Rayl

Key takeaways

Rayl belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Rayl to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Rayl from memory before moving on to harder problems.

Reference excerpt

A rayl (symbol Rayl) is one of two units of specific acoustic impedance and characteristic acoustic impedance; one an MKS unit, and the other a CGS unit. These have the same dimensions as momentum per volume. The units are named after John William Strutt, 3rd Baron Rayleigh. They are not to be confused with the unit of photon flux, the rayleigh.

Explanation

Specific acoustic impedance When sound waves pass through any physical substance the pressure of the waves causes the particles of the substance to move. The sound specific impedance is the ratio between the sound pressure and the particle velocity it produces. Specific acoustic impedance is defined as:

Z _ ( r , ω ) = p _ ( r , ω ) v _ ( r , ω ) {\displaystyle {{\underline {Z}}(\mathbf {r} ,\omega )={\frac {{\underline {p}}(\mathbf {r} ,\omega )}{{\underline {v}}(\mathbf {r} ,\omega )}}}}

where Z _ , p _ {\displaystyle {\underline {Z}},{\underline {p}}} and v _ {\displaystyle {\underline {v}}} are the specific acoustic impedance, pressure and particle velocity phasors, r {\displaystyle \mathbf {r} } is the position and ω {\displaystyle \omega } is the frequency.

Characteristic acoustic impedance The rayl is also used for the characteristic (acoustic) impedance of a medium, which is an inherent property of a medium:

Z 0 = ρ 0 c 0 {\displaystyle {Z_{0}=\rho _{0}c_{0}}}

Here, Z 0 {\displaystyle {Z_{0}}} is the characteristic impedance, and ρ 0 {\displaystyle {\rho _{0}}} and c 0 {\displaystyle {c_{0}}} are the density and speed of sound in the unperturbed medium (i.e. when there are no sound waves travelling in it). In a viscous medium, there will be a phase difference between the pressure and velocity, so the specific acoustic impedance Z _ {\displaystyle {\underline {Z}}} will be different from the characteristic acoustic impedance Z 0 {\displaystyle {Z_{0}}} .

MKS and CGS units Subscripts are used in this section to distinguish identically named units. Texts often refer to "the MKS rayl" to ensure clarity. The MKS unit of specific acoustic impedance is the pascal-second per meter, and is often called the rayl (MKS: 1 Rayl = 1 Pa·s·m−1). The MKS unit and the CGS unit confusingly have the same name, but are not the same quantity (or unit):

As an MKS unit, one rayl equals one pascal-second per meter (Pa·s·m−1), or equivalently one newton-second per cubic meter (N·s·m−3). Expressed in SI base units, that is kg·s−1·m−2: 1 RaylMKS = 1 N⋅s/m3 = 1 Pa⋅s/m = 1 kg/(s⋅m2) As a CGS unit, one rayl equals one barye-second per centimeter (ba·s·cm−1), or equivalently one dyne-second per cubic centimeter (dyn·s·cm−3). Expressed in CGS base units, that is g·s−1·cm−2: 1 RaylCGS = 1 dyn⋅s/cm3 = 1 ba⋅s/cm = 1 g/(s⋅cm2) The CGS unit rayl is ten times larger than the MKS unit rayl: 1 RaylCGS = 10 RaylMKS

References Citations

Sources

External links Dictionary of Physics Units of Measurement A discussion of the history and ambiguity of the rayl

Worked examples

Example 1 — a first encounter with Rayl

Start with the simplest possible case. Write down what Rayl claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Rayl before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Rayl ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Rayl

In research: Rayl appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Rayl in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Rayl is common in secondary-school and first-year university syllabi. It links to neighbouring topics Non-SI metric units, Units of measurement, so understanding it makes those chapters shorter.
In everyday life: Look for Rayl outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Rayl in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Rayl means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Rayl out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Rayl in simple terms?

A rayl (symbol Rayl) is one of two units of specific acoustic impedance and characteristic acoustic impedance; one an MKS unit, and the other a CGS unit. These have the same dimensions as momentum per volume.

Why does Rayl matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Rayl?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Rayl.