[PHY] Chapter 13 - Light

DARRELL ER (COPYRIGHTED) © TOPIC 13: LIGHT DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

REFLECTION LAW OF REFLECTION RA Y DIAGRAM & PLANE MIRROR IMAGE KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

LAW OF REFLECTION 1) The incident ray, the reflected ray, and the normal at the point of incidence all lie on the same plane. 2) The angle of incidence, i, is equal to the angle of reflection, r. LAWS OF REFLECTION DARRELL ER (COPYRIGHTED) ©

RA Y DIAGRAM STEP BY STEP GUIDE FOR RAY DIAGRAM STEP 1 Locate the image. It will be the same distance from the mirror as the object’s distance from mirror. STEP 2 Draw light rays from image to the eyes. (Dotted lines in virtual plane and solid lines in for outside mirror.) STEP 3 Draw light ray from object to mirror, meeting at the reflected rays. STEP 4 Add in the arrows if you haven’t & draw the normal at the point of reflection. DARRELL ER (COPYRIGHTED) © M Image Object M Image Object M Image Object M Image Object

CHARACTERISTICS OF PLANE MIRROR IMAGE Images in a plane mirror are: - Image is virtual. - Image is upright. - Image is same size as object. - Image is laterally inverted. - Image will be same distance from the mirror as the object is from the mirror. RA Y DIAGRAM DARRELL ER (COPYRIGHTED) ©

REFRACTION LAW OF REFRACTION REFRACTIVE INDEX KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

WHY DO LIGHT RAYS REFRACT? WHY DO LIGHT RAYS UNDERGO REFRACTION? Light rays bend due to the difference in speed of light in different optical mediums. IMAGINE THIS SCENARIO You are trying to get from point A to point B. You walk faster on land than swim in water. What path will allow you to reach point B in the shortest amount of time? You will not just simply travel in a straight line because that means spending an equal amount of time in water and on land when you travel faster on land. Given that you walk faster on land, you would cut short the distance you swim in water and attempt to get on land as soon as possible. You will probably travel in a path as shown above. Light behaves in the same way, taking the fastest path. Light rays bend due to the difference in speed of light in different mediums. water land A B DARRELL ER (COPYRIGHTED) ©

LAW OF REFRACTION 1) The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane. 2) For light passing through any two mediums, the ratio of sin i / sin r is a constant (refractive index). BENDING OF LIGHT RAYS When light travel from a less dense medium to a denser medium, the refracted ray will bend towards the normal. When light travel from a denser medium to a less dense medium, the refracted ray will bend away from the normal. LAW OF REFRACTION *See if you are able to visualise the example from the previous page to the 2 refraction diagrams shown here. (Strongly suggest you understand this instead of memorizing.) DARRELL ER (COPYRIGHTED) © Less dense to denser medium Denser to less dense medium Speed of light Decreases Increases Light ray Towards normal Away from normal Diagram Optically less dense medium Optically dense medium Bends towards normal Optically denser medium Optically less dense medium Bends away from normal

FORMULAS FOR REFRACTIVE INDEX n = sin i / sin r, where i is angle of incidence & r is angle of refraction. n = speed of light in vacuum* (c) / speed of light in medium (v) *speed of light in vacuum is 3 x 108 ms-1 n = real depth / apparent depth Note that refractive index, n, should never be smaller than value 1. REFRACTIVE INDEX DARRELL ER (COPYRIGHTED) © Medium Refractive index, n Vacuum 1.00 Air 1.003 Water 1.33 Glass 1.50 Diamond 2.42