مڪمل اندرين انعڪاس

**مڪمل اندريون انعڪاس** (Total Internal Reflection) اهو طبيعي رجحان آهي جيڪو تڏهن ٿئي ٿو جڏهن روشنيءَ جي هڪ شعاع هڪ شفاف مٿاڇري سان ٽڪرائي ٿي جنهن ۾ هڪ وڌيڪ موج جي رفتار (يعني ڪم درجي جو ريفريڪٽيو انڊيڪس) نازڪ زاويه (Critical Angle) کان وڏي زاويه تي هوندو آهي. اچڻ واري شعاع جي زاوين لاءِ نازڪ زاويه کان وڌيڪ يا برابر، سموري توانائي وقوع واري وچولي طرف ظاھر ٿئي تي.

فزڪس ۾، ڪل اندروني عڪاسي (TIR) ​​اهو رجحان آهي جنهن ۾ هڪ وچولي کان ٻئي تائين (مثال طور، پاڻي کان هوا تائين) انٽرفيس (حد) تي پهچندڙ لهرن کي ٻئي "بيروني" وچولي ۾ داخل ٿينديون آهن، پر اهي مڪمل طور تي واپس پهرين ("اندروني") وچولي ۾ ظاهر ٿينديون آهن. اهو تڏهن ٿئي ٿو جڏهن ٻئي ميڊيم وٽ پهرين کان وڌيڪ موج جي رفتار (يعني ڪم درجي جو ريفريڪٽو انڊيڪس) هجي ۽ لهرون انٽرفيس تي ڪافي ترڪي واري زاويه تي واقع ٿين ٿيون. مثال طور، هڪ عام مڇيءَ جي ٽانڪي ۾ پاڻيءَ کان هوا جي مٿاڇري کي، جڏهن هيٺان کان ٿلهي انداز ۾ ڏٺو وڃي ٿو، پاڻيءَ جي هيٺان منظر کي آئيني وانگر عڪاسي ڪري ٿو، جنهن ۾ روشنيءَ جي ڪا به گهٽتائي ناهي.

"واقعي جو زاويه جنهن جي refraction جو زاويه °90 آهي، ان کي نازڪ زاويه (Critical angle) چئبو آهي." جيڪڏهن هن شعاع جي واقعن جو زاويو اڳتي وڌي ٿو ته پوءِ هي شعاع واپس ساڳي طرف مڙي وڃي ٿو، ان مرحلي تي مڪمل اندروني انعڪاس جو عمل شروع ٿئي ٿو. "جڏهن واقعن جو زاويو (incident angle) نازڪ زاويي کان وڌيڪ آهي، ته شعاع موڙيندي نه آهي، پر سڄي روشني واپس ڳاڙهي وچولي ۾ ظاهر ٿئي ٿي." ان کي کل اندروني عڪاس سڏيو ويندو آهي.

physics, **total internal reflection** (**TIR**) is the phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into the first ("internal") medium. It occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface. For example, the water-to-air surface in a typical fish tank, when viewed obliquely from below, reflects the underwater scene like a mirror with no loss of brightness (Fig.1).

TIR occurs not only with electromagnetic waves such as light and microwaves, but also with other types of waves, including sound and water waves. If the waves are capable of forming a narrow beam (Fig.2), the reflection tends to be described in terms of "rays" rather than waves; in a medium whose properties are independent of direction, such as air, water or glass, the "rays" are perpendicular to  associated wavefronts. The total internal reflection occurs when critical angle is exceeded.

Refraction is generally accompanied by *partial* reflection. When waves are refracted from a medium of lower propagation speed (higher refractive index) to a medium of higher propagation speed (lower refractive index)—e.g., from water to air—the *[[angle of refraction]]* (between the outgoing ray and the surface normal) is greater than the *[[angle of incidence (optics)|angle of incidence]]* (between the incoming ray and the normal). As the angle of incidence approaches a certain threshold, called the *[[#Critical angle|critical angle]]*, the angle of refraction approaches 90°, at which the refracted ray becomes parallel to the boundary surface. As the angle of incidence increases beyond the critical angle, the conditions of refraction can no longer be satisfied, so there is no refracted ray, and the partial reflection becomes total. For visible light, the critical angle is about 49° for incidence from water to air, and about 42° for incidence from common glass to air.

Details of the mechanism of TIR give rise to more subtle phenomena. While total reflection, by definition, involves no continuing flow of power *across* the interface between the two media, the external medium carries a so-called *[[evanescent wave]]*, which travels *along* the interface with an amplitude that falls off exponentially with distance from the interface. The "total" reflection is indeed total if the external medium is lossless (perfectly transparent), continuous, and of infinite extent, but can be conspicuously *less* than total if the evanescent wave is absorbed by a lossy external medium ("attenuated total reflectance"), or diverted by the outer boundary of the external medium or by objects embedded in that medium ("frustrated"&nbsp;TIR). Unlike *partial* reflection between transparent media, total internal reflection is accompanied by a non-trivial phase shift (not just zero or 180°) for each component of polarization (perpendicular or parallel to the plane of incidence), and the shifts vary with the angle of incidence. The explanation of this effect by Augustin-Jean Fresnel, in 1823, added to the evidence in favor of the wave theory of light.

The phase shifts are used by Fresnel's invention, the Fresnel rhomb, to modify polarization. The efficiency of the total internal reflection is exploited by optical fibers (used in telecommunications cables and in image-forming fiberscopes), and by reflective prisms, such as image-erecting Porro/roof prisms for monoculars and binoculars.

**مڪمل اندريون انعڪاس** (Total Internal Reflection) هو طبيعي رجحان آهي جيڪو تڏهن ٿئي ٿو جڏهن روشنيءَ جي هڪ شعاع هڪ شفاف مٿاڇري سان ٽڪرائجي ٿي جنهن ۾ هڪ اعليٰ اضطراب وارو انڊيڪس نازڪ زاويه کان وڏي زاويه تي هوندو آهي. اچڻ واري شعاع جي زاوين لاءِ نازڪ زاويه کان وڌيڪ يا برابر، سموري توانائي واقعي واري وچولي طرف ظاھر ٿئي تي.

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