Light - Reflection and - 19 PDF

9.3.4 Image Formation by Lenses Lenses form images by refracting light. How do lenses form images? What is their nature? Let us study this for a convex lens first. Activity 9.12 n Take a convex...

9.3.4 Image Formation by Lenses Lenses form images by refracting light. How do lenses form images? What is their nature? Let us study this for a convex lens first. Activity 9.12 n Take a convex lens. Find its approximate focal length in a way described in Activity 9.11. n Draw five parallel straight lines, using chalk, on a long Table such that the distance between the successive lines is equal to the focal length of the lens. n Place the lens on a lens stand. Place it on the central line such that the optical centre of the lens lies just over the line. n The two lines on either side of the lens correspond to F and 2F of the lens respectively. Mark them with appropriate letters such as 2F1, F1, F2 and 2F2, respectively. n Place a burning candle, far beyond 2F1 to the left. Obtain a clear sharp image on a screen on the opposite side of the lens. n Note down the nature, position and relative size of the image. n Repeat this Activity by placing object just behind 2F1, between F1 and 2F1 at F1, between F1 and O. Note down and tabulate your observations. The nature, position and relative size of the image formed by convex lens for various positions of the object is summarised in Table 9.4. Table 9.4 Nature, position and relative size of the image formed by a convex lens for various positions of the object Position of the Position of Relative size of Nature of object the image the image the image At infinity At focus F2 Highly diminished, Real and inverted point-sized Beyond 2F1 Between F2 and 2F2 Diminished Real and inverted At 2F1 At 2F2 Same size Real and inverted Between F1 and 2F1 Beyond 2F2 Enlarged Real and inverted At focus F1 At infinity Infinitely large or Real and inverted highly enlarged Between focus F1 On the same side Enlarged Virtual and erect and of the lens as the optical centre O object Let us now do an Activity to study the nature, position and relative size of the image formed by a concave lens. 152 Science 2024-25