The correct answer is C. Intensity of sound.
A decibel (dB) is a logarithmic unit that expresses the ratio of two values of a physical quantity, often power or intensity. One decibel is one tenth of a bel, which is named after Alexander Graham Bell.
The decibel is a convenient unit for expressing very large or very small quantities. For example, the intensity of a whisper is about 30 decibels, while the intensity of a jet engine is about 120 decibels.
The decibel is also used to express the ratio of two sound pressures. The sound pressure level (SPL) is defined as 20 log10(p/p0), where p is the sound pressure and p0 is a reference sound pressure of 20 micropascals.
The decibel is a dimensionless unit, but it is often expressed with a prefix to indicate the quantity being measured. For example, dBm is used to express power
in milliwatts, and dBSPL is used to express sound pressure level.The decibel is a widely used unit in many fields, including physics, engineering, and acoustics. It is a convenient and unambiguous way to express the ratio of two quantities, and it is used to measure a wide variety of physical quantities.
The other options are incorrect because:
- Option A is incorrect because the speed of light is measured in meters per second.
- Option B is incorrect because the intensity of heat is measured in watts per square meter.
- Option D is incorrect because the frequency of radio waves is measured in hertz.