There are only two possibilities of position of object in the case of a concave lens: In each of these cases, image is highly reduced in size, is erect and virtual and formed in front of the lens, i.e. on the same size as object. A highly diminished point sized, virtual and erect image is formed when object is at infinity by a concave lens at principal focus F1. Fig: Object at Infinity This figure shows a concave lens. Light rays are parallel to the principal axis which shows that they are coming from infinity. After passing through the lens, light rays diverge from the lens and appear to be coming from the focus. That is why image is formed on the focus of the lens. Properties of Image: Image is point sized, highly diminished, virtual and erect. A diminished, virtual and erect image is formed between principal focus F1 and optical centre, O; when object is placed between optical centre and infinity of a concave lens. Fig: Object between Infinity and O This figure shows a concave lens. One of the rays of light is parallel to the principal axis and another ray of light is passing through the optical centre of lens. When both the emergent rays are drawn backwards they appear to be intersecting somewhere between F and O. So, image if formed between F and O. Properties of Image: Image is diminished, virtual and erect. Sign convention for lens is similar to that of spherical mirror. Signs are taken left of the optical centre as negative, right of the optical centre as positive, above of the principal axis as positive and below of the principal axis as negative. Fig: Sign Convention The new sign convention is known as New Cartesian Sign Convention. In this sign is taken negative towards left and taken as positive towards right at X-axis from origin. The sign is taken as positive (+) above the origin point at Y-axis; and below the origin point as negative (-) at Y-axis. Copyright © excellup 2014 Spherical lenses are lenses formed by connecting two spherical transparent surfaces. In general, there are two types of spherical lenses. So, lenses formed by binding two spherical surfaces bulging outward are known as convex lenses, while the lenses formed by binding two spherical surfaces such that they are curved inward are known as concave lenses. This is one of the basic difference between concave and convex lenses. Convex lenses are also known as converging lenses since the rays converge after falling on the convex lens. The concave lenses are known as diverging lenses, as the rays diverge after falling on the concave lens. In this article, we will learn about image formation by concave and convex lenses.
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out of 0 arewrong out of 0 are correct out of 0 are Unattempted View Quiz Answers and AnalysisAs 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. At infinity 1. 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. These diverged rays i.e. OX and DY appears to intersect each other at the principal focus of the concave lens after extending back by dotted lines. 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. Why concave lens is called diverging lens? A concave lens is called diverging lens because of its ability to diverge a parallel beam of light. 2. When the object is placed between infinity and optical centre 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. 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. As it is clear from the figure (given below) that both the refracted rays i.e. 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. 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. Also the image formed is diminished and erect. Table of Summary of Image Formed by a Concave Lens
Differences between a Convex Lens and a Concave Lens
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When the image is at focus of a concave lens?
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