Light - 03 - Reflection - Drawing Images

6.4 Drawing Images ◼ ◼ Recall, light rays are reflected from surfaces according to the laws of reflection Note: ◼ ◼ when an object & its image are drawn in mirrors, the object is assumed to be producing light rays itself In fact, light rays come from a source & are reflected off the object Image: ◼ ◼ ◼ Please Write this ☺ Is a representation of an object. Produced by *either* the convergence of light rays originating from the object *or* from the extension of these rays. Can be: ◼ real or virtual ◼ smaller or larger ◼ upright or inverted ◼ ◼ Real Images: ◼ Rays actually converge Virtual Images: ◼ Rays appear to come from common point Real = inverted always! Virtual = upright always! Please Write this ☺ Plane Mirrors: ◼ Images: ◼ ◼ ◼ are virtual b/c the rays appear to emanate from behind the mirror are upright are same size but laterally inverted (flipped L-R) Magnification: ◼ Please Write this ☺ Is the ratio between the image & object’s height or distance hi di M = =− ho do hi M= ho di M =− do ◼ Ex. Camera Please Write this ☺ Image is always inverted & real hi di Camera do ho Object Ex. Please Write this ☺ Calculate the image height of an 8.0 m tree which is 80.0 m away from a 20.0 cm pinhole camera. Also state magnification. hi di =− ho do hi M= ho hi 0 .2 =− 8 80 hi = −0.020m − 0.02 M = 8 M = −0.0025 Ex. Calculate the height of a building 300.0 m away from the pinhole that produces an image 3.0 cm high in a 5.0 cm pinhole camera. hi di − 0.03 0 . 05 =− = − ho do h 300 o h0 = 1.8 • 10 m 2 Please Write this ☺ Locating Images in Plane Mirror: Image ◼ ◼ Object ◼ ◼ Draw a line from the object perpendicular to the mirror and continue it behind the mirror. Measure the distance from the object to the mirror. Match the distance behind the mirror This is the position of the image. Please Write this ☺ Locating Images in Plane Mirror: Image Image will be seen here Observer Object Draw the ray diagram … ◼ Join the observer’s eye to the image with a solid line infront and a dashed line behind. ◼ Join the object to the point of incidence with a solid line. Ex Who can see the object reflected in the mirror? Image Note: draw broken lines behind mirror A Object B C D E Please Write this ☺ 6.5 Curved Mirrors – terminology: Focal Point (F): Focal length (f): point halfway between C & pole, situated on principal axis distance between F & pole f Principal Axis Radius of Curvature (r): distance between C & pole r = 2f Centre of Curvature (C): centre of the sphere C F r P Pole/Vertex: centre of the curved mirror Concave Mirror: 1st Principal Ray – Parallel to Principal Axis: PA C F Note: They all reflect through F 2nd Principal Ray – Through Focal Point: PA C F Note: They all reflect parallel to the principal axis 3rd Principal Ray – Through Centre of Curvature: PA C F Note: They all reflect back through C Please Write this ☺ Principal Rays Concave Mirror: ◼ Three specific light rays, leaving object tip: ◼ ◼ ◼ 1st: 2nd: 3rd: in parallel to PA, out through F in through F, out parallel to PA in and out through the C Using principal rays, predict the location of the reflected image. PA Note: Image is smaller, inverted & real C F Using principal rays, predict the location of the reflected image. C PA Note: Image is larger, upright & virtual F ◼ Images formed by concave mirrors: ◼ Real, inverted & smaller ◼ ◼ Real, inverted & same size ◼ ◼ Object between C & F No image ◼ ◼ Object at C Real, inverted & larger ◼ ◼ Object beyond C Object at F Virtual, upright & larger ◼ Object between F & P Please Write this ☺ Convex Mirror: 1st Principal Ray – Parallel to Principal Axis: PA F Note: All reflections appear to come from the focal point C 2nd Principal Ray – Pass through Focal Point: PA F Note: They all reflect parallel to the principal axis C 3rd Principal Ray – Pass through Center Curvature: PA F Note: All reflections appear to come from the centre of curvature C Please Write this ☺ Principal Rays Convex Mirror: ◼ Three specific light rays, leaving object tip: ◼ ◼ ◼ 1st: 2nd: 3rd: in parallel to PA, out as if from F in towards F, out parallel to PA in toward and out as if from C Using principal rays, predict the location of the reflected image. PA Note: Image is smaller, upright & virtual F C Using principal rays, predict the location of the reflected image. PA Note: Image is smaller, upright & virtual F Can solve for magnification using hi/ho C ◼ Images formed by convex mirrors: ◼ Virtual, upright & smaller ◼ Object at any position HW: pg 54 #2, 4, 7 & 9 pg 70 #1, 2