Activity 9.12

Activity . Take a convex lens. Find its approximate focal length in a way described in Activity . . 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. 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. 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 2F , F , F and 2F , respectively. Place a burning candle, far beyond 2F to the left. Obtain a clear sharp image on a screen on the opposite side of the lens. Note down the nature, position and relative size of the image. Repeat this Activity by placing object just behind 2F , between F and 2F at F , between F 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 . . Let us now do an Activity to study the nature, position and relative size of the image formed by a concave lens. Table . 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 F Highly diminished, point-sized Beyond 2F Between F and 2F Diminished At 2F At 2F Same size Between F and 2F Beyond 2F Enlarged At focus F At infinity Infinitely large or highly enlarged Between focus F On the same side Enlarged Virtual and erect and of the lens as the optical centre O object The summary of the above Activity is given in Table . below.