Light is a type of energy that is transmitted in the form of electromagnetic waves, which humans know through the eyes. The wavelength of light is between 3900 Angstrom to 7800 Angstrom. Let us display the Angstrom from A.
A = 1010 m (where m = m)
- Natural sources of light are the sun, stars, and other light sources of space.
- Earth receives energy from the Sun at a rate of about 4 × 10 26 joules per second.
- The light received from living animals is called bio-light.
- Light is a type of transverse wave. Roemer first counted Prakash. The velocity of light in vacuum and air is 3 × 108 meters per second, which is the highest.
- It takes about 8 minutes 20 seconds for sunlight to reach the earth.
- The moon has no light of its own. The moon is illuminated by sunlight. It takes 1.28 seconds for the reflected light from the moon to reach the earth.
- The speed of light depends on the refractive index of the medium. The higher the refractive index of the medium, the lower the speed of light in it.
- The speed of light is highest in air and vacuum.
Light Speed in Different Medium
|Medium||Speed of Light (in meters per second)|
|Water||2.25 × 10^8|
|Glass||2 x 10^8|
|Vacuum||3 x 10^8|
|Nylon||2.99 x 10^8|
|Turpentine Oil||2.04 x 10^8|
Reflection of Light
The phenomenon of a light beam hitting a smooth surface and returning back is called Reflection of Light.
Reflection of Light has two laws –
- The incident ray has a normal and reflected ray in the same plane at the point of incidence.
- The angle of incidence is equal to the angle of reflection.
Reflection of Light by Plane Mirror
A plane mirror is the best reflector of light. The perpendicular straight line of the reflected surface is called the normal.
A ray falling directly on the reflecting plane is called an incident ray.
A ray that returns back to the same medium after reflection is called a reflected ray.
In a plane mirror, the image of an object is formed behind the plane mirror at the same distance as the object is placed in front of the plane mirror. The image is imaginary, equal to the object, and is inverted.
To see the full image of an object in a plane mirror, the length of the mirror must be at least half the length of the object.
If a person comes towards the mirror at the speed of V, then he sees his image in the mirror coming towards him with double speed i.e. 2V speed.
If the mirror is rotated by theta degree angle keeping the incident ray fixed, then the reflected beam rotates to theta degree.
If two plane mirrors are inclined at a theta degree angle, then the number of images of the object placed between them will be as follows:
(1) 3600/900 – 1 = 4 – 1 = 3 images will be formed between two plane mirrors bent at 900 angles.
(2) 3600/400 = 9 images will be formed between two plane mirrors bent at 400 angles.
(3) If an object is placed at 200 between two plane mirrors inclined at 400 angle, then the number of images will be 3600/400 – 1 = 9 – 1 = 8.
(4) If 3600 / theta degree is a different number, the number of images will be equal to its integer.
It is clear from the above analysis:
(a) If an even number comes to 3600 / theta degree, then the number of images of the object in all circumstances is (n) = 3600 / theta degree – 1.
(b) If 3600 / theta degree is an odd number, then the number of images of the object is (n) = 3600 / theta degree in all situations.
(c) If 3600 / theta degree is an odd number and the object is placed on the bisector of the angle between the two mirrors, then the image of the object is (n) = 3600 / theta degree – 1.
Law of Reflection Light
- The incident ray, the normal and reflected rays are in the same plane.
- The value of the incidence angle is equal to the angle of reflection.
Total Internal Reflection of Light
If the value of incidence angle is slightly higher than the critical angle, then the light is not able to go into the sparse medium at all, but after reflecting the entire light, it returns to the dense medium itself, the same phenomenon of light is reflected in the total internal reflection of light (Total Internal Reflection of Light).
For example, the sparkling of diamonds, the crackling of a crack in the glass, the formation of a mirage in the desert, and the glowing of a test tube lying in the water, etc.
In this incident of light, refraction of light does not happen at all, the entire incident light gets reflected.
What are the conditions that must be fulfilled for the total internal reflection of light?
For a complete internal reflection of light, the following conditions are absolutely necessary:
- A ray of light is entering the sparse medium.
- The angle of incidence is greater than the critical angle.