Image Formation in Concave and Convex Lens**
THE PHYSICS CAFE
CHAPTER TEN - LIGHT - REFLECTION
AND REFRACTION
1.18 Image Formation in
Concave and Convex Lens**
Rules for Image Formation
in both Concave and Convex Lens:
- Always
place the object left side of lens.
- Take
two light rays from the head of object. One parallel to principal axis and
second incident at optical centre.
- Incident
light ray parallel to principal axis will always pass through focus.
- Incident
light ray falling at optical centre will always refract in the direction
of incident light ray (without bending).
- Image
will be formed at the point where both the refracted light ray meets. The
distance of this point from optical centre is called Position of
image
- If
both refracted light ray meets actually then the image formed will be Real image and if both refracted light ray
don’t meet actually, then extend them backside then the image will be
formed at the point where extended rays meet and this type of image is
called Virtual image.
- Hint:
The arrow head represents the head of the object/image and foot will
always lie on principal axis.
- Size of the image
is told as compared to object’s size, like image formed is point sized,
small sized, same sized, large sized, very large sized as compared to
object’s size.
Hint:
Real Image: Real image formed where refracted light ray actually
meets
Virtual Image: Virtual image formed where backside extended
refracted light rays meets.
To
see image formation video lecture click here…
1.19 Checking of Position, Nature and Size of Image
We have six positions to place the object in front of convex lens.
If object
is placed at infinity, light rays come parallel to principal axis and after refraction
by lens meets at focus, thus image will be formed at focus. Now check in your
notebook if object is placed at infinity and the image is formed at focus, then
it is correct otherwise find mistake and re-draw.
Hint: Dimensions must be proper for correct result.
From the above table we can see as we move object one position towards the Lens from infinity to between infinity and 2F¹, the image moves one position away from the Lens from focus (1F²) to between 1F² and 2F² and so on
We have six positions to place the object in front of concave lens
Hint: Concave lens always forms small sized, erect and virtual images.
Uses of
Concave and Convex Lens in Daily Life*
- In
many optical instruments
- Eye
defection correction (vision lens in specs)
- As
a magnifying glass etc
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