The laws list
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R to Rydberg formula.
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R.
R
See ideal gas constant.
radian; rad
The supplementary SI unit of angular measure, defined as the central angle of a circle whose subtended arc is equal to the radius of the circle.
Rayleigh-Jeans law

For a blackbody at thermodynamic temperature T, the radiancy R over a range of frequencies between nu and nu + dnu is given by

R = 2 pi nu2 k T/c2.

Compare Planck radiation law; see ultraviolet catastrophe.

Rayleigh criterion; resolving power
A criterion for determining how finely a set of optics may be able to distinguish. It begins with the assumption that central ring of one image should fall on the first dark ring of the other; for an objective lens with diameter d and employing light with a wavelength lambda (usually taken to be 560 nm), the resolving power is approximately given by
1.22 lambda/d.
reflection law
For a wavefront intersecting a reflecting surface, the angle of incidence is equal to the angle of reflection, in the same plane defined by the ray of incidence and the normal.
refraction law
For a wavefront travelling through a boundary between two media, the first with a refractive index of n1, and the other with one of n2, the angle of incidence theta is related to the angle of refraction phi by
n1 sin theta = n2 sin phi.
relativity principle
The principle, employed by Einstein's relativity theories, that the laws of physics are the same, at least qualitatively, in all frames. That is, there is no frame that is better (or qualitatively any different) from any other. This principle, along with the constancy principle, constitute the founding principles of special relativity.
resolving power
See Rayleigh criterion.
right-hand rule
A trick for right-handed coordinate systems to determine which way the cross product of two 3-vectors will be directed. There are a few forms of this rule, and it can be applied in many ways. If u and v are two vectors which are not parallel, then u cross v is a vector which is directed in the following manner: Orient your right hand so that your thumb is perpendicular to the plane defined by the vectors u and v. If you can curl your fingers in the direction from vector u to vector v, your thumb will point in the direction of u cross v. (If it doesn't, the vector is directed in the opposite direction.) This has immediate application for determining the orientation of the z-axis basis unit vector, k, in terms of the x- and y-axes' basis unit vectors; curl your right hand in the direction of i to j, and your thumb will point in the direction of i cross j = k.

The rule is also applicable in several practical applications, such as determining which way to turn a screw, etc. There is also a left-hand rule, which exhibits opposite chirality.

Roche limit
The position around a massive body where the tidal forces due to the gravity of the primary equal or exceed the surface gravity of a given satellite. Inside the Roche limit, such a satellite will be disrupted by tides.
Rydberg constant (Rydberg)
A constant which governs the relationship of the spectral line features of an atom through the Rydberg formula. For hydrogen, it is approximately 1.097 x 107 m-1.
Rydberg formula (Rydberg)
A formula which describes all of the characteristics of hydrogen's spectrum, including the Balmer, Lyman, Paschen, Brackett, and Pfund series.

For the transition between an electron in orbital m to one in orbital n (or the reverse), the wavelength lambda involved is given by

1/lambda = R (1/m2 - 1/n2).
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