick answer
What does “thermal noise” mean?
In electronics and communications, the inherent, random electrical fluctuations present in all conductors due to the thermal agitation of charge carriers (electrons).
Audio
Pronunciation
Definition
Meaning and Definition
In electronics and communications, the inherent, random electrical fluctuations present in all conductors due to the thermal agitation of charge carriers (electrons).
A fundamental type of electrical noise that is present even without an applied signal; its power is proportional to absolute temperature and bandwidth. The concept also appears in related fields like physics and imaging to describe random background signals.
Dialectal Variation
British vs American Usage
Differences
No significant lexical or spelling differences. British usage may prefer 'thermal noise' over 'Johnson–Nyquist noise' more consistently, while American engineering texts might use the terms interchangeably. The hyphenated term 'Johnson–Nyquist' may be styled differently (en dash vs. hyphen).
Connotations
Identical technical connotations in both varieties.
Frequency
Equally low-frequency in general language, but standard and equally frequent within electronics, physics, and engineering contexts in both the UK and US.
Grammar
How to Use “thermal noise” in a Sentence
The [noun phrase] is dominated by thermal noise.Thermal noise in the [component] limits the sensitivity.[Verb] the thermal noise to determine the [parameter].Vocabulary
Collocations
Examples
Examples of “thermal noise” in a Sentence
verb
British English
- The receiver's performance is thermal-noise-limited.
- The circuit was thermal-noise-dominated.
American English
- The system is thermal-noise-limited.
- They thermal-noise-characterized the amplifier.
adverb
British English
- [Not standard. Typically not used adverbially.]
American English
- [Not standard. Typically not used adverbially.]
adjective
British English
- The thermal-noise performance was exceptional.
- A thermal-noise analysis was conducted.
American English
- The thermal-noise figure was too high.
- We need a thermal-noise measurement.
Usage
Meaning in Context
Business
Virtually never used.
Academic
Used in physics, engineering, and electronics papers. Example: 'The detector's performance was limited by thermal noise.'
Everyday
Not used in everyday conversation. A layperson would simply say 'background static' or 'hiss'.
Technical
Core term in electrical engineering, communication theory, signal processing, and physics. Example: 'The amplifier's equivalent noise temperature was calculated from the thermal noise power.'
Vocabulary
Synonyms of “thermal noise”
Strong
Neutral
Weak
Vocabulary
Antonyms of “thermal noise”
Watch out
Common Mistakes When Using “thermal noise”
- Pronouncing 'thermal' as /ˈθɜːmæl/ instead of /ˈθɜːməl/.
- Using 'thermal noise' to refer to any electronic interference (e.g., from power lines).
- Confusing it with 'shot noise', which is particle-based, not temperature-based.
- Treating it as a countable noun (e.g., 'a thermal noise') – it's typically uncountable.
FAQ
Frequently Asked Questions
In many practical contexts, yes, because thermal noise has a flat (white) power spectral density over a wide frequency range. However, 'white noise' is a broader mathematical description of any signal with a flat spectrum, while 'thermal noise' specifies the physical origin.
No, it is a fundamental physical phenomenon. It can only be reduced by lowering the temperature of the component (e.g., using cryogenic cooling) or by reducing the bandwidth of the measurement.
It was first observed and measured by John B. Johnson at Bell Labs in 1926, and its theoretical explanation was provided by Harry Nyquist, also at Bell Labs, in 1928. Hence the synonyms 'Johnson' or 'Johnson–Nyquist' noise.
You are unlikely to notice it directly. It contributes to the faint background hiss you might hear when turning a stereo amplifier up very high with no input, or the 'snow' in a very weak analogue TV signal (historically). It is a key design factor in mobile phone receivers, GPS, and radio astronomy.
In electronics and communications, the inherent, random electrical fluctuations present in all conductors due to the thermal agitation of charge carriers (electrons).
Thermal noise is usually technical/scientific in register.
Thermal noise: in British English it is pronounced /ˈθɜːm(ə)l nɔɪz/, and in American English it is pronounced /ˈθɝːməl nɔɪz/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “[No idioms; the term is purely technical.]”
Learning
Memory Aids
Mnemonic
Think of 'thermal' as 'heat' and 'noise' as 'hiss'—it's the 'heat hiss' inherent in all electronic components.
Conceptual Metaphor
ELECTRICAL NOISE IS UNWANTED SOUND; A FUNDAMENTAL BARRIER IS A FLOOR (as in 'noise floor').
Practice
Quiz
What is the primary cause of thermal noise?