Chapter: Light
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Light is a form of energy given out by a self luminous body, which travels into infinite media. Light makes things around us visible. Objects that do not give out light of their own are called non-luminous objects. They just reflect light that falls on them. We see with our eyes. When light reflected from an object enters our eyes, the object becomes visible. A mirror changes the direction of light that falls on it. The light ray that falls on a mirror is called the incident light ray. The ray that comes back from the surface after reflection is called the reflected light ray. The point where the incident ray strikes the reflecting surface is called the point of incidence. A line drawn perpendicular to the mirror at the point of incidence is the normal. According to the laws of reflection, the incident ray, the normal at the point of incidence, and the reflected ray lie in the same plane; and the angle of incidence is equal to the angle of reflection.
Light rays are visualised as parallel rays. If the rays, after reflection from a surface, are parallel, then the reflection is termed as regular reflection. The reflection from a plane mirror is an example of regular reflection. When parallel rays, after reflection from a surface, are not parallel, then it is called diffused reflection or irregular reflection. The reflection from an uneven surface is diffused reflection. If a reflected light ray is reflected again on being incident on another surface, it is termed multiple reflections. Multiple reflections are used in periscopes. Periscopes are used in submarines, war tanks and by solders in bunkers to see objects that are not visible directly. In a barber’s shop, we see the back of the head using multiple reflections of two mirrors. In a kaleidoscope, beautiful patterns are formed due to multiple reflections.

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