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NCERT Solutions for Class 10 Chapter 10 Image 7 The image is located at a distance of 6 cm from the mirror on the other side of the mirror. The positive and a value of less than 1 of magnification indicates that the image formed is virtual and erect and diminished. 13. The magnification produced by a plane mirror is +1. What does this mean? Answer- The positive sign means an image formed by a plane mirror is virtual and erect. Since the magnification is 1 it means that the size of the image is equal to the size of the object. 14. An object 5 cm is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position, nature and size of the image. Answer- Object distance (u) = – 20 cm Object height (h) = 5 cm Radius of curvature (R) = 30 cm Radius of curvature = 2 × Focal length R = 2f f = 15 cm According to the mirror formula, NCERT Solutions for Class 10 Chapter 10 Image 8 The positive value of image height indicates that the image formed is erect. Hence, the image formed is erect, virtual, and smaller in size. 15. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed so that a sharply focused image can be obtained? Find the size and nature of the image. Answer- Object distance (u) = – 27 cm Object height (h) = 7 cm Focal length (f) = – 18 cm According to the mirror formula, NCERT Solutions for Class 10 Chapter 10 Image 9 The negative value of image height indicates that the image formed is inverted. 16. Find the focal length of a lens of power -2.0 D. What type of lens is this? Answer- Power of lens (P) = 1/f P = -2D f = -1/2 = -0.5 m A concave lens has a negative focal length. Therefore, it is a concave lens. 17. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging? Answer- Power of lens (P) = 1/f P = 1.5D f = 1/1.5 = 10/15 = 0.66 m A convex lens has a positive focal length. Therefore, it is a convex lens or a converging lens.