#Physics-optics-Reflection and #Refraction-of_light part 1 in Hindi English We see a variety of objects in the world around us. However, we are
unable to see anything in a dark room. On lighting up the room,
things become visible. What makes things visible? During the day, the
sunlight helps us to see objects. An object reflects light that falls on it.
This reflected light, when received by our eyes, enables us to see things.
We are able to see through a transparent medium as light is transmitted
through it. There are a number of common wonderful phenomena
associated with light such as image formation by mirrors, the twinkling
of stars, the beautiful colors of a rainbow, bending of light by a medium
and so on. A study of the properties of light helps us to explore them.
By observing the common optical phenomena around us, we may
conclude that light seems to travel in straight lines. The fact that a small
source of light casts a sharp shadow of an opaque object points to this
#straight_line_path of light, usually indicated as a ray of light.
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Reflection and refraction
Light rays change direction when they reflect off a surface, move from one transparent medium into another, or travel through a medium whose composition is continuously changing. The law of reflection states that, on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray. (By convention, all angles in geometrical optics are measured with respect to the normal to the surface—that is, to a line perpendicular to the surface.) The reflected ray is always in the plane defined by the incident ray and the normal to the surface. The law of reflection can be used to understand the images produced by plane and curved mirrors. Unlike mirrors, most natural surfaces are rough on the scale of the wavelength of light, and, as a consequence, parallel incident light rays are reflected in many different directions, or diffusely. Diffuse reflection is responsible for the ability to see most illuminated surfaces from any position—rays reach the eyes after reflecting off every portion of the surface.
Rays and wavefronts
Light is a very complex phenomenon, but in many situations, its behavior can be understood with a simple model based on rays and wavefronts. A ray is a thin beam of light that travels in a straight line. A wavefront is a line (not necessarily straight) or surface connecting all the light that left a source at the same time. For a source like the Sun, rays radiate out in all directions; the wavefronts are spheres centered on the Sun. If the source is a long way away, the wavefronts can be treated as parallel lines.
Rays and wavefronts can generally be used to represent light when the light is interacting with objects that are much larger than the wavelength of light, which is about 500 nm. In particular, we'll use rays and wavefronts to analyze how light interacts with mirrors and lenses.
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