Hubbry Logo
Angle of incidence (optics)Angle of incidence (optics)Main
Open search
Angle of incidence (optics)
Community hub
Angle of incidence (optics)
logo
7 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Angle of incidence (optics)
Angle of incidence (optics)
from Wikipedia

The angle of incidence, in geometric optics, is the angle between a ray incident on a surface and the line perpendicular (at 90 degree angle) to the surface at the point of incidence, called the normal. The ray can be formed by any waves, such as optical, acoustic, microwave, and X-ray. In the figure below, the line representing a ray makes an angle θ with the normal (dotted line). The angle of incidence at which light is first totally internally reflected is known as the critical angle. The angle of reflection and angle of refraction are other angles related to beams.

In computer graphics and geography, the angle of incidence is also known as the illumination angle of a surface with a light source, such as the Earth's surface and the Sun.[1] It can also be equivalently described as the angle between the tangent plane of the surface and another plane at right angles to the light rays.[2] This means that the illumination angle of a certain point on Earth's surface is if the Sun is precisely overhead and that it is 90° at sunset or sunrise.

Determining the angle of reflection with respect to a planar surface is trivial, but the computation for almost any other surface is significantly more difficult.

Refraction of light at the interface between two media

Grazing angle or glancing angle

[edit]

Focusing X-rays with glancing reflection in a Wolter telescope

When dealing with a beam that is nearly parallel to a surface, it is sometimes more useful to refer to the angle between the beam and the surface tangent, rather than that between the beam and the surface normal. The 90-degree complement to the angle of incidence is called the grazing angle or glancing angle. Incidence at small grazing angles is called "grazing incidence."[citation needed]

Grazing incidence diffraction is used in X-ray spectroscopy and atom optics, where significant reflection can be achieved only at small values of the grazing angle. Similarly, a Wolter telescope used for X-ray astronomy is based on the principle of total external reflection at small graze angles. Moreover, ridged mirrors are designed to reflect atoms coming at a small grazing angle, usually measured in milliradians. In optics, there is Lloyd's mirror.

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia
from Grokipedia
In , the angle of incidence is defined as the angle between an incident and the normal (a line perpendicular to the surface) at the point where the ray strikes the surface. This angle, typically denoted as θi\theta_i, is a fundamental in the interaction of with interfaces between media, such as air-glass boundaries or mirror surfaces. The angle of incidence plays a central role in the law of reflection, which states that the angle of reflection θr\theta_r equals the angle of incidence, ensuring that rays bounce off smooth surfaces predictably. This equality holds for on polished surfaces like mirrors, where the incident, reflected, and normal rays all lie in the same plane, enabling applications in optical devices such as telescopes and periscopes. On rough surfaces, however, scatters in multiple directions, reducing the prominence of a distinct angle of reflection. In , the angle of incidence determines how bends when passing from one medium to another due to a change in speed, governed by : n1sinθi=n2sinθtn_1 \sin \theta_i = n_2 \sin \theta_t, where n1n_1 and n2n_2 are the refractive indices of the respective media, and θt\theta_t is the angle of transmission (or ). This law explains phenomena like the apparent bending of objects viewed through water or lenses, and it defines critical angles leading to when θi\theta_i exceeds a threshold value, essential for fiber optics and prisms. The behavior at interfaces also depends on polarization and the magnitude of θi\theta_i, influencing reflection coefficients for s- and p-polarized .

Fundamentals

Definition

In , the angle of incidence is defined as the angle between an incident and to the interface surface at the point of incidence. This angle, commonly denoted as θ_i, quantifies the orientation of the incoming light ray relative to the surface and is typically measured in degrees or radians. The normal line serves as the reference for this measurement, defined as the straight line perpendicular to the surface at the exact point where the ray strikes. This geometric concept applies specifically to the interaction of rays with boundaries or interfaces between different media, such as air and , where the ray's direction changes upon encounter. In geometric , which treats as propagating in straight-line rays, the angle of incidence provides a fundamental parameter for analyzing how behaves at these junctions, independent of effects. The term and its geometric basis were formalized in 17th-century , notably by in his 1637 treatise La Dioptrique, where he used it to describe ray paths in , and by in his 1662 principle of least time, which incorporated incidence angles to derive optical laws. A typical ray diagram illustrates this by depicting an incident ray approaching a flat interface from one medium, with drawn as a dashed vertical line at the incidence point; the angle θ_i (between 0° and 90°) is then the angle formed between the ray and this normal, often highlighted for clarity.

Relation to Other Angles

In optics, the angle of reflection, denoted as θr\theta_r, is defined as the angle formed between the reflected ray and the normal to the interface at the point of incidence. This angle exhibits a key symmetry with the angle of incidence θi\theta_i, such that θr=θi\theta_r = \theta_i, which underpins the behavior of light upon reflection from a surface. For light transmission across an interface, the angle of refraction, denoted as θt\theta_t, is the angle between the refracted ray and the normal to the surface. This angle describes the deviation of the transmitted ray relative to the incident direction and normal. Standard notation in geometric employs subscripts to distinguish these angles: ii for incidence, rr for reflection, and tt for transmission (or ). This convention facilitates clear communication of ray paths in diagrams and equations. In vector-based representations, the angle of incidence is computed via the of the incident ray's unit direction vector di\vec{d_i}
Add your contribution
Related Hubs
User Avatar
No comments yet.