Reflection of Light

1. Reflection of Light

2. What is light? • A form of energy • Travels at a speed of 3 x 108 m/s • Light can either be directly obtained from a luminous source or reflected off a non-luminous source into our eyes. • The wave-particle duality of light means it possesses both wave-like or particle-like properties. • Light travels in a straight line

3. Reflection of light • When a ray of light strikes any surface, it changes its direction of travel by following the law of reflection.

4. Laws of Reflection The laws of reflection state that • The incident ray, the reflected ray and the normal all lie in the same plane • The angle of incidence is equal to the angle of reflection

5. Types of reflection

6. Specular and diffused reflection activity • Go to http://micro.magnet.fsu.edu/primer/java/reflection/specular/index.html

7. Specular (Regular) reflection • Parallel light rays of an object fall on the surface at the same angle of incidence. • As the surface is smooth, the angles of reflection of all the rays are parallel. • A clear image is formed • Eg. Mirrors or water surface of calm lakes.

8. Diffused reflection • Parallel light rays of an object fall on the surface at different angles of incidence as the surface is rough. • The rays will all reflect off the surface at different angles and no clear image will be formed • E.g. sandy surface or rippled water bodies

9. Characteristics of a plane mirror image • Same size as the object • Laterally inverted • Upright • Virtual (represented by dotted line) – virtual image is an image that cannot be projected or captured on a screen. It is produced by rays which seem to come from the image but do not actually pass through it. • Distance of the image from the mirror is equal to the distance of the object from the mirror.

10. Constructing Ray Diagrams Textbook – page 224 - 225 • Measure accurate the perpendicular distance between object O and the mirror surface • Locate image I by marking off the same distance behind the mirror

11. Constructing Ray Diagrams Join the image I to the eye by drawing the straight lines as shown. • Use dotted line for the lines behind the mirror surface • Use solid lines for lines that are in front of the mirror surface

12. Constructing Ray Diagrams Join the object O to the points of incidence on the mirror surface, that is the surface touching the plane mirror. • Draw the incident rays from the object O to the points of incidence on the mirror surface. By doing so, you can see that for each ray, the angle of incidence and angle of reflection are equal.

13. Applications of mirrors • Blind corners • A convex mirror is used in the blind corner mirror to widen the angle of view

14. Applications of mirrors • Instrument scales • A plane mirror is used in the instrument to avoid parallex error. If the eye is vertically above the pointer, the image of the pointer cannot be seen.

15. Applications of mirrors • Magnified mirror • A concave mirror in a dentist’s mirror magnifies the upright images.

16. Applications of mirrors • Reflector • A concave mirror is used in car headlights and torchlights as reflectors. It produces a beam of parallel light rays so that the light rays can travel for a longer distance.

17. Applications of mirrors • Periscope • Two plane mirrors are used in the periscope to reflect and change the direction of light rays