Geometrical Optics and Reflection of Light

Edited by Jen Moreau, Sim

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GEOMETRICAL OPTICS

Reflection of Light:

Reflection is the process by which light hits a boundary or a medium and then bounces back.

The amount of reflected light depends on:

  • a. The nature of the medium that propagates through
  • b. The color of light
  • c. The angle at which the light strikes the surface of the boundary.

Some facts about the reflection of light:

  • The light ray that hits the boundary is called incident ray and the ray that bounces back is called reflected ray.
  • When light falls on a plane mirror, about 80% of the incident light is reflected.
  • A black or opaque body is a bad reflector while a white body is a good reflector.
  • From a highly polished surface, nearly all the light is reflected.

Regular Reflection: (Specular reflection) is defined as reflection of light from a smooth surface

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Irregular Reflection: (Diffuse Reflection) Reflection from any rough surface is called irregular reflection or diffuse reflection.

Reflection of Light from A Plane Surface

(Plane Mirror)

  1. 1
    Ray of light:
    A ray of light is the straight line along which light travels.
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  2. 2
    Incident Ray:
    is the ray of light which falls on the mirror surface. In the figure, mm' is the mirror and AO is the incident ray.
    Geometrical Optics and Reflection of Light 99621.jpg
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  3. 3
    Reflected Ray:
    The ray of light that bounces back from the mirror is called reflected ray. In the figure, OB is the reflected ray.
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  4. 4
    Normal:
    The normal is the line that is perpendicular to the mirror at the point of incidence. ON is the normal.
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  5. 5
    Angle of Incidence:
    The angle between the incident ray and the normal is called incident angle. In the figure, AON is the angle of incidence, denoted by 'Li'.
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  6. 6
    Angle of Reflection:
    The angle between the reflected ray and the normal is called reflected angle. NOB is the angle of reflection, denoted by 'Lr'.
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Laws of reflection of Light:

There are two laws that explain reflection of light that was first discovered by the Muslim scientist, Ibn-Ul Haitham. These laws are the following: I. The incident ray, the reflected ray and the normal (at the point of incidence) all lie in the same plane. ii. The angle of incidence (Li) is always equal to the angle of reflection. (Lr) i.e

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mLi = mLr

3 Optics.png

Spherical Mirror

Spherical Mirror 74119.jpg

Mirror: is defined as a surface from which light undergoes regular reflection.It is also defined as the smooth and the polished surface of a medium from where most of light reflects.

Spherical Mirror: is a mirror where either its inner or outer surface is polished to reflect light.

A spherical mirror, as its name implies, has the shape of a segment of a sphere. Spherical mirrors are classified as concave and convex mirrors.

  1. 1
    Concave Mirror:
    is a spherical mirror where the inner side of the shell is polished to reflect light. Example, the inner shining surface of a spoon.
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  1. 1
    Convex Mirror:
    is a spherical mirror with a polished outer side. It diverges a parallel beam of light, therefore it is also called a diverging mirror. The back side of a shining spoon is an example of a convex mirror.
    Geometrical Optics and Reflection of Light 19230.jpg
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Uses of spherical Mirrors:

Spherical mirrors have different uses:

  1. 1
    As Shaving Mirrors:
    Concave mirrors are used as a shaving mirror. When a person looks through this mirror, the enlarged, virtual and erect image of his face will be seen in the mirror, thus helping him make a clean and neat shave.
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  2. 2
    For Medical Use:
    Concave mirrors are used by doctors for the medical examination of ear, nose, and throat (ENT Doctors). They are also used by dentists to examine backside of the tooth.
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  3. 3
    In Microscope:
    concave mirrors are used in a microscope to concentrate light on a microscopic slide.
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  4. 4
    Automobiles:
    Concave mirrors are used in car head lights, search lights, and spot lights.
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  5. 5
    To observe Rear view:
    convex mirrors are used in vehicles to observe rear view. It makes small, erect and virtual images of the object behind the vehicle. Convex mirrors are also used in dangerous roads to avoid accidents especially in sharp turns on hillsides.
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Referencing this Article

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APA (American Psychological Association)
Geometrical Optics and Reflection of Light. (2017). In ScienceAid. Retrieved Mar 25, 2017, from https://scienceaid.net/Geometrical_Optics_and_Reflection_of_Light

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MLA (Modern Language Association) "Geometrical Optics and Reflection of Light." ScienceAid, scienceaid.net/Geometrical_Optics_and_Reflection_of_Light Accessed 25 Mar 2017.

Chicago / Turabian ScienceAid.net. "Geometrical Optics and Reflection of Light." Accessed Mar 25, 2017. https://scienceaid.net/Geometrical_Optics_and_Reflection_of_Light.

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Categories : Physics

Recent edits by: Jen Moreau

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