This can be proved as follows. New Cartesian Sign Convention for spherical lenses: (i) All the distances are measured from the optical centre of the lens. These rays, after refraction from the lens, are converging to a point on the principal axis. It is given by, If medium 1 is vacuum or air, then the refractive index of medium 2 is considered with respect to vacuum. ll A measurements are taken from the optical centre of the lens which lies on the origin of x-y axis. It is represented by the letter f. There is a relationship between the radius of curvature R, and focal length f, of a spherical mirror and is given by R=2f which means that that the principal focus of a spherical mirror lies midway between the pole and centre of curvature. A concave lens bulges inward and is thinner in the middle and thicker at the edges. For understanding about principle focus and focus length of a spherical mirror first consider the figure given below. When the distances are measured opposite to the direction of the incident light, they are considered to be negative. Secondly consider the case for concave lens, The ray diagrams for the image formation in a convex lens for a few positions of the object are summarized below in the table, The ray diagrams for the image formation in a concave lens for a few positions of the object are summarized below in the table. ... Spherical lenses formed by binding two spherical surfaces bulging outward are known as convex lenses while the spherical lenses formed by binding two spherical surfaces such that they are curved inward are known as concave lenses. Now on entering the glass medium this ray bends towards the normal NN’ that is light ray, After getting refracted this ray now travels through the glass slab and at point, Emergent ray is parallel to incident ray because the extent of bending of the ray of light at the opposite parallel faces which are. The magnification produced by a lens is defined as the ratio of the height of the image and the height of the object. All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along - x-axis) are taken as negative. This implies that the light from the object falls on the mirror from the left-hand side. Given below are the links of some of the reference books for class 10 Science. However, it lies behind the mirror in case of a convex mirror as shown above in the figure 2. The distances measured upward and perpendicular to the principle axis are taken as positive. The refractive index of medium 1 with respect to medium 2 is represented as n12. If i is the angle of incidence and r is the angle of refraction then According to the convention, the focal length of a convex lens is positive and that ofa concave lens is negative. Hence incident and emergent rays are parallel. The distances measured against the direction of incident light are taken as negative. If we now observe the reflected rays we see that they are all intersecting at a point F on the principal axis of the mirror. A ray of light through the optical centre of a lens passes without suffering any deviation. Light rays basically consist of electromagnetic waves which do not require any material medium 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. This emergent ray is parallel to the incident ray. The new sign convention is known as New Cartesian Sign Convention. A ray of light parallel to the principle axis of a convex mirror appears to be coming from its focus after reflection from the mirror. This point on the principal axis is called the principal focus of the concave lens. and when this reflected light reaches our eyes we are able to see such non luminous objects. A convex lens bulges outward and is thick at the center and thinner at the edges. A concave lens will always give a virtual, erect and diminished image, irrespective of the position of the object. (like solid, liquid or gas) for their propagation. which are not luminous objects and still we are able to see them This is called the, If c is the speed of light in the air and v is the speed of light in any medium then refractive index n. In the figure given above ABCD is a rectangular glass slab of thickness AD=BC=t. Radius of curvature (ROC) has specific meaning and sign convention in optical design.A spherical lens or mirror surface has a center of curvature located either along or decentered from the system local optical axis.The vertex of the lens surface is located on the local optical axis. It is usually represented by the letter O. Sign convention for lens: Sign convention for lens is similar to that of spherical mirror. (a) Images formed by mirrors are always virtual and erect. Ray diagram helps us to study the nature, position and relative size of the image formed by lenses. To understand the refraction of light through a glass slab consider the figure given below which shows the refraction of light through a rectangular glass slab. Sign Convention for Spherical Lenses. All right reserved. These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces. The distances measured against the direction of incident light are taken as negative. Commonly used terms about Spherical mirrors :-. Such lenses diverge light rays as shown in Figure 1(b). For drawing ray diagrams we first consider how light rays falling on both concave and convex lens in three different ways get refracted. Class 6. Center of curvature: - The reflecting surface of a spherical mirror forms a part of a sphere. The refraction of light takes place on going from one medium to another because the speed of light is different in two media. There are objects like table , chair etc. The SI unit of power of a lens is ‘diopter’. This ray refracts in the glass slab and goes along QR as refracted ray (as shown in the figure) and becomes incident on face DC at point R from inside the slab. It includes the basics of lens diagrams, the refractive index, prisms, spherical lenses, cylindrical lenses, lens form, transposition, base curves, and vertex distance. All material given in this website is a property of and is for your personal and non-commercial use only, Gravitation NCERT Solutions Class11 physics, Trigonometry Formulas for class 11 (PDF download), Newton�s law Interesting conceptual questions, Difference between resistance and resistivity, Sign convention for reflection by spherical mirrors, Refraction through a rectangular glass slab, Reflection and Refraction Formative Assignment, Reflection and Refraction Unsolved test paper, Reflection and Refraction Short questions, Reflection and Refraction 3 Mark questions, Reflection and Refraction 5 Mark questions, Practice questions for Reflection of light(download), Oswaal CBSE Question Bank Class 10 Hindi B, English Communication Science, Social Science & Maths (Set of 5 Books), Combo Pack: Science for Class 10 () This post covers my notes from Chapters 12-14 in the System for Opthalmic Dispensing. These rays, after refraction from the lens, are appearing to diverge from a point on the principal axis. (i) The object is always placed to the left of the mirror. Sign convention for spherical lenses; ... Sign convention: Sign convention. Following sign convention is used for measuring various distances during the formation of images by lenses: All distances on the principal axis are measured from the optical center.

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