Geometric Optics Chapter 2 PDF

Chapter 2 Geometrical Optics What is Light? What is Light? Light is a Form of Energy that travels away from the source producing it at a Speed of 300 000 000 m s-1. Worked Example: The Sun is 1.5 x 1011 m from earth 1. How long does it take light to get from the sun to the earth. Speed...

Chapter 2 Geometrical Optics What is Light? What is Light? Light is a Form of Energy that travels away from the source producing it at a Speed of 300 000 000 m s-1. Worked Example: The Sun is 1.5 x 1011 m from earth 1. How long does it take light to get from the sun to the earth. Speed of light = 3 x 108 m s-1  Without light you cannot see You can see both luminous and non-luminous objects luminous Non- luminous Converting Light Energy to Electrical Energy How do you prove that light is energy? Crooke’s Radiometer converts Light Energy into Kinetic Energy. Or use a solar panel. How can you prove that light travels in straight lines? Draw Ray Diagrams for a: parallel beam converging beam diverging beam Each of these lines is called a ray What is Reflection of Light? The bouncing of light from the surface of an object is called Reflection. There are two kinds of reflection: Diffuse Reflection Regular Reflection What is Diffuse Reflection? When light strikes a matt surface (non smooth surface), the reflected light is scattered in all directions. This is Diffuse Reflection. Most everyday objects are visible to you by light which has been diffusely reflected from them.  What is Regular Reflection? If the surface that the light strikes is silvered and polished smooth, i.e. if it is a mirror, the light is reflected as shown. This is called Regular Reflection. Key words NB all angles are measured Normal at the point from the of incidence Normal line Regular reflection  What is a “normal”? A line or vector perpendicular to a surface Test your self Label parts a, b and c w, x, y or z Which is the angle of incidence w, x, y or z Which is the angle of reflection b: a: c: (2 words) x y w z State The Laws of Reflection of Light. State The Laws of Reflection of Light Law 1: The incident ray, the normal at the point of incidence and the reflected ray all lie in the same. plane. Law 2: The angle of incidence is equal to the angle of reflection. i = r Law 1: The Incident Ray, the Normal at the point of incidence and the Reflected Ray all lie in the Same Plane. Law 2: Angle of Incidence = Angle of Reflection. i = r NB all angles are measured from the Normal Experiment: Demonstrate the laws of reflection See next two slides  To demonstrate the 1st Law of Reflection Set up the equipment as Sheet of Paper shown. With a pencil, mark the position of the ray before and after it strikes the mirror. Mark the position of the mirror. Remove the mirror and draw in the normal at the point of incidence. With a protractor measure the angle of incidence (i) and the angle of reflection (r). Repeat the experiment for different values of i. It will be found that the Angle of Incidence is equal to the Angle of Reflection. To demonstrate the 2nd Law of Reflection It is also found that the reflected ray will be travelling parallel to the paper, i.e. it will not be heading up from the paper or heading into the paper. It will be in the same plane as the incident ray and the normal. Sheet of Paper How is an Image formed in a plane mirror? Object P Image Q Virtual image of P All of the reflected rays appear to come from Q Draw a ray diagram showing how the image of a point A is formed in a plane mirror. A What is a virtual image? What is a Virtual Image? What is a virtual image? What is a Virtual Image? A Virtual Image is an image formed by the Apparent Intersection of Rays. A virtual image cannot be formed on a screen. Describe the image in a plane mirror. The image in a plane mirror is: Virtual Upright The same distance behind the mirror as the object is in front of the mirror Lateral Inversion The image of a right hand in a plane mirror is a left hand. The front of an ambulance has “ ” written on it. A driver ahead will see “AMBULANCE” in the rear view mirror. Uses of a plane mirror 1. Applying makeup or shaving 2. The Periscope What is Parallax? The apparent movement of one object relative to another due to the motion of the observer. The object which is further away appears to move with the observer. the bird is in line with the soccer ball A B the bird is in line with the rugby ball  Using Parallax in determining position The observer moves from side to side without moving the objects. The object which is further away appears to move with the observer.  Using Parallax in determining position Then the objects are the same distance from the observer, Their relative positions do not change when the observer moves.  Locate an image in a plane mirror using the method of no parallax Position the search pin at the location where there is no parallax between the image and the search pin  How can parallax be used to measure the distance to a star? spring earth star distant sun galaxies autumn Calculate the distance with trigonometry. Only works for stars up to 400 light years away. https://www.scienceabc.com/nature/universe/how-do-you-measure-the-distance-to-a-star.html When taking measurements, you can get parallax errors Parallax errors in a moving coil meter Page 12 Page 13 Checklist continued Various definitions of Parallax The apparent movement of one object relative to another due to the motion of the observer. The object which is further away appears to move with the observer. displacement or difference in the apparent position of an object viewed along two different lines of sight (W) A change in the apparent position of an object relative to more distant objects, caused by a change in the observer's line of sight towards the object. the apparent displacement or the difference in apparent direction of an object as seen from two different points not on a straight line with the object the change in an object's relative position as seen from two different positions