1. Image Formation
Preliminary Physics

2. Reflection of Light and Image Formation
Light always follows the law of reflection, whether the reflection occurs off a curved surface or off a flat surface. The task of determining the direction in which an incident light ray would reflect involves determining the normal to the surface at the point of incidence.

3. Concave Mirror
For a concave mirror, the normal at the point of incidence on the mirror surface is a line which extends through the centre of curvature. Once the normal is drawn the angle of incidence can be measured and the reflected ray can be drawn with the same angle. This process is illustrated with two separate incident rays in the diagram at the right.

4. Image Formation – Virtual Image
An image is a position in space where all the reflected light appears to diverge from. Since light from the object appears to diverge from this location, a person who sights along a line at this location will perceive a replica or reproduction of the actual object. In the case of plane mirrors, the image is said to be a virtual image.

5. Virtual Image
Virtual images are images which are formed in locations where light does not actually reach. Light does not actually pass through the location on the other side of the mirror; it only appears to an observer as though the light were coming from this position. Whenever a mirror (whether a plane mirror or otherwise) creates an image which is virtual, it will be located behind the mirror where light does not really pass

6. Real Images
When a real image is formed, it still appears to an observer as though light is diverging from the real image location. Only in the case of a real image, light is actually passing through the image location.

7. Suppose that a light bulb is placed in front of a concave mirror at a location somewhere behind the centre of curvature (C). The light bulb will emit light in a variety of directions, some of which will strike the mirror.
Each individual ray of light which strikes the mirror will reflect according to the law of reflection.

8. Upon reflecting, the light will converge at a point
Upon reflecting, the light will converge at a point. At the point where the light from the object converges, a replica or reproduction of the actual object is created; this replica is known as the image.
Once the reflected light rays reach the image location, they begin to diverge . The point where all the reflected light rays converge is known as the image point.

9. Viewing the Image
Not only is it the point where light rays converge, it is also the point where reflected light rays appear to an observer to be diverging from. Regardless of the observer's location, the observer will see a ray of light passing through the real image location. To view the image, the observer must line her sight up with the image location in order to see the image via the reflected light ray.

10. Moved Image
If the light bulb is located at a different location, the same principles apply. The image location is the location where reflected light appears to diverge from. By determining the path which light from the bulb takes after reflecting from the mirror, the image location can be identified. The diagram depicts this concept.

11. Image Formation for Convex Mirrors
The diagram shows an object placed in front of a convex mirror.
Several rays of light emanating from the object are shown approaching the mirror and subsequently reflecting. Each observer must sight along the line of the reflected ray to view the image of the object. Each ray is extended backwards to a point of intersection - this point of intersection of all extended reflected rays indicates the image location of the object.

12. The image in the diagram is a virtual image
The image in the diagram is a virtual image. Light does not actually pass through the image location. It only appears to observers as though all the reflected light from each part of the object is diverging from this virtual image location.

13. Refraction Rule for a Converging Lens
Any incident ray travelling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.

14. Refraction Rules for a Converging Lens
Any incident ray travelling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.
Any incident ray travelling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.

15. Refraction Rule for a Diverging Lens
Any incident ray travelling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its extension will pass through the focal point).

16. Refraction Rules for a Diverging Lens
Any incident ray travelling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its extension will pass through the focal point).
Any incident ray traveling towards the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.

18. Object Outside 2F