CHAPTER- 13 LIGHT
NOTES
1. We can see an object only when the light coming from it enters our eyes. This light may either be emitted by the object or reflected from it.
1. Incident Ray- The light ray that falls on a surface is called the incident ray.
2. Reflected Ray- The light ray that bounces back after reflection from a surface is called the reflected ray.
- The line that forms a 90° angle with the mirror at the point where the incident ray strikes is called the normal at that point on the reflecting surface.
3. The angle between the incident ray and the normal is called the angle of incidence.
4. The angle between the reflected ray and the normal is called the angle of reflection.
- The angle of incidence is always equal to the angle of reflection. This is one of the laws of reflection.
- The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane. This is another law of reflection.
5. In the image formed by a mirror, the left side of the object appears on the right, and the right side appears on the left. This phenomenon is called lateral inversion.
6. Regular and Diffused Reflection-
A. Diffused Reflection– When all parallel rays, after being reflected from a rough or irregular surface, are not parallel to each other, such reflection is called diffused reflection.
B. Regular Reflection– In contrast to diffused reflection, the reflection that occurs from smooth surfaces like mirrors is called regular reflection.
- Almost all the objects around us are visible to us due to the reflected light. Example- the moon reflects the light received from the sun.
7. Luminous Object- An object that shines with the light of other objects is called a luminous object.
8. Illuminated Object- An object that emits its own light is called a luminous object.
9. Periscope- A periscope uses two flat mirrors, allowing you to see objects that cannot be viewed directly by reflecting light off the mirrors. Periscopes are used in submarines, tanks, and by soldiers hiding in bunkers to observe objects outside.
10. Kaleidoscope- The concept of multiple reflections formed by mirrors placed at an angle to each other is used in a kaleidoscope to create various attractive patterns.
- An interesting feature of the kaleidoscope is that you will never see the same pattern again.
- Structure of Our Eyes: The shape of our eyes is almost spherical. The outer covering of the eye is white.
- The transparent front part of the eye is called the cornea. Behind the cornea, we find a dark-colored muscular structure called the iris. The iris contains a small opening called the pupil.
- The sclera is the part of the eye that gives it its distinctive color.
- Behind the pupil, there is a lens that is thick at the center. The lens focuses light onto a layer at the back of the eye. This layer is called the retina. The retina is made up of numerous nerve cells.
- There are two types of nerve cells- 1. Cones, which are sensitive to bright light, 2. Rods, which are sensitive to dim light.
- At the junction of the optic nerve and the retina, there are no nerve cells. This point is called the blind spot.
- The image on the retina remains for about 1/16 of a second.
- The most convenient distance for reading with the normal eye is approximately 25 cm.
11. Eye Care-
- If advised by an eye specialist, use appropriate glasses.
- Both too little and too much light are harmful to the eyes. Insufficient light can cause eye strain and headaches. Excessive bright light from the sun, a powerful lamp, or a laser torch can damage the retina.
- Never look directly at the sun or any powerful light source.
- Never rub your eyes. If a dust particle enters your eyes, rinse them with clean water. If there is no improvement, consult a doctor.
- Always keep reading materials at a normal viewing distance. Do not bring your book too close to your eyes or hold it too far away.
12. Cataract- Sometimes, especially in old age, vision becomes blurry. This happens due to clouding of the eye's lens. When this occurs, it is said that a cataract is developing in the eye. To correct this defect, the opaque lens is removed and a new artificial lens is implanted.
- A deficiency of vitamin A in the diet is responsible for many eye diseases. The most common of these is night blindness.
13. Braille System- The most popular method for visually impaired individuals is called Braille.
- Louis Braille, who was himself visually impaired, developed a system for visually impaired individuals and published it in 1821.
- A visually impaired person begins learning the Braille system with letters. After that, they recognize special prints and combinations of letters. Braille texts can be prepared by hand or using a machine.
