Definition

• (i) Light is a form of energy which helps us to see objects.

• (ii) When light falls on objects, it reflects the light and when the reflected light reaches our eyes then we see the objects.

• (iii) Light travels in straight line.• (iv) The common phenomena of light are

formation of shadows, formation of images by mirrors and lenses, bending of light by a medium, twinkling of stars, formation of rainbow etc.

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LOGO Reflection

Reflection of light is either specular (mirror-like) or diffuse (retaining the energy, but losing the image) depending on the nature of the interface. Furthermore, if the interface is between a dielectric and a conductor, the phase of the reflected wave is retained, otherwise if the interface is between two dielectrics, the phase may be retained or inverted, depending on the indices of refraction.

Laws Of Reflection

(i) The angle of incidence is equal to the angle of reflection.

(ii) The incident ray, the reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.

Regular And Diffused Reflection

• Regular Reflection – A smooth surface gives a sharp and clear image. Reflection of light from a smooth mirror is called regular reflection.

• Diffused Reflection – The reflected light falls over a larger area and the image formed is not sharp and clear. This type of reflection is called irregular or diffused reflection.

Real And Virtual Image

• Real Image – a real image is an image in which the outgoing rays from a point on the object pass through a single point. It is easiest to observe real images when projected on an opaque screen (although a screen is not

necessary for the image to form).

• Virtual Image – A virtual image is an image in which the outgoing rays from a point on the object always diverge. It will appear to converge in or behind the optical device (e.g., a mirror). A simple example is a flat mirror where the image of oneself is perceived at

twice the distance from oneself to the mirror.

Kaleidoscope

• A Kaleidoscope operates on the principle of multiple reflection, where several mirrors are together. Typically there are three rectangular lengthwise mirrors. Setting the mirrors at a 60-degree so that it forms a triangle. 60 degree angle apart from each other creates eight duplicate images of the objects, six at 60°, and 2 at 90°. As the tube is rotated, the tumbling of the coloured objects presents varying colours and patterns.

Periscope

• A periscope is an instrument for observation from a concealed position. In its simplest form it consists of an outer case with mirrors at each end set parallel to each other at a 45-degree angle. This form of periscope, with the addition of two simple lenses, served for observation purposes in the trenches during World War I.

• Principle of the periscope. The periscope on the left uses mirrors whereas the right uses prisms.a Mirrorsb Prismsc Observer's eye

Dispersion Of LightDispersion Of Light

• Dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency. Media having such a property are termed dispersive media. Dispersion is sometimes called chromatic dispersion to emphasize its wavelength-dependent nature, or group-velocity dispersion (GVD) to emphasize the role of the group velocity.

Dispersion of sunlight by a prism

The Human Eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the mammalian eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors.

Defects Of Vision

Myopia - Nearsightedness, also called myopia is common name for impaired vision in which a person sees near objects clearly while distant objects appear blurred. In such a defective eye, the image of a distant object is formed in front of the retina and not at the retina itself.

Hypermetropia - Farsightedness, also called hypermetropia, common name for a defect in vision in which a person sees near objects with blurred vision, while distant objects appear in sharp focus. In this case, the image is formed behind the retina.

The Braille System

• Braille is a tactile writing system used by the blind and the visually impaired, and found in books, on menus, signs, elevator buttons, and currency. Braille-users can read computer screens and other electronic supports thanks to refreshable Braille displays. They can write Braille with a slate and stylus or type it on a Braille writer, such as a portable Braille note-taker, or on a computer that prints with a Braille embosser.

Submitted By:-

• Name – Karan Singh Rawat

• Class – VIII

• Section – C• Roll No. - 10