Light is a very complex phenomenon, but in many situations its behavior can be understood with a simple model based on rays and wave fronts. A ray is a thin beam of light that travels in a straight line. A wave front is the line (not necessarily straight) or surface connecting all the light that left a source at the same time. For a source like the Sun, rays radiate out in all directions; the wave fronts are spheres centered on the Sun. If the source is a long way away, the wave fronts can be treated as parallel lines.
The law of reflection
Objects can be seen by the light they emit, or, more often, by the light they reflect. Reflected light obeys the law of reflection, that the angle of reflection equals the angle of incidence.
Law of Reflection: In the diagram at left, a light ray PO strikes a vertical mirror at point O, and the reflected ray is OQ. By projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of incidence, θi and the angle of reflection, θr. The law of reflection states that θi = θr, or in other words, the angle of incidence equals the angle of reflection.
Laws of reflection:
The laws of reflection are as follows:
- The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
- The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.
- The reflected ray and the incident ray are on the opposite sides of the normal.
Mirrors with curved surfaces can be modeled by ray tracing and using the law of reflection at each point on the surface. For mirrors with parabolic surfaces, parallel rays incident on the mirror produce reflected rays that converge at a common focus. Other curved surfaces may also focus light, but with aberrations due to the diverging shape causing the focus to be smeared out in space. In particular, spherical mirrors exhibit spherical aberration. Curved mirrors can form images with magnification greater than or less than one, and the image can be upright or inverted. An upright image formed by reflection in a mirror is always virtual, while an inverted image is real and can be projected onto a screen.
|Grades||Activities & Simulations (click underlined simulations to view in below window)|
|4th - 8th||Plain mirrors at angles – Multiple images, Look into the mirror and trace the path, Plane Mirror – Image characteristics, Ray diagram for Plane Mirror, What length of the mirror is required
|8th-12th and above||Build yourself – Ray diagram construction- Convex mirror, Convex mirror – Image characteristics, Convex mirror – Radius of curvature and f, Convex mirror -Size, focal length and Magnification, Build yourself- Ray diagram construction-Concave mirror, Concave Mirror – Image characteristics, Concave mirror -Size, focal length and Magnification, Concave mirror – Radius of curvature and f, Light-Total internal reflection and Fiber optics, Huygens principle – Wave fronts and Reflection, Diffused Reflection, Find the fastest Path, Plane Mirror – Image characteristics, Ray diagram for Plane Mirror, What length of the mirror is required, Plain mirrors at angles – Multiple images, Look into the mirror and trace the path|