It is used for correction of hypermetropia and presbyopia. Case 1: Object at infinity A point object lying on the principal axis: Rays come parallel to the principal axis and after refraction from the lens, appears to come from the second principal focus F2. Where should be the position of the object? Image formation in convex lens Case 1:When object beyond 2F: In this case image will form between F and 2F, image will be real, inverted, smaller than the object. Case 5: Object at Focus Real object AB has its image formed at infinity. Image of foot is formed at focus. These diverged rays i.e. Convex lens : big size object at infinity, image at focus. Therefore, in case of concave lens when the object is placed at infinity the image is formed at the principal focus, highly diminished (point sized), virtual and erect. Between infinity and optical centre, 1. 2. In this article, we will learn about image formation by concave and convex lenses. Concave lens point object at infinity, image at focus. It is virtual–erect and diminished (fig.) At infinity 2. A point object lying on the principal axis: Rays come parallel to the principal axis … Parallel rays from infinity Fig. Formation of image by a concave lens when the object is placed at infinity When an object is placed at infinity, the two rays AO and BD running parallel to the principal axis get refracted at point O and D respectively and get diverged along the directions OX and DY respectively. Case 4: Object at distance more than Focal Length and less than twice is Focal Length Real object AB has its image A’B’ formed beyond distance 2f. Image of foot is formed at the focus. First, we draw a ray parallel to principal axis. The image is formed at focus F2. Why concave lens is called diverging lens? Convex lens : object at focus, image at infinity. At 2F 4. (Fig.) Case 2:When object is placed at 2F In this case image will form at 2F, also image will be real , inverted, the same as the size of the object. A big size object with its foot on the principal axis: Parallel rays come inclined to the principal axis. Images through lenses as real, virtual, erect or magnified. Fig. A concave lens is thin in the middle and thick at the edges. Beyond 2F 3. When an object is placed at infinity, the two rays AO and BD running parallel to the principal axis get refracted at point O and D respectively and get diverged along the directions OX and DY respectively. Case 2: Object at a Finite Distance Real object AB has its image A’B’ formed between second principal focus F2 optical centre C. The image is virtual–erect and diminished. Table of Summary of Image Formed by a Concave Lens, Differences between a Convex Lens and a Concave Lens. Convex lens : object at distance 2f, image at distance 2f. Image formation by a concave mirror for different positions of the object is shown below in the table Concave mirrors are used as shaving mirrors, reflectors in car headlights, hand torch and table lamps. (a) Between the principal focus and the centre of curvature Convex lens : object beyond 2f, image between f and 2f. Hence, the image A’B’ formed in this case is a virtual image which is formed at the same side of the lens, between the optical centre and focus. Case 2: Object at distance more than twice the Focal Length Real object AB has its image A’B’ formed between distance f and 2f. OX and CY are diverging in nature, so these rays appear to intersect each other at point A’ on the left side of the lens on producing back. At the focus F 6. Fig. Also the image formed is diminished and erect. Between the focus F and optical centre C. 1. Large concave mirrors are used in field of solar energy to focus sun rays on objects to be heated. Questions Question 3 Page 168 - Name a mirror that can give an erect and enlarged image of an object View Answer NCERT Question 2 - The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Between F and 2F 5. We cannot get such image using a concave lens because the concave lens always produces the diminished image. Object at Infinity. The image is real inverted and enlarged (bigger in size than the object). The figure shows the virtual image formed by the convex lens and real image formed by a concave lens. Test Your Understanding and Answer These Questions: Rules for Obtaining Images by Spherical Lenses. The image is imaginary inverted (refracted rays to downward) and must have very large size. It is real inverted and diminished (smaller in size than the object). Concave lens : big size object at infinity image at focus. Fig. A big size object with its foot on the principal axis: Parallel rays come inclined to the principal axis. Ray diagram for concave lens. As a convex lens forms different types of images depending on the position of object, similarly a concave lens also forms different types of images when the object is placed at, 1. We draw another ray which passes through… It is virtual and point sized (fig.). Convex lenses are also known as converging lenses since the rays converge after falling on the convex lens while the concave lenses are known as diverging lenses as the rays diverge after falling on the concave lens. Case 3: Object at distance twice the Focal Lengths Real object AB has its image A’B’ formed at distance 2f. Give differences between a concave lens and convex lens. Convex lens point object at infinity, image at focus. Explain formation of different types of images by a concave lens. While the other ray of light AC goes straight through the optical centre C of the concave lens without any deviation along the direction CY. Formation of image by a concave lens when the object is placed at infinity. A concave lens is called diverging lens because of its ability to diverge a parallel beam of light. A convex lens is thick in the middle and thin at the edges. Describe with the help of a ray diagram the position, size and nature of the image formed by a concave lens when the object is placed at infinity. It is real and point sized. OX and DY appears to intersect each other at the principal focus of the concave lens after extending back by dotted lines. We will now discuss the formation of different types of images by a convex lens when the object is placed 1. The image is formed at focus F2. Convex lens : object at distance between f and 2f, image beyond 2f. Case 3:When object is placed between F and 2F The image is real, inverted and has same size as the object. The image is formed at the second principal focus F2. For a Concave lens,There are only 2 casesThey areObject is Placed at InfinityObject is Placed between Infinity and Optical CenterCase 1 - Object is Placed at infinityIn this Case, Object is kept far away from mirror (almost at infinite distance)So, we draw rays parallel to principal axisSince ray pa Fig. Fig. Image formed by a convex lens when the object is placed at infinity So this is a convex lens. When an object AB is placed between infinity and optical centre of a concave lens, a ray of light AO which is parallel to the principal axis diverges along the direction OX after refraction and appears to come from the principal focus F along the direction OF. Yes, an enlarged image is formed. Case 1: Object at Infinity A point object lying on the principal axis: Rays come parallel to the principal axis and after refraction from the lens, actually meet at the second principal focus F2. The image is real inverted and diminished (smaller in size than the object) Fig. As it is clear from the figure (given below) that both the refracted rays i.e. Here, Object AB is at 2F 1. Image is formed at the second principal focus F2. At infinity 2. Image formation by convex mirrors Case 6: Object between Focus and Optical Centre Real object AB has its image A’B’ formed in front of the lens. 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