Notes
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Topics to be learn :
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Reflection of light : When light rays fall on an object, their direction changes and they turn back. This is called the reflection of light.
Incident ray : A ray of light falling on a surface is called an incident ray.
Point of incidence : The point at which the incident ray strikes the surface is called the point of incidence.
Normal : The perpendicular to a surface at the point of incidence is called the normal.
Reflected ray : The ray of light that leaves the surface at the point of reflection (the same as the point of incidence) is called the reflected ray.
The angle between the incident ray and the normal is called the angle of incidence.
Angle of reflection : The angle between the reflected ray and the normal is called the angle of reflection.
Laws of reflection of light : There are three laws of reflection.
- The angle of reflection is equal to the angle of incidence.
- The incident ray, the reflected ray and the normal lie in the same plane.
- The incident ray and the reflected ray are on the opposite sides of the normal.
Regular reflection of light: The reflection of light from a plane and smooth surface is called regular reflection of light. When the reflecting surface is plane and smooth, the angles of incidence (i) as well as of reflection (r) are the same for all parallel rays incident on the surface. If i1, i2, i3, are the angles of incidence for incident parallel rays, and r1, r2, r3, are the corresponding angles of reflection, then, i1 = i2 = i3 =…. = r1 = r2 = r3 =… This is called regular reflection Here the reflected rays are parallel to one another
Irregular reflection of light : The reflection of light from a rough surface is called irregular reflection of light. If the reflecting surface is rough and parallel rays are incident on it, then the angles of incidence are not equal and hence the angles of reflection are also not equal. Here, for parallel rays of light falling on the surface, i1 ¹ i2 ¹ i3…, and i1 = r1 ¹ r2 ¹ r3.
| Remember :
1. Laws of reflection are followed in both regular and irregular reflection. 2. The reflection of light in irregular reflection has not been obtained because the laws of reflection are not followed but they are obtained because the surface is rough. (irregular). 3. In irregular reflection the angles of incidence at different points are different. But at any one point, the angles of incidence and reflection are equal, i.e i1=r1, i2=r2,... |
Kaleidoscope : The working of a kaleidoscope is based on the reflection of reflected light. In a kaleidoscope, three plane mirrors are fixed at 60° with each other. Hence, the rays of light starting from an object (reflected rays) are reflected many times by the mirrors, thereby forming many images.
Periscope : The working of a kaleidoscope is based on the reflection of reflected light. The two mirrors in a periscope are placed parallel to each other so that the rays of light emerging out of the periscope are parallel to the rays incident on the top window of the periscope and hence the location of the object can be seen clearly. See Fig. Use : A periscope is used on a submarine to keep a watch on things above the surface of the sea even when the submarine is under water.
