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3. Physics Ex-47 Click THE LAW OF REFLECTION When light strikes a surface and is reflected, it changes direction. The direction it takes depends upon the angle it strikes the surface. As illustrated below, a ray of light going towards a surface is called an incident ray while a ray of light which is reflected away from a source is called a reflected ray. The law of reflection says that the angle of the incident ray with the normal equals the angle of the reflected ray (also with the normal).

4. Physics Ex-47 Click By definition, the angle which the incident ray makes with the normal is called the angle of incidence while the angle which the reflected ray makes with the normal is called the angle of reflection. Remember : The angle of incidence (i) is the angle formed by the incident ray and the normal (not the reflecting surface). The angle of reflection (r) is the angle between the reflected ray and the normal. Note that the incident ray, the reflected ray, and the normal are all on the same plane.

5. Physics Ex-47 Click The law of reflection, therefore, simply states that when a ray of light is reflected from a surface, it is reflected in such a direction that the incident angle equals the reflected angle. Using the law of reflection, we can determine the location of images formed by plane mirrors.

6. Physics Ex-47 Back of mirror Object An object is placed in front of a plane mirror. Find the location and characteristics of the image. T A S K Rather than draw an actual object, it is easier to draw the object as an arrow. This way, we can tell if the image is inverted or not. Objects consist of an infinite number of points. And each point has an infinite number of rays radiating outwards. Images also consist of an infinite number of points. Each point on the object has a corresponding point on the image. In locating an image, we take one point on the object and find its corresponding point (location) on the image object. As shown above, we usually take the (extreme) top point and find its corresponding point on the image object. Normal Incident ray Reflected ray Extended ray Incident ray Reflected ray Extended ray We can now draw the image. Since the two reflected rays diverge, we must “extend” them so that they will intersect. There are two steps in finding the image of a plane mirror. NOTE Draw an incident ray slightly upwards towards the mirror. Then draw its reflected ray in accordance with the law of reflection. Step-1 Draw an incident ray slightly downwards towards the mirror, then draw its reflected ray. Step-2 Since we are not given the location of the object, we can select any arbitrary location. Such as right here! Click Where the two reflected rays meet is the image point of the object point.

7. Physics Ex-47 Click Virtual images are formed by extended rays. Real images are formed by reflected rays.

8. Physics Ex-47

9. Eye Mirror Given a plane mirror and the position of an observer’s eye, determine the field of vision. T A S K Field of vision (Any point within this area will be reflected to the observer’s eye as an image point.) There are two steps in finding the field of vision. NOTE Draw a ray from the eye to one end of the mirror. This is the reflected ray. Then, in accordance with the law of reflection, draw the incident ray. Step-1 W e c a n n o w d r a w t h e f i e l d o f v i s i o n. I t i s t h e a r e a b o u n d e d b y t h e m i r r o r a n d t h e t w o i n c i d e n t r a y s. Reflected ray Incident ray Reflected ray Incident ray angle of incidence = angle of reflection Draw a ray from the eye to the other end of the mirror. This is the reflected ray. Then, in accordance with the law of reflection, draw the incident ray. Step-2 Normal Click

10. Physics Ex-47 Eye Mirror Given a plane mirror, a point object (P) and the position of an observer’s eye, determine whether or not the observer can see object point P. TASK P P'P' To determine whether or not the observer can see the given object, we first locate the image of the object. Next, we draw a line from the image point to the observer (eye). If the line intersects the mirror, the observer can see the image. If the line does not intersect the mirror, then the observer cannot see the image. NOTE Object point To find the location of the image point, we start by drawing a line perpendicular to the mirror and extend it beyond the mirror. Perpendicular to mirror Next, since the image distance equals the object distance, we mark off the image point, P‘, along the extended line. Object distance Image distance Image point Finally, we draw a straight line from the observer’s eye to the image point. If this line intersects the mirror, the observer can see the image. If this line does not intersect the mirror, the observer cannot see the image. Look! The line does not intersect the mirror. Conclusion: observer cannot see the image. ANSWER The observer cannot see the image. Click Object distance = Image distance

11. Physics Ex-47 Eye Mirror Given a plane mirror, a point object (P) and the position of an observer’s eye, determine whether or not the observer can see object P. T A S K P P'P' To determine whether or not the observer can see the given object, we first locate the image of the object. Next, we draw a line from the image point to the observer’s eye. If the line intersects the mirror, the observer can see the image. If the line does not intersect the mirror, then the observer cannot see the image. NOTE Object pointPerpendicular to mirrorImage point To find the location of the image point, we start by drawing a line perpendicular to the mirror and extend it beyond the mirror. Object distance Image distance We now draw a straight line from the observer’s eye to the image point. If this line intersects the mirror, the observer can see the image. If this line does not intersect the mirror, the observer cannot see the image. Look! The line does not intersect the mirror. Thus, the observer cannot see the image. ANSWER The observer cannot see the image. Click Object distance = Image distance

13. Physics Ex-47 Question-1 State the Law of Reflection. Click The angle of incidence equals the angle of reflection. Click

14. Physics Ex-47 Question-2 The diagram below represents an object in front of a plane mirror. Click  Note : Diagram not drawn to scale. a) Draw the image. b) How high is the image? 4 cm c) How far is the image from the object? Click 20 cm Click Object Click

15. Physics Ex-47 Question-3 Explain why there is only a lateral (left-right) reversal when we look at ourselves in a plane mirror. Click Because when we turn towards a mirror, we do so by turning about the Y-axis (left-right) and not about the X-axis (top-bottom). Click

16. Physics Ex-47 Question-4 The diagram below illustrates the image of an object produced by a plane mirror. Label the incident ray, the reflected ray and the extended ray. Click Reflected ray Incident ray Extended ray

17. Physics Ex-47 Question-5 Explain how real images are formed and how virtual images are formed. Click Real images are formed by the intersection of reflected rays, virtual images are formed by the intersection of extended rays. Click NOTE As long as there is at least one extended ray, the image is said to be virtual.

18. Physics Ex-47 Question-6 Stefania is 1.5 m tall. Prove that the shortest mirror necessary for Stefania to see her full height is 75 cm (half her height). Click Divide Stefania’s height into two parts, from her eyes to the top of her head and from her eyes to the bottom of her feet. Click Thus, in order for a person to see their full height in a plane mirror, the minimum mirror required is a mirror half their height. Half Stefania’s height

19. Physics Ex-47 Question-7 A beam of light is reflected from a plane mirror such that the angle between the incident ray and reflected ray is 50 o. Draw the beam and calculate the angle of incidence?. Click

20. Physics Ex-47 Question-8 Two mirrors, M 1 and M 2, are at 90 o to each other. As illustrated, a beam of light strikes mirror M 1 with an angle of incidence of 60 o and is reflected by mirror M 2. Complete the diagram and find the angle of incidence of the ray reflected by mirror M 2. Click Angle of incidence of mirror M 2

21. Physics Ex-47 Question-9 Two plane mirrors, M 1 and M 2, are at 60 o to each other as illustrated in the diagram below. A beam of light strikes mirror M 1 with an angle of incidence of 40 o. Complete the diagram and determine the angle of reflection of the beam reflected from mirror M 2 ? Click Angle of reflection of mirror M 2

22. Physics Ex-47 Question-10 Two mirrors are parallel to each other as illustrated in the diagram below. A beam of light strikes the beginning of one mirror at an angle of incidence of 35 o. Complete the diagram and find the number of times the beam is reflected before it emerges from the two mirrors?. Click

23. Physics Ex-247 A) 1 B) 2 C) 3 D) 4 Question-11 What is the angle of reflection for the ray diagram illustrated below? Click REMINDER All angles are measured from the “normal”. Angle of incidenceAngle of reflection

24. Physics Ex-47 Question-12 Stefania wants to install a rear view mirror on her bike. She has a choice of choosing a plane or a convex mirror as illustrated below. Which mirror should Stefania choose in order to obtain the maximum filed of view? Click Observer Answer: Stefania should choose the convex mirror in order to obtain the maximum field of view.

25. Physics Ex-47 Question-13 The following set up consists of a light source, an obstacle, six different locations (labeled 1 to 6) and a target. At which one of the locations can you place a plane mirror so that the light source is reflected to the target? Click To determine the correct location, we draw two lines from each point. One line to the light source and another line to the target. If both lines are unobstructed, that is the point where we place the mirror. Note that only at location 5 can we draw unobstructed lines both to the source and to the target. Thus, we must place the mirror at location 5. No Yes No We now divide the angle between the two lines at location 5 with a bisector. This bisector will be the normal to the mirror. Finally, we draw the mirror perpendicular to the normal (bisector). Mirror If required, using a protractor, we can measure the angle of incidence or the angle of reflection.

26. Physics Ex-47 Question-14 The set up below consists of an object and its shadow cast on a screen by a point light source. Click Determine the position of the light source. A) Point-A B) Point-B C) Point-C D) Point-D Draw a line from the top of the shadow to the top of the object and then extend the line to the light source. This problem illustrates the fact that light travels in a straight line, technically known as rectilinear propagation.

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