Theory:

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 $$2$$${F}_{1}$, ${F}_{1}$, ${F}_{2}$, and 2${F}_{2}$. Place a burning candle far to the left of $$2$$${F}_{1}$.
• 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 $$2$$${F}_{1}$, between F1${F}_{1}$ and $$2$$${F}_{1}$ at ${F}_{1}$, and between ${F}_{1}$ and $$O$$ to repeat the activity.
• Make a list of your observations and tabulate them.
Image formation by convex lenses:

Object at infinity

Beyond $$2$$${F}_{1}$

At $$2$$${F}_{1}$

Between ${F}_{1}$ and $$2$$${F}_{1}$

At focus ${F}_{1}$

Between ${F}_{1}$ 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.