You have already learnt that light is a form of energy. Light enables us to see things. It travels in a straight line. The speed of light is about 300 million (3×10^8) meres per second.
Light travels 8-minutes and 20-seconds to touch the earth’s surface from the sun. The sun is the main source of light that passes through transparent material (such as water, glass, etc). Partially passes through translucent materials and does not pass through opaque materials.
If an opaque body is placed in the path of light, a shadow is formed. This property of light leads us to the idea that light travels in a straight line.
REFLECTION OF LIGHT
If the light is traveling through a medium and it strikes the surface of another medium, a part of it is thrown back along a particular direction in the same medium. This phenomenon is called the Reflection of light.
Mirror and highly polished opaque surfaces reflect light strongly. The reflection follows certain laws. These are discussed below:
(1) Fix a white paper on a drawing board with the help of thumb pins.
(2) Set up a plane mirror on the line XY Vertically with the help of the wooden blocks.
(3) Now fix two pins A and B Vertically in front of the mirror at about 5 cms from each other such that the line joining A and B meets the mirror obliquely as shown in the figure.
(4) Look at the images of pins A and B in the mirror by moving the eyes towards the right. Now fix two ore pins C and D in such a way that the two pins C and D and the images of pins A and B are seen in the same straight line.
(5) Remove all the pins and mirrors after marking their positions in small circles.
(6) Join A, B, and C, D by straight lines and produce them to meet XY at Point O.
(7) Line ABO represents the incident ray, whereas OCD represents the reflected ray, and O is the point of incidence.
(8) Draw a normal OE to the line XY at point of incidence O.
(9) Measure of angle AOE and EOD with the help of a protractor. You would find that the measure of these angles is equal to each other.
(10) The angle AOE which the incident ray makes with the normal is called the angle of incidence.
(11) The angle EOD which the reflected ray makes with the normal is called the angle of reflection.
Whenever a ray is reflected from the place’s smooth surface, the following laws are found to be observed.
(1) The angle of incidence is equal to the angles of reflection.
(2) The incident radiation, the reflected ray, and the normal all lie in the same plane.
REGULAR AND IRREGULAR REFLECTION
(1) When parallel rays of light fall on a smooth and polished surface such as a plane mirror, they are reflected in such a way that the image of the source of light can be seen clearly. Such reflection is called regular reflection.
(2) When parallel rays of light fall on an irregular or rough surface. They will make different angles of incidence at different places. It will also be reflected in different places. It will also be reflected at different angles of reflection and no clear image will be seen. This type of reflection is called irregular reflection.