(From the Greek isos, "equal" + -tropos, "turning") Having physical properties, as conductivity, elasticity, etc., that are the same regardless of the direction of measurement. For example, metals are isotropic, because their physical properties, such as conductivity and tensile strength, are the same throughout. A liquid is isotropic, but a crystalline solid is not, as it has crystal axes.

Compare: anisotropic
Perhaps an example would be helpful with Isotropic.

A theoretical antenna that can radiate radio frequencies equally in all directions, just like an ever-expanding perfectly spherical ball of energy, is an Isotropic Antenna. In practice, there can not be a physical isotropic antenna because you would have to take into account the feed cable to get the signal to the antenna (which adds electrical impedance, distortion of the field, etc.), the way the earth's surface distorts the radiation pattern, and so forth.

Invariant upon rotation.

For example, neglecting external contamination such as the Earth's magnetic field or the Coriolis effect, physics (or chemistry, biology, etc.) experiments should give the same results regardless of the orientation of the apparatus.

BTW: The observation that the cosmic microwave background of the early universe looks isotropic is a strong piece of evidence in support of the big bang theory and cosmological inflation.

Isotropic minerals are those which belong to the isometric crystal system.

These minerals have three mutually perpendicular crystallographic axes, all of equal length. This causes the light to encounter the exact same atomic environment no matter which direction it travels through the mineral, which unlike in anisotropic minerals, means the light travels at the same velocity in every direction through the mineral.

Viewing Isotropic Minerals with a Petrographic/Polarizing Microscope:

When light travels at the same velocity in each direction, there is no birefringence, so the minerals stays extinct (black) upon rotation under cross polarized light. This is because under crossed polars, all unchanged light is blocked out, and isotropic minerals allow the light to propagate through with out change. This is an identifying characteristic of isotropic (and therefore isometric) minerals. However, there are some angles at which anisotropic minerals can be cut that will cause them to display this behaviour, so many crystal orientations must be observed.

When viewed under plane polarized light, an isotropic mineral will display even relief upon rotation (meaning its outlines look the same no matter the orientation), since its refractive index (how it bends light) is the same in every direction. Again, anisotropic minerals oriented in specific ways can display this behaviour.

Since total extinction is observed, no interference figure can be obtained from an isotropic mineral.

I`so*trop"ic (?), a. [Iso- + Gr. a turning, fr. to turn.] Physics

Having the same properties in all directions; specifically, equally elastic in all directions.


© Webster 1913.

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