(vii) Draw a line CA', backwards, so that it meets the line from D parallel to principal axis at 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. 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]. All distances are measured from the pole of the mirror. I. 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. 2020 Zigya Technology Labs Pvt. Image size, h' = ? Converging lens means a convex lens. Notify me of follow-up comments by email. It is denoted by the letter ‘v’. 232, Block C-3, Janakpuri, New Delhi, We are given a convex mirror. List the sign conventions for reflection of light by spherical mirrors. At what distance from the mirror should a screen be placed so that a sharp focussed image can be obtained? 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 draw the ray diagram as follows:(i) Draw the principal axis (a horizontal line). An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. 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 … (viii) Draw a line AB, perpendicular (downwards) from A to meet the principal axis at B. (ii) Draw a convex lens, keeping principal centre (C) on the principal axis. (vi) The distances (heights) measured upwards (i.e. Sign conventions for reflection of light by spherical mirror are: 1. In this convention, the pole (P) of the mirror is taken as the origin. 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. 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. 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. The object is always placed to the left of the mirror. © All distances are measured from the pole of the mirror. (iv) All the distances measured to the right of the origin (along +ve x-axis) are taken as positive. Objects are always placed to the left of the mirror i.e. (ix) Now AB', represents the real, but inverted image of the object AB. In this convention, the pole (P) of the mirror is taken as the origin. Now, we draw the ray diagram as follows:(i) Draw a horizontal line to represent the principal axis of the convex lens. The Mirror formula can be written as : where the symbols have their usual meaning. Ltd. Download books and chapters from book store. III. light must fall on the mirror from left to right. Draw the ray diagram. Distances measured along the direction of the incident ray are positive. light must fall on the mirror from left to right. : Sign conventions for spherical mirrors I. The principal axis of the mirror is taken as the x-axis (X’X) of the coordinate system. Let us first know about the terms used in the mirror formula of spherical mirrors. Learn how your comment data is processed. Sign Convention for Spherical Mirrors (Concave and Convex Mirrors) Distances are to be measured from the pole (vertex) of the mirror marked by point V in the figure. Therefore, on this scale 5 cm high object, object distance of 25 cm and focal length of 10 cm can be represented by 1 cm high, 5 cm and 2 cm lines respectively. Concepts NCERT Questions; (v) Draw a line AD, parallel to principal axis. (viii) Draw AB', perpendicular to the principal axis from A'. Delhi - 110058. Objects are always placed to the left of the mirror i.e. Sign convention for Spherical Mirrors. Heights measured perpendicular to and above the principal axis (along positive Y-axis) are taken as positive. 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. Sign is taken as – (negative) from pole of a spherical mirror towards object along the principal axis. (iv) Draw an arrow AB of height 1 cm on the left side of lens at a distance of 5 cm from the lens. IV. The new Cartesian sign convention is used for measuring the various distances in the ray-diagrams of spherical mirrors. https://www.zigya.com/share/U0NFTjEwMTEyMzgy. Sign convention. (xi) Thus the final position, nature and size of the image A'B' are: (a) Position of image A'B' = 3.3 cm × 5 = 16.5 cm from the lens on opposite side. 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. 32 illustrates all the points of the new cartesian sign convention stated above. Magnification, m = -vu= h'h Therefore, Image size, h' = -vhu = -8.6 × 5-20 = 2.15 ≃ 2.2 cm. (ii) The object is always placed to the left of the mirror i.e. II. This site uses Akismet to reduce spam. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. (iii) Focal length (f) : The distance of the principal focus (F) from the pole (P) of the spherical mirror is called the focal length. 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. 2. Draw a diagram and apply these conventions in the determination of focal length of a spherical mirror which forms a three times magnified real image of an object placed 16 cm in front of it. (ii) Image Distance (v) : The distance of the image from the pole ‘P’ of the spherical mirror is called the image distance. II. (b) Nature of image A’B’: Real and inverted. above the x-axis) and perpendicular to the principal axis of the mirror are taken as positive. (vii) Let the two lines starting from A meet at A'. 10th Physics | Light | Sign Convention for Reflection by Spherical Mirrors and Mirror Formula. (iii) Mark two foci F and F' on two sides of the lens, each at a distance of 2 cm from the lens. (c) Height of image A'B': 0.7 × 5 = 3.5 cm, i.e., image is smaller than the object. (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. As the distances given in the question are large, so we choose a scale of 1: 5, i.e., 1 cm represents 5 cm. Drawing the ray diagram: Using a scale of 1: 5, we get v = - 2 cm, f = - 3 cm. The image is real, inverted and enlarged in size. Find the position of the image, its nature and size. Required fields are marked *, You may use these HTML tags and attributes:
. Your email address will not be published. (vi) Draw a line from A to C (centre of the lens), which goes straight without deviation. below the x-axis) and perpendicular to the principal axis of the mirror are taken as negative. The distance measured opposite the direction of … This sign convention is known as New Cartesian Sign Convention. We are given a concave mirror. 3. Last updated at April 23, 2020 by Teachoo. The principal axis of the mirror is taken as the x-axis (X'X) of the coordinate system. All the distances parallel to the principal axis are always measured from the pole of the spherical mirror. Here, we have Object size, h = + 5 cm Object distance, u = -20 cmRadius of curvature, R = + 3.0 cm [R is +ve for a convex mirror]∴ Focal length , f = R2 = +15 cm From mirror formula, 1v = 1f-1u we have, 1v= 1+15-1-20 = 4+360 = 760 Image distance, v = 607≃ 8.6 cm. Ans. should be placed at a distance of 54 cm on the object side of the mirror to obtain a sharp image. V. Heights measured perpendicular to and below the principal axis (along negative Y-axis) are taken as negative. Magnification, m = −3 (real image is inverted always). Your email address will not be published. The following fig. Download the PDF Question Papers Free for off line practice and view the Solutions online. It is denoted by the letter ‘u’.
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