An image is formed when two or more rays meet at a point. In actual sense, millions of rays meet for an image to be formed. When rays meet and forms an image, the image formed is refered to as a real image.
When determining images formed by a lens, we consider a ray from a point object. Appoint object is a tiny point from the object.
Image formation works just the way eyes work. For you to see any object, rays of light must fall onto the object and then be reflected into your eyes, so that your eyes can form the image about the object on the retina.
The rays must converge after passing through the eye lens for the image to be formed on the retina. Similarly, thin convex lenses converges the rays that fall on it to form an image of the object. The rays of light falls on the object before they are reflected towards the lens.
There are three important rays we use to show image formation by lenses.
These rays are:
- A ray reflected from an object that moves parallel to the principal axis and is refracted such that it passes through the principal focus or appears to emerge from the principal focus after refraction.
For a diverging lens, the ray will only appear to be coming from the principal focus as shown
- A ray that passes from the object and towards the optical center of the lens that passes through the lens undeviated.
- A ray that passes from the object and passes through the principal focus and that will move parallel to the principal axis after it it is being refracted.
Meeting of any two rays out the three mentioned will be sufficient to represent an image on a diagram.
The diagram below shows the three rays meeting at a point to form an image of the object
We usually use an upright arrow to represent an object.
for a concave lens, the image formation is imagined by the eye as illustrated below.
Conclusion
- image formation needs at least two rays to meet.
- Three rays are common is identifying an image.
- Image formation by concave lenses is very different from that of concave lens.
- Next lesson we will discuss image formation by concave lens.
Related lessons
- Terms used in thin lenses
- Introduction to thin lenses
- Focal length by non-parallax method
Estimating focal length
focusing a distance object
The lens formula
Linear magnification
Ray diagrams
Image formation by thin lenses
Introduction to thin lenses
Finding focal length by displacement - Physics