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
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)
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 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
1. An object that has 4 cm of height is located 15 cm in front of the concave mirror.
If the focal length of the concave mirror is 10 cm, determine :
a.The distance of image!
b.Magnification of image!
c.Height of image!
d.The characteristics of image!
2. An object that has 5 cm of height is located 60 cm in front of the convex
mirror. If the focal length of the convex mirror is 15 cm, determine :
a.The distance of image!
b.Magnification of image!
c.Height of image!
d.The characteristics of image!
Defining of convex
The convex mirror is the outside of the spherical surface is the reflecting surface.
The characteristic of concave mirror to spread of rays or DIVERGEN
The cut point of focusing reflected rays mentioned FOCUS LENGTH
Special rays of convex Mirror
1. A ray parallel to the mirror axis of a concave mirror seems to come from the
focal point of a convex mirror
2. A ray that passes through the focal point of a concave mirror is reflected parallel
to the mirror axis
3. A ray that proceeds along a radius of the mirror is reflected back original path
Slide 1
nShaping its image if an object is placed in front of the convex mirror
The nature of image is virtual, erect and diminished
The mirror equations can be applied to either concave or convex mirrors
The concave mirror is the inside of the spherical surface is the reflecting surface.
The characteristic of concave mirror to collect of rays or CONVERGEN
The cut point of focusing reflected rays mentioned FOCUS LENGTH
The parts of concave mirror
Slide 11
Explainations of the above figure C = center of mirror curve or radius of curvature
1. Good reflector of light
a. Light ray does not actually pass through the mirror (behind the mirror).
b. It only appears to an observer as through the ray comes behind the mirror 2. The image is a virtual image
a. Virtual image cannot be projected or focused on to a screen
b. Image formed behind the mirror
1. An object is placed at the distance of 10 cm in front of a plane mirror. Then the mirror is move 3 cm a far closer to object.Determine:
a. The distance between an object with its image, before moved
b. The distance between an object with its image, after moved
c. The distance between the first image with the second image
2. Two plane mirrors are pinched together to form an angle of 45 degree. Determine the number of the image formed by both mirrors.
3. Two plane mirrors are pinched together to form certain an angle . If the number of image that happened is 11 image,determine the number of the angle by bothmirrors.
4. Sketch-ray diagram and determine the image nature/property formed by a plane mirror of an object below!
5.Diagram as follows shown image from o’clock in a plane mirror. What time which shown by the o’clock?
The light reflection of laws
1. The Incident ray, The normal line, and reflected ray to the surface at the point
of incidence all lie on the same plane
2. The angle of incident ray equal with the angle reflected ray
In daily life, light has an important role. We can see the object because light is reflected from the object to our eyes. When we looked into the mirror, we will see our image so that we can tidy-up our clothes and hair. Is it possible for us to look our self in the mirror, read a book, or see an object in a dark room?
Light travels in a straight line in a vacuum or uniform medium.
Belajar Fisika bagi sebagian besar siswa masih menjadi momok yang menakutkan, karena sulit. Hal Ini disebabkan rumus yang seharusnya menjadi alat mempercepat perhitungan soal, justru akhirnya mempersulit siswa. Penyelesaian soal fisika menjadi sulit karena anak terbelenggu dengan banyaknya rumus. Ini tidak bisa dimungkiri karena sistem pengajaran fisika di sekolah masih banyak yang berorientasi pada penyelesaian soal dengan rumus. Begitu banyak rumus yang harus dihafal, tetapi anak tidak banyak yang memahami konsep yang diturunkan dalam rumus itu. Metode pembelajaran fisika yang mudah, menarik, dan menantang bagi anak didik merupakan impian bagi setiap guru fisika.
A. Reflection of light
B. Refraction of light
C. Thin lenses
Objectives
Recall and use the terms for reflection, including normal, angle of incidence and angle of reflection.
State that, for reflection, the angle of incidence is equal to the angle or reflection and use this principle in constructions, measurements and calculations
Recall and use the term for refraction, including normal, angle of incidence and angle of refraction.
Define refractive index of a medium in terms of the ratio of speed of light in vacuum and in the medium
Explain the terms critical angle and total internal reflection.
Identify the main ideas in total internal reflection and apply them to the use of optical fibers in telecommunication and state the advantages of their use.
Describe the action of mirror ( both concave and convex) on a beam of light
Describe the action of thin lens ( both converging and diverging) on a beam of light.
Define the term focal length for a converging lens
Draw ray diagram to illustrate the formation of real and virtual images of an object by a thin converging lens
