directly with our eye?
Measure the distance of the image from the v-stand of lens and also
measure the distance between the candle and stand of lens.
Record the values in a table 1.
Object distance (u)
Image distance (v)
Focal length (f)
0
0
0
Table 1
Now place the candle at a distance
of 60 cm from the lens, such that the<
flame of the candle lies on the principal
axis of the lens. Try to get an image of
the candle flame on the other side on a
screen. Adjust the screen till you get a
clear image. Measure the image
distance (v) from lens and record the values of ‘u’ and ‘v’ in table 1. Repeat
this for various object distances like 50 cm, 40 cm, 30 cm, etc. Measure
image distances in all the cases and note them in table 1.
Could you get an image on the screen for every object distance?
Why don’t you get an image for certain object distances?
Can you find the minimum limiting object distance for obtaining a
real image?
What do you call this minimum limiting object distance for real images?
When you do not get an image on the screen, try to see the image with
your eye directly from the place of the screen.
Could you see the image?
What type of image do you see?
You will see a magnified image on the same side where we kept the
object. This is a virtual image of the object which we cannot capture on
the screen.
Can you find the image distance of this virtual image?
In table-1, you got different values of ‘v’ for various position of candle
(u).
Could you find focal length of the lens from the values recorded in
table-1?
Can we establish a relation between ‘u’, ‘v’ and ‘f’?
Let us find out.
Consider an object OOI placed on the principal axis in front of a convex
lens as shown in fig.-(19). Let III be the real image formed by the lens on
the other side of it. Observe the fig.-(19).