Reflection And Refraction Of Light

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SPHERICAL MIRRORSA spherical mirror is a mirror which has the shape of a piece cut out of a spherical surface. There are two types of spherical mirrors:concave, andconvex. he most commonly occurring examples of concave mirrors are shaving mirrors and makeup mirrors. As is well-known, these types of mirrors magnify objects placed close to them. The most commonly occurring examples of convex mirrors are the passenger-side wing mirrors of cars. These type of mirrors have wider fields of view than equivalent flat mirrors, but objects which appear in them generally look smaller (and, therefore, farther away) than they actually are.

Various different types of thin lens

Image Formation by Plane Mirrors

Both concave and convex spherical mirrors asymptote to plane mirrors in the limit in which their radii of curvature $R$ tend to infinity. In other words, a plane mirror can be treated as either a concave or a convex mirror , and Eq.

A concave (left) and a convex (right) mirror

Image formation by a concave mirror.

Spherical aberration in a concave mirror.

Formation of a real image by a concave mirror.

Formation of a virtual image by a concave mirror.

Image formation by a concave mirror

The virtual focus of a convex mirror.

Image formation by a convex mirror.

MagnificationRay diagrams provide useful information about object-image relationships, yet fail to provide the information in a quantitative form. While a ray diagram may help one determine the approximate location and size of the image, it will not provide numerical information about image distance and object size. To obtain this type of numerical information, it is necessary to use theMirror Equationand theMagnification Equation. The mirror equation expresses the quantitative relationship between the object distance (do), the image distance (di), and the focal length (f).

The magnification equation relates the ratio of the image distance and object distance to the ratio of the image height (hi) and object height (ho). The magnification equation is stated as follows:

What is refection?Reflectionis the change in direction of awavefrontat aninterfacebetween two differentmediaso that the wavefront returns into the medium from which it originated. Common examples include the reflection oflight,soundandwater waves. Thelaw of reflectionsays that forspecular reflectionthe angle at which the wave is incident on the surface equals the angle at which it is reflected.Mirrorsexhibit specular reflection. Inacoustics, reflection causesechoesand is used insonar. In geology, it is important in the study ofseismic waves. Reflection is observed withsurface wavesin bodies of water. Reflection is observed with many types ofelectromagnetic wave, besidesvisible light. Reflection ofVHFand higher frequencies is important forradiotransmission and forradar. Evenhard X-raysandgamma rayscan be reflected at shallow angles with special "grazing" mirrors.

Reflection of light is eitherspecular(mirror-like) ordiffuse(retaining theenergy, but losing the image) depending on the nature of the interface. In specular reflection thephaseof the reflected waves depends on the choice of the origin of coordinates, but the relative phase between s and p (TE and TM) polarizations is fixed by the properties of the media and of the interface between them.A mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the reflection actually occurs. Reflection is enhanced in metals by suppression of wave propagation beyond theirskin depths. Reflection also occurs at the surface oftransparentmedia, such as water orglass. pecular reflection formsimages. Reflection from a flat surface forms amirror image, which appears to be reversed from left to right because we compare the image we see to what we would see if we were rotated into the position of the image. Specular reflection at a curved surface forms an image which may bemagnifiedor demagnified;curved mirrorshaveoptical power.


The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.The reflected ray and the incident ray are on the opposite sides of the normal.

Multiple reflections

When light reflects off amirror, one image appears. Two mirrors placed exactly face to face give the appearance of an infinite number of images along a straight line. The multiple images seen between two mirrors that sit at an angle to each other lie over a circle.The center of that circle is located at the imaginary intersection of the mirrors. A square of four mirrors placed face to face give the appearance of an infinite number of images arranged in a plane. The multiple images seen between four mirrors assembling a pyramid, in which each pair of mirrors sits an angle to each other, lie over a sphere. If the base of the pyramid is rectangle shaped, the images spread over a section of atorus.


In this process (which is also known as phase conjugation), light bounces exactly back in the direction from which it came due to a nonlinear optical process. Not only the direction of the light is reversed, but the actual wavefronts are reversed as well. Aconjugate reflectorcan be used to removeaberrationsfrom a beam by reflecting it and then passing the reflection through the aberrating optics a second time.

refractionRefraction is the change in direction of propagation of a wave due to a change in its transmission medium.The phenomenon is explained by the conservation of energy and the conservation of momentum. Due to the change of medium, the phase velocity of the wave is changed but its frequency remains constant. This is most commonly observed when a wave passes from one medium to another at any angle other than 0 from the normal. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth.

Refraction can be seen when looking into a bowl of water. Air has a refractive index of about 1.0003, and water has a refractive index of about 1.3330. If a person looks at a straight object, such as a pencil or straw, which is placed at a slant, partially in the water, the object appears to bend at the water's surface. This is due to the bending of light rays as they move from the water to the air. Once the rays reach the eye, the eye traces them back as straight lines (lines of sight). The lines of sight (shown as dashed lines) intersect at a higher position than where the actual rays originated. This causes the pencil to appear higher and the water to appear shallower than it really is. The depth that the water appears to be when viewed from above is known as the apparent depth. This is an important consideration for spearfishing from the surface because it will make the target fish appear to be in a different place, and the fisher must aim lower to catch the fish. Conversely, an object above the water has a higher apparent height when viewed from below the water.

LAWS OF REFRACTIONIncident ray, reflected ray, refracted ray and the normal of the system lie in the same plane.Incident ray, coming from one medium to the boundary of another medium, is refracted with a rule derived from a physicist Willebrord Snellius. He found that there is a constant relation between the angle of incident ray and angle of refracted ray. This constant is the refractive index of second medium relative to the first medium.

CLINICAL SIGNIFICANCEInmedicine,particularlyoptometry,ophthalmologyandorthoptics,refraction(also known asrefractometry) is a clinical test in which aphoroptermay be used by the appropriateeye care professionalto determine the eye'srefractive errorand the bestcorrective lensesto be prescribed. A series of test lenses in gradedoptical powersorfocal lengthsare presented to determine which provides the sharpest, clearest vision.