lenses introduction.pptx

This is introduction of lenses one of the chapters of 1st year physics

1. CHAPTER # 10 Geometrical Optics .

2. My Topics are: Lenses Real & Virtual Image Rules for image formation

3. Geometrical Optics Geometrical Optics also called Ray Optics is a branch of optics that deals with the study of propogation of light as rays and behaviourral Petterns of light when passing through any medium.

4. Behaviours of light as wave are:

5. Lens : Lens a transparent material such as glass bounded by two surfaces at least one of which is curved is calked a LENS . It has Tedency to Refract the light.

6. What is Refration of light ? It is the phenomenon in which light changes its direction & speed while traves from one medium to the other.

7. Terms RELAted to lens : Optical Center: The center of the lens is called Optical center. Principal Axis: A straight line joining the center of curvature of two sperical surfaces of lens is called Principal Axis . Center of Curvature: The center of the sphere from which a curved surface is obtained is called Center of Curvature Denoted by “C”

8. Pole : The points where the principal axis meet the two surfaces of lens. The Distance between two poles of lens is thickness of lens. Focal Point : It is a point in a focal plane at which all the light rays when coming from a direction and passing through the lens meet together. Focal Length : It is a distance of principal focus from Optical centers Denoted By ‘f’

9. There Are two types of lenses : Convex Lens (Converging lens) Concave Lens ( Diverging lens)

10. Convex lens: The Convex lenses are thicker in the center & thinner at the edges. It is also called converging lens because it converges the parallel beam of light passing through it. The focal length of convex lens is taken to be positive . Convex lens can form both Real and Virtual images. When the object is placed with in the focal length of lens it produces a virtual image and at other positions it forms a Real and Inverted image

11. Kinds of Convex lens: Bicovex :- A lens in which both sides are convex. Plano-convex :- A lens in which one side is convex and the other is plano. Concavo-convex :- A lens where one side is convex & the other concave.

12. Concave Lens: The Concave lenses are thinner at the center & thicker at the edges. It is also called diverging lens because it diverges the parallel beam of light passing through it. The focal length of concave lesn is taken to be negative . It forms a Virtual and Erect image always.

13. Kinds of concave lens: Biconcave :- A lens in which both sides are concave. Plano-concave :- A lens in which one side is concave and the other is plano . Convexo-concave :- A lens where one side is concave & the other concave.

14. Refraction for converging lens It is a refracting law that when light travels from rare to Denser medium it move toward normal line and when light travel from Denser to Rare medium it move away from normal line. This Law is also applied to converging and Diverging lens.

15. Refraction for Diverging Lenses

16. Uses of lens: Lenses are used in various imaging device like telescope, binoculars and cameras. They are also used as visual aids, in glasses to correct defects of vision such as myopia and hypermetropia.

17. What is image ?? In optics an image is defined as the collection of focus points of light rays coming from an object. There are two types of image. Real image Virtual image

18. Real image If the rays of light actually intersect each other after passing through the lens, then the image is called the Real Image . A real image is always Inverted It can be obtained on screen. Real image found in only convex lens.

19. Virtual image If the rays of light appear to intersect each other after passing through a lines, then image is called Virtual Image. It is always Erect. Virtual image can’t be obtained on screen. Virtual image can be found in Convex lens, & concave lens

20. Graphical construction of images by using ray diagrams In order to understand the principle of image formation, we make use of graphic constructions, We known thar an object seatters light falling on it in all direction but for the purpose of locating its image only those rays are considered which pass through the lens. In the following we use ray diagrams to determine the location anf size of the image. Lets consider three rays.

21. The ray 1 leaving the Tip of the object parallel to the axis is refracted by the lens so that it passes through the principal focus F on the other side of the lens. The ray 2 passing through the principal focus F emerges from the lens parallel to the axis. The ray 3 passing through the object center of the lens remain unchanged in the direction.

22. When convex lens fo real image

23. When image is form by Concave lens

24. Image Formation of convex lens