|
|
THIN LENS FORMULA
|
|||
|
FOR
CONCAVE LENS
|
|||
Consider
an object  placed
in front of a concave lens of focal length " f " on the
principle axis of the lens. Concave lens forms a virtual and erect image
 at a distance
of " q " from the optical centre of the lens as shown in
the diagram below. |
|||
 |
|||
| For
latest information , free computer courses and high impact notes visit :
www.citycollegiate.com Consider similar triangles 
and  |
|||
 |
|||
Similarly
in similar triangles  and
 |
|||
 |
|||
|
.............
 |
|||
| Comparing equation (1) and (2) | |||
 |
|||
|
p
(f - q) = fq
|
|||
|
pf
- pq = fq
|
|||
| Dividing both sides by "pqf" | |||
 1/q - 1/f = 1/p |
|||
| For
a concave lens: f = negative, q = negative , i.e. f = -f and q = -q Thus, |
|||
|
-1/q
+ 1/f = 1/p
|
|||
 |
|||
| For latest information , free computer courses and high impact notes visit : www.citycollegiate.com | |||