Light – Reflection and-11 PDF Physics Past Paper

Example 9.1 A convex mirror used for rear-view on an automobile has a radius of curvature of 3.00 m. If a bus is located at 5.00 m from this mirror, find the position, nature and size of the image. Solution Radius of curvature, R = + 3.00 m; Object-distance, u...

Example 9.1 A convex mirror used for rear-view on an automobile has a radius of curvature of 3.00 m. If a bus is located at 5.00 m from this mirror, find the position, nature and size of the image. Solution Radius of curvature, R = + 3.00 m; Object-distance, u = – 5.00 m; Image-distance, v =? Height of the image, h ′ = ? 3.00 m Focal length, f = R/2 = + = + 1.50 m (as the principal focus of 2 a convex mirror is behind the mirror) 1 1 1 Since + = v u f 1 1 1 1 1 1 1 or, = − =+ – = + v f u 1.50 ( −5.00) 1.50 5.00 5.00 + 1.50 = 7.50 +7.50 v= = + 1.15 m 6.50 The image is 1.15 m at the back of the mirror. h' v 1.15 m Magnification, m = = − = – h u −5.00 m = + 0.23 The image is virtual, erect and smaller in size by a factor of 0.23. Example 9.2 An object, 4.0 cm in size, is placed at 25.0 cm in front of a concave mirror of focal length 15.0 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Find the nature and the size of the image. Solution Object-size, h = + 4.0 cm; Object-distance, u = – 25.0 cm; Focal length, f = –15.0 cm; Image-distance, v = ? Image-size, h ′ = ? From Eq. (10.1): 1 1 1 + = v u f 1 1 1 1 1 1 1 or, = − = − = − + v f u −15.0 −25.0 15.0 25.0 144 Science 2024-25