8th Class Science Light Reflection of Light

       Reflection of Light

When the light is incident on the surface of an object, it is reflected, transmitted,or absorbed. When it falls on the polished surface, it reverts back on the sameplane. This phenomenon is known as reflection of light. In other words,"Bouncing back of the light after striking a polished surface is called reflectionof light".

Silver metal is the best reflector of light, as it reflects all of the light falling onit. It does not transmit or absorb any portion of light received. So an ordinarymirror is made by polishing the surface of glass with the silver paints. If wescratch the paints from the surface, it becomes transparent and light passesthrough it.

           Laws of Reflection of Light

Reflection of light from the plane or spherical surface takes place according tothe laws given below. They are known as the laws of reflection of light.

(a) It states that the incident ray, the reflected ray, and the normal, alllies on the same plane.

(b) The angle of incidence and the angle of reflection are equal.\[\angle i=\angle r\]

Here,\[i\] denotes the angle of incidence and r denotes the angle of reflection.We observe, when the ray of light falls normal to the surface, it is reflectedalong the same path. In such case, the angle of incidence and the angle ofreflection are zero. Anything, which gives off the light or reflects the light iscalled an object. An optical appearance is produced, when the light falls on anobject or reflection produced by an object. Image is of two types:

(i) Virtual                            

(ii)  Real

         Virtual Image

The image that cannot be obtained on the screen are called virtual image. Forexample, the image of our body formed by a mirror is a virtual image. Thisimage cannot be obtained on the screen. A virtual image is formed when thelight ray coming from an object appears to be produced behind the mirror.

           Real Image

The image that can be obtained on the screen is called real image. A realimage is formed when the ray of light coming from an object meets at a pointafter reflection from the mirror. Real image can be formed with the help ofconcave mirror and convex lens. For example, the image formed on the screenof the cinema hall is a real image.

           Transverse Nature of Light

Light always travel in a straight line. If an obstacle is placed in its path, itstops there only. For example, if we switch on the light in a room and close thedoors and windows of the room, the light will not go out side.

Experiments carried over hundred years showed us that the light has dual naturei.e. particle nature as well as wave nature. The Quantum theory of light describesboth of them together. Certain phenomena, such as, interference andpolarization can be explained only by the wave nature of light. On the otherhand, phenomena like reflection, refraction and casting of shadow by an objectcan be explained only on the basis of particle nature of the light.

        If you are sitting in a closed room and switch on the light, the roomwill get illuminated. This light does not go outside the room. Whichone of the following property of light is shown by this observation?

(a) Wave nature

(b) Longitudinal nature

(c) Transverse nature

(d) Particle nature

(e) None of these

Answer: (c)

Explanation

Light travels in a straight line and particles of the light travels in thedirection perpendicular to the direction of the propagation, which isknown as transverse nature of the light.  

         Bravo and Ronald live in the adjacent rooms separated by a wall.There are few holes on the wall through which light can pass. If thelight of one room is switched on and other is switched off then onecan easily see through the hole inside of the other room. But, if thelight of both room are switched on other room appears to be darkthrough the hole. If the two light of equal wavelength issuperimposed, it produces:

(a) Light band

(b) Dark band

(c) Red light

(d) Blue light

(e) None of these

Answer: (b)

         Maria took four metal sheets and place them in the Sun light. Sheobserves that one of the metal sheet showing more reflection, whilethe other showing less reflection. Which one of the following metalsheet will show the maximum reflection?

(a) Gold

(b) Iron

(c) Silver

(d) Platinum

(e) None of these

Answer: (d)

Explanation

The metal, which has polished surface will show maximum reflection.Platinum metal has polished surface, hence shows maximum reflection.  

         Robert and Carlos went to see movie in a cinema hall. They observedthat the beam of light was focused on the screen from behind througha hole, to obtain the images on the screen. What was the nature ofimage on the screen of the cinema hall?

(a) Real

(b) Virtual

(c) Inverted

(d) All of these

(e) None of these

Answer: (a)

Explanation

The image which are obtained on the screen are called real image. Theimage on the screen of cinema is a real image..