Angle of incidence: Difference between revisions
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[[Image:Angle of incidence.svg|thumb|Angle of incidence]] |
[[Image:Angle of incidence.svg|thumb|Angle of incidence]] |
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'''Angle of incidence''' is a measure of deviation of something from "straight on", for example: |
'''Angle of incidence''' is a measure of deviation of something from "straight on", for example: |
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| ⚫ | * in the 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, rather than that between the beam and the [[surface normal]], in other words 90° minus the angle of incidence. This angle is called a '''glancing angle''' or '''grazing angle'''. Incidence at small grazing angle is called "grazing incidence". |
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* in the approach of a [[ray (optics)|ray]] to a surface, or |
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* the angle at which the [[wing]] or [[Stabilizer (aircraft)|horizontal tail]] of an [[airplane]] is installed on the [[fuselage]], measured relative to the axis of the fuselage. |
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==Optics== |
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In [[geometric optics]], the angle of incidence is the angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the [[surface normal|normal]]. The ray can be formed by any wave: [[light wave|optical]], [[sound wave|acoustic]], [[microwave]], [[X-ray]] and so on. In the figure above, the red 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. |
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===Grazing angle=== |
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| ⚫ | 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, rather than that between the beam and the [[surface normal]], in other words 90° minus the angle of incidence. This angle is called a '''glancing angle''' or '''grazing angle'''. Incidence at small grazing angle is called "grazing incidence". |
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Grazing incidence is used in [[X-ray spectroscopy]] and [[atom optics]], where significant reflection can be achieved only at small values of the grazing angle. [[Ridged mirror]]s are designed for reflection of atoms coming at small grazing angle. This angle is usually measured in [[milliradian]]s. |
Grazing incidence is used in [[X-ray spectroscopy]] and [[atom optics]], where significant reflection can be achieved only at small values of the grazing angle. [[Ridged mirror]]s are designed for reflection of atoms coming at small grazing angle. This angle is usually measured in [[milliradian]]s. |
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Revision as of 02:49, 4 March 2010
 | This article needs additional citations for verification. (September 2009) |
Angle of incidence is a measure of deviation of something from "straight on", for example:
- in the 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, rather than that between the beam and the surface normal, in other words 90° minus the angle of incidence. This angle is called a glancing angle or grazing angle. Incidence at small grazing angle is called "grazing incidence".
Grazing incidence is used in X-ray spectroscopy and atom optics, where significant reflection can be achieved only at small values of the grazing angle. Ridged mirrors are designed for reflection of atoms coming at small grazing angle. This angle is usually measured in milliradians.
Angle of incidence of fixed-wing aircraft
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On fixed-wing aircraft, angle of incidence is the angle between the chord line of the wing where the wing is mounted to the fuselage and the longitudinal axis of the fuselage. The angle of incidence is fixed in the design of the aircraft by the mounting of the wing to the fuselage.
The term can also be applied to horizontal surfaces in general (such as canards or horizontal stabilizers) for the angle they make relative the longitudinal axis of the fuselage.
The figure to the right shows a side view of an aeroplane. The extended chord line of the wing root (red line) makes an angle with the longitudinal axis (roll axis) of the aircraft (blue line). Wings are typically mounted at a small positive angle of incidence, to allow the fuselage to be "flat" to the airflow in normal cruising flight. Angles of incidence of about 6° are common on most general aviation designs.
Other terms for angle of incidence in this context are rigging angle and rigger's angle of incidence. It should not be confused with the angle of attack, which is the angle the wing chord presents to the airflow in flight. Note that some ambiguity in this terminology exists, as some engineering texts that focus solely on the study of airfoils and their medium may use either term when referring to angle of attack. The use of the term "angle of incidence" to refer to the angle of attack occurs chiefly in British usage.[1]
See also
- Effect of sun angle on climate
- Reflection (physics)
- Refraction
- Season
- Snell's law
- Total internal reflection
Notes
- ^ Kermode, A.C. (1972), Mechanics of Flight, Chapter 3, 8th edition, Pitman Publishing, London. ISBN 0 273 31623 0