Light is a form of energy that enables us to see all the things around us. The main source of light on the earth is the sun. The light reflection is the returning of light waves in the same medium on meeting a reflecting surface. We see things only when light coming from them enters our eyes. So we will learn about the structure of the eyes. We will also learn about the primary defects in vision and how they can be corrected by wearing a suitable glass. Further in the chapter, we will study the periscope is a long, tubular device through which a person can see objects that are out of the direct line of sight.

We have already learned about the laws of reflection in the previous class. Now we will study it in more detail. The law of reflection states that the angle of incidence is equal to the angle of reflection. So, in this virtual tour, we will explore that when a torchlight strikes on the mirror, it reflects back in a particular direction.

The light reflection is classified according to the nature of the reflecting surface into the regular reflection, and the irregular reflection.  The regular reflection takes place when light is incident on smooth, polished, and regular surfaces. Diffused or irregular reflection takes place from rough surfaces. 

There are two plane mirrors used in the periscope. Periscope works on the two plane mirrors arranged parallel to one another. It is used in submarines to see what is going on the water surface. The periscopes on submarines may be as long as 18 meters. And using this periscope we are able to see the object which is outside of the submarine, without coming out from the submarine.

We see things only when light coming from them enters our eyes. The eye is one of our most important organs. Now we will understand the structure and functioning of the eye. Parts of the eye are the cornea, iris, pupil, lens, retina, and optic nerve. And, a human eye can see nearby and distant objects clearly. 

For a normal vision, the near point is 25 cm and the far point is at infinity. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. Myopia (short-sightedness – the image of distant objects is focused before the retina) is corrected by using a concave lens of suitable power.  

We will learn about Hypermetropia which is also called hyperopia. A hyperopic person can only see the far objects clearly and nearby objects appear blurry. So it is also called farsightedness. It is corrected by using a convex lens of suitable power.

In presbyopia, the eye loses its power of accommodation at old age. It is a normal part of aging and can happen to anyone, even those with no provision problem. However, the condition can be easily corrected. This defect can be corrected by using a bifocal lens.