A virtual and erect image of height 2.2 cm is formed behind the mirror (because v is positive) at a distance of 8.6 cm from the mirror. All the distances parallel to the principal axis are always measured from the pole of the spherical mirror. Converging lens means a convex lens. Let us first know about the terms used in the mirror formula of spherical mirrors. (ix) Now AB', represents the real, but inverted image of the object AB. The new Cartesian sign convention is used for measuring the various distances in the ray-diagrams of spherical mirrors. (ix) The AB is position of object. (iii) Mark two foci F and F' on two sides of the lens, each at a distance of 2 cm from the lens. (iv) Draw an arrow AB of height 1 cm on the left side of lens at a distance of 5 cm from the lens. Sign Convention for Reflection by Spherical Mirrors The new Cartesian sign convention is used for measuring the various distances in the ray-diagrams of spherical mirrors. Image size, h' = ? II. (ii) Draw a convex lens, keeping principal centre (C) on the principal axis. : Sign conventions for spherical mirrors I. This site uses Akismet to reduce spam. The sign convention mentioned below helps us in it We can see the sign convention in both mirrors Some points to note ... Chapter 10 Class 10 - Light - Reflection and Refraction. A virtual and erect image of height 2.2 cm is formed behind the mirror (because v is positive) at a distance of 8.6 cm from the mirror. 2. It is denoted by the letter ‘f ‘. Concepts NCERT Questions; In this convention, the pole (P) of the mirror is taken as the origin. Heights measured perpendicular to and above the principal axis (along positive Y-axis) are taken as positive. the light (incident rays) from the object falls on the mirror from the left hand side. According to the new Cartesian sign convention (figure 1) : (i) The pole ‘P’ of the mirror is taken as the origin and the principal axis of the mirror is taken as the x-axis of the coordinate system. In this convention, the pole (P) of the mirror is taken as the origin. Sign is taken as – (negative) from pole of a spherical mirror towards object along the principal axis. (viii) Draw AB', perpendicular to the principal axis from A'. The relationship between the image distance (v), object distance (u) and focal length (f ) of a spherical mirror is known as the mirror formula. Find the size and the nature of the image. (vi) Draw a line from A to C (centre of the lens), which goes straight without deviation. I. Find the position of the image, its nature and size. Download the PDF Question Papers Free for off line practice and view the Solutions online. Objects are always placed to the left of the mirror i.e. 10th Physics | Light | Sign Convention for Reflection by Spherical Mirrors and Mirror Formula. The following fig. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. List the sign conventions for reflection of light by spherical mirrors. (ii) Image Distance (v) : The distance of the image from the pole ‘P’ of the spherical mirror is called the image distance. All distances are measured from the pole of the mirror. (v) Draw a line AD, parallel to principal axis. (c) Height of image A'B': 0.7 × 5 = 3.5 cm, i.e., image is smaller than the object. Sign convention for reflection by spherical mirrors Reflection of light by spherical mirrors follow a set of sign conventions called the New Cartesian Sign Convention. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. We draw the ray diagram as follows:(i) Draw the principal axis (a horizontal line). 32 illustrates all the points of the new cartesian sign convention stated above. Last updated at April 23, 2020 by Teachoo. Distances measured along the direction of the incident ray are positive. Ltd. Download books and chapters from book store. (x) Then, measure CB' and A'B'. The distance measured opposite the direction of … Focal length, f = - 15 cm [f is - ve for a concave lens]Image distance, v = - 10 cm [Concave lens forms virtual image on same side as the object, so v is - ve]As, Object distance, u = -30 cm. Ans. Sign conventions for reflection of light by spherical mirror are: 1. (b) Nature of image A’B’: Real and inverted. 3. 2020 Zigya Technology Labs Pvt. As the distances given in the question are large, so we choose a scale of 1: 5, i.e., 1 cm represents 5 cm. (ii) The object is always placed to the left of the mirror i.e. light must fall on the mirror from left to right. Magnification, m = −3 (real image is inverted always). Draw the ray diagram. (iii) Mark points F and B on the left side of lens at a distance of 3 cm and 2 cm respectively. (viii) Draw a line AB, perpendicular (downwards) from A to meet the principal axis at B. above the x-axis) and perpendicular to the principal axis of the mirror are taken as positive. Now, using the mirror formula, 1u+1v = 1f∴ 1v = 1f-1u ⇒ = 1-18-1-27 = -3+254 = -154i.e., v = -54 cm The screen should be placed at a distance of 54 cm on the object side of the mirror to obtain a sharp image. Sign convention. Your email address will not be published. Notify me of follow-up comments by email. 232, Block C-3, Janakpuri, New Delhi, (i) Object distance (u) : The distance of the object from the pole ‘P’ of the spherical mirror is called the object distance. https://www.zigya.com/share/U0NFTjEwMTEyMzgy. It will be found to be equal to 6 cm.Thus, object is placed at a distance of 6 cm × 5 = 30 cm from the lens. III. (v) Draw a line AD parallel to principal axis and then, allow it to pass straight through the focus (F') on the right side of the lens. The principal axis of the mirror is taken as the x-axis (X'X) of the coordinate system. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained? (iii) All the distances parallel to the principal axis of the spherical mirrors are measured from the pole ‘P’ of the mirror. It is found that CB' = 3.3 cm and A'B' = 0.7 cm. (vii) Let the two lines starting from A meet at A'. Magnification, m = h'h = -vu ∴ Image size, h' = -vhu =-(-54)×(+7)(-27)= -14 cm The image is real, inverted and enlarged in size. An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. We are given a convex mirror. IV. Distances along the direction of the incident ray (along positive X - axis) are taken as positive, while distances along the direction of the reflected ray (along negative X-axis) are taken as negative. Delhi - 110058. How far is the object placed from the lens? III. (ii) Centre line is shown by DE. (iv) All the distances measured to the right of the origin (along +ve x-axis) are taken as positive. (vii) the distances (heights) measured downwards (i.e. The image is real, inverted and enlarged in size. The object is always placed to the left of the mirror. Drawing the ray diagram: Using a scale of 1: 5, we get v = - 2 cm, f = - 3 cm. Sign Convention for Spherical Mirror: Cartesian Sign Convention: In the case of spherical mirror all signs are taken from Pole of the spherical mirror, which is often called origin or origin point. light must fall on the mirror from left to right. II. 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