RRB NTPC Exam 2016 will test you on your knowledge of Light and related phenomena.
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RRB NTPC Exam 2016 #Daily Infographic on General Science (PHYSICS)
Light is all around us. It is the primary way we come to know the universe, and thus is very important to physicists. Until the middle of 1800’s, light was taken to be a stream of tiny particles. This was the stance advocated by Newton. However, by the late 1800’s the particle theory was replaced by the wave theory. This was because light exhibited certain properties that could only be explained by the wave theory.
One of the properties of light is that it reflects off surfaces. Among other things, this reflection allows us to see images in mirrors. Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.
If the reflecting surface is very smooth, the reflection of light that occurs is called specular or regular reflection. The laws of reflection are as follows:
- The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
- The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.
- The reflected ray and the incident ray are on the opposite sides of the normal.
Refraction means that light bends when it passes from one medium to another. When light enters a denser medium from one that is less dense, it bends toward a line normal to the boundary between the two media. The greater the density difference between the two media, the more the light bends. This property is used with respect to optical devices such as microscopes, corrective lenses for vision, magnifying lenses, and so on.
You may have noticed that, when you look into the surface of a lake or pond while fishing, the fish you catch seems larger when under the water than when you actually land it. This is due to refraction. Since the air is less dense than water, the light beds away from the normal as it emerges. Another common example is that your feel look larger and closer to the surface underwater than they really are.
Dispersion is another property of light. This refers to the ability to break white light into its constituent colors. White light consists of all of the colors we are able to see. If white light enters a prism, what emerges from the other side is a spread out beam of multi-colored light. Blue light, with longer wavelengths, gets bent more by the different angles of the prism than red light, and the other colors are in between blue and red on the wave spectrum.
Diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle. Diffraction is the slight bending of light as it passes around the edge of an object. The amount of bending depends on the relative size of the wavelength of light to the size of the opening. If the opening is much larger than the light’s wavelength, the bending will be almost unnoticeable. However, if the two are closer in size or equal, the amount of bending is considerable, and easily seen with the naked eye.
Take the Quiz on Light & Related Properties