We have studied the converging and diverging nature of spherical lenses. Now let us look at the activity that explains the image formed by the concave and convex mirrors.
  • Take a convex lens.
  • Draw five parallel straight lines on a long table with chalk so that the distance between the successive lines equals the focal length of the lens.
  • Place the lens on a lens stand.
  • Place it so that the optical centre of the lens is just over the line on the central line.
  • The two lines on either side of the lens correspond to \(F\) and \(2F\) of the lens, respectively.
  • Mark them with the appropriate letters, such as \(2\)F1, F1, F2, and 2F2. Place a burning candle far to the left of \(2\)F1.
  • On a screen on the other side of the lens, get a clear, sharp image. Make a note of the image's nature, location, and relative size.
  • Place the object behind \(2\)F1, between F1F1 and \(2\)F1 at F1, and between F1 and \(O\) to repeat the activity.
  • Make a list of your observations and tabulate them.
Image formation by convex lenses:
Object at infinity
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Beyond \(2\)F1
At \(2\)F1
Between F1 and \(2\)F1
At focus F1
Between F1 and \(O\)
The nature, position and relative size of the image formed by a convex lens for various object positions are summarised in the table below.