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CNMS ICSE - 7 Std
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Key Terms

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Chapter: 04. Light

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Reflection of light: The bouncing back of the rays of light as they strike a surface.
Mirror: A smooth and highly polished surface which reflects most of the light falling on it.
Incident ray: The ray of light which strikes the reflecting surface.
Reflected ray: The ray of light which is reflected back into the same medium after striking a surface.
Point of incidence: The point on the reflecting surface at which the incident ray strikes it.
Normal: A perpendicular line drawn to the reflecting surface at the point of incidence.
Angle of incidence: The angle between the incident ray and the normal.
Angle of reflection: The angle between the reflected ray and the normal.
Plane: The plane containing the incident ray, the reflected ray, and the normal.
Plane mirror: A mirror whose surface is flat, highly polished, smooth, and reflecting.
Lateral inversion: The phenomenon in which the right side of an object appears to be at the left in its image, after reflection, and vice versa.
Periscope: A long, vertical tube containing a set of mirrors that gives you a view of what is above you when you look through the bottom of the tube.
Kaleidoscope: An instrument containing mirrors that is used for producing colourful patterns.
Refractive index: The ratio by which the speed of light is slowed down when it travels through transparent materials such as water and glass.
Primary colours: Colours of light (red, green, and blue) that cannot be obtained by mixing any other colours but can produce other colours when mixed together.
Secondary colours: The colours produced by mixing any two primary colours.
Rainbow: A natural band of colours formed in the atmosphere when white light from the sun passes through tiny water droplets.
Colour subtraction: The process of determining the colour of an object when a beam of light of a single colour or a mixture of colours is thrown on it.
Regular (or specular) reflection: Reflection that occurs when parallel rays of light fall on a smooth surface like that of a mirror, and the reflected rays are also parallel.
Diffused (or irregular) reflection: Reflection that occurs when light is reflected from a rough surface, causing parallel incident rays to be reflected at different angles and in different directions.
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