Diverging Lens

Diverging lens which are thinner in the middle than at the edge
Types of diverging lenses

The symbolize of diverging lenses

The part of diverging Lenses

Construction of rays diagram for diverging lenses

1.      A ray parallel to the principle axis is refracted seemed to the second focal point (F2)

2.      A ray proceeds toward the second focal point (F2) is  refracted parallel to the principle axis

3.      A ray passing trough to the center (C) is not deviated

The image formed by a concave lens not depends on the positions of the object

Thin Lens

A lens is a piece of transparent material. Lenses are the most important practical application of refraction. There are many instruments, which use lenses. We use lenses in spectacles, cameras, telescope and microscopes. The human eye also contains lens.
Most lenses made from glass or clear plastic. In terms of structure and function, we can classify into two categories.
1.Converging lens
Converging lenses which are thicker in the middle than at the edge
Types of converging lenses

The symbolize of converging lenses

 The part of Converging Lenses  

Refractive Index

Refractive Index and Speed of Light
The refractive index, n, of a medium may also be defined as the ratio of the speed of light in a vacuum ( C) to the speed of light in that medium (Cn).
Namely, n = C/Cn

Question
If the speed of light in air is 3.00.000.000 m/sec, find the speed of light in diamond. (Refractive index of diamond = 2,42)

Solution
n       = C/Cn
2,42 = 3,/Cn
Cn   = 3.00.000.000/2,42
       = 124.000.000 m/sec

Note: The higher the refractive index of a medium, the slower will be the speed of light through it. This means that medium’s optical density increase as its refractive index increase.

Refractive Index and Wavelength of Light
The refractive index, n, of a medium may also be defined as the ratio of the wavelength of light in a vacuum (lambda) to the Wavelength of light in that medium
(lamda n). Namely, n = lambda/ lambda n
Question
Monochromatic red light of wavelength 640 nm (nanometer) passes from air into
glass plate of refractive index 1,5. What is the wavelength of this light inside the
glass?
Plan: The wavelength will be less in the glass due to the slower speed of the light.
Solution:
ng = la/ lg
lg = la/ ng
lg = 640/1, 5
= 427 nm
Exercises
1. Sketch rays diagram below!

2. The speed of light in vacuum is 3.00.000.000 m/s. What is the speed of light in a medium whose refractive 

     index  is  1,42?

3. Monochromatic yellow light of wavelength 880 nm passes from air into water. If the wavelength of this 

    light  in water 660 nm, what is the refractive index in water?

REFRACTION

Refraction of light is the bending of a ray of light as it travels from one medium to another. Refraction of light occurs due to change in the speed of light as it travels from one medium to anothe

In 1620, a Dutch scientist Willebrord Snell discovered the relation ship between the angle of incident and the angle of refraction when light travels from one medium to another

The laws of refraction he put together are follows:

1.      The incident ray, the refracted ray and the normal at the point of incident all lie on the  

      same plane

2.      For two given media, the ratio sin i/sin r is a constant 

Investigating the refraction of light through two media

•         When light travel from air into glass or water, it slows down. A medium is said to be optically dense if it reduces the speed of light

•         The following example will help us understand refraction better

1. Light travels from a less dense medium (air) to a denser medium (water), its speed decrease and it is refracted towards the normal 

2.Light travels from a denser medium (glass) to a less medium (water), it is refracted away from the normal

3.Light travels from a denser medium (glass) to a less medium (water), it is refracted away from the normal