Ray Diagraming Mirrors PDF

MIRRORS Lesson 1: Mirror and Reflection of Light The objects that we see can be placed into one of two categories: luminous objects and illuminated objects. Luminous objects are objects that generate their own light such as the sun. Illuminated objects are objects that are capable of reflecting lig...

MIRRORS Lesson 1: Mirror and Reflection of Light The objects that we see can be placed into one of two categories: luminous objects and illuminated objects. Luminous objects are objects that generate their own light such as the sun. Illuminated objects are objects that are capable of reflecting light to our eyes such as the moon. Line of Sight You can only view the object when light from that object travels to your eye. To view an object, you must sight (observe or aim) along a line at that object; and when you do, light will come from that object to your eye along the line of sight. To view the image of an object in a mirror, you must sight along a line at the image. One of the many rays of light from the object will approach the mirror and reflect along your line of sight to your eye. Mirrors are smooth reflecting surfaces, usually made of polished metal or glass that has been coated with some metallic substance. The two types of mirrors are plane mirrors and curved mirrors.  Types of Mirrors ✓ Plane mirror – is a flat mirror that reflects light rays in the same order as they approach the mirror. ✓ Spherical mirror – is a portion of a sphere that is sliced away and then silvered on one of the sides to form a reflecting surface. Concave Mirror Convex Mirror Lesson 2: Reflections on a Plane Mirror When you look directly into a plane mirror, you will see the reflected images of yourself and the objects around you. You can verify this in front of a bathroom mirror. If you turn off the light in the bathroom to make the room completely dark, the image will disappear. The image will only appear when the light is turned back on. The image you see that is upright and appears to be behind the mirror is known as a virtual image. Figure 1 shows how a plane mirror forms the virtual image of a person. Light rays reflected from the person travel out in all directions. They strike the mirror and reflect toward the eye. The reflected rays are in the same line with an apparent path that leads to the image. So, even though the rays are reflected, the brain treats them as if they had come from behind the mirror, where the person’s image appears to be located. Figure 1. Virtual image If you stand in front of a plane mirror and raise your hand, the mirror image will raise its left hand, and the image in front of a plane mirror is said to show the right-left (lateral) reversal relative to the object. However, the object and image’s thumbs are both at the bottom. The image formed by a plane mirror is laterally inverted where the image is the right way up, but the right hand becomes the left hand. The letters of the word AMBULANCE are printed backward and are reversed in sequence so that they appear in the proper orientation and order when seen in a rearview mirror. Figure 2. Example of laterally reversed image  Characteristics of plane mirror images: 1. The image is as far behind the mirror as you are in front of it and it always forms a virtual image. 2. It is upright or erect. The virtual image is the same vertical orientation as the object. 3. The image formed is the same size as the object or also known as unmagnified. 4. The image is laterally reversed. Figure 3. Formation of image in a mirror  Lesson 3: Reflections on Spherical Mirror In contrast to plane mirrors, which produce only one kind of image, spherical mirrors produce a variety of images. Spherical mirrors, which are a kind of curved mirrors, are reflecting surfaces that have the curvature of a sphere. Think of a giant spherical shell (see figure 4) that can reflect from the outside and the inside. Now imagine that you can chop a slice off it like it is a watermelon. This will give you a curved reflecting mirror. If you look on the bumpy side, the mirror you get is called a convex mirror. If you look at what had been the inside of the shell where it came from, you would be looking at a concave mirror (see figure 5). It’s like looking in a “cave”. Figure 4. Spherical Mirror Figure 5. Convex and Concave mirror The mirrors that result from this slice will have the same curvature as the sphere they came from. This curvature is responsible for the way spherical mirrors reflect and produce images. To understand this process, we need to be familiar with a few terms relating to how we draw ray diagrams for curved mirrors. The main reference line called the principal axis is drawn horizontally. Along this line, we measure all the distances we need. The notable points on the principal axis of concave and convex mirrors are: Table 1. Different Parts of Spherical Mirror Concave Mirrors If a hollow sphere is cut into parts and the outer surface of the cut part is painted, then it becomes a mirror with its inner surface as the reflecting surface. This type of mirror is known as a concave mirror. Characteristics of Concave Mirrors Light converges at a point when it strikes and reflects from the reflecting surface of the concave mirror. Hence, it is also known as a converging mirror. When the concave mirror is placed very close to the object, a magnified and virtual image is obtained (Figure 8). However, if we increase the distance between the object and the mirror then the size of the image reduces, and a real image is formed. The image formed by the concave mirror can be small or large or can be real or virtual. Figure 8. Close up image of concave mirrors Ray diagrams can be used to predict the size and orientation of images produced by concave mirrors. To determine the image formed in a curved mirror, create a ray diagram by doing the following rules and steps. Rules for Drawing Ray Diagrams for Concave Mirrors Rule 1: Incident rays that are parallel to the principal axis will pass through the focal point after reflecting off the mirror. *An incident ray is a ray of light that reaches the surface of a mirror. Rule 2: Incident rays that pass through the focal point will become parallel to the principal axis after reflecting off the mirror. (This is the reverse concept of rule 1.) Steps for Drawing Ray Diagrams for Concave Mirrors Step 1: Using rule 1, draw an incident ray line from the top of the object, parallel to the principal axis, to the surface of the mirror, then draw the reflected ray line from the surface of the mirror through the focal point (see example 1 & 2). Note: Example 1: The object is placed Figure 11. Step 1 beyond C. Example 2: The object is placed between F and V. Step 2: Using rule 2, draw an incident ray line from the top of the object, through the focal point, to the surface of the mirror, then draw the reflected ray line from the surface of the mirror, parallel to the principal axis (see example 1). If the object is between the focal point and the mirror, draw the incident ray line as if it is coming from the focal point (see example 2). Figure 12. Step 2 Step 3: The point of intersection between the reflected ray lines is the top of the reflected image (See Example 1). If the reflected ray lines are diverging, use dashed lines to extend them backward until they intersect (See Example 2). If the bottom of the object lies on the principal axis, the bottom of the reflected image will also lie on the principal axis. If the bottom of the object does not lie on the principal axis, repeat steps 1-3 to locate the bottom of the reflected image. Figure 13. Step 3 After creating a ray diagramming for a concave mirror, determine the configuration, magnification, orientation, and the type of image formed. Configuration is referring to the location where the image is formed. Magnification is the size of the image produced by spherical mirrors with respect to the object size. The image is reduced if the image is smaller than the object. If the image is bigger than the object's size, it is magnified. Orientation is used to describe the position of an image formed whether upright or inverted. When the image is formed above the principal axis, the orientation of the image is upright and when the image is formed below the principal axis, the image is inverted. Types of images can be real or virtual. ✓ Real Images - A real image is formed when light rays from an object converge after reflecting off a mirror. It is therefore formed in front of a mirror and can be projected onto a screen. ✓ Virtual Images - A virtual image is formed when light rays from an object diverge after reflecting off a mirror. It is therefore formed behind a mirror and cannot be projected onto a screen. Example 1 Object’s Position: Beyond C Figure 13. Step 3 Conf iguration Magnif ication Orientation Type of (Location of Image) (reduced or magnified) (upright or inverted) Image (real or virtual) Between C and F Reduced Inverted Real Example 2 Object’s Position: Between F and V Conf iguration Magnif ication Orientation Type of (Location of Image) (reduced or magnified) (upright or inverted) Image (real or virtual) Between F and V magnified Upright Virtual Convex Mirrors If the cut part of the hollow sphere is painted from inside, then its outer surface becomes the reflecting surface. This kind of mirror is known as a convex mirror. Characteristics of Convex Mirrors A convex mirror is also known as a diverging mirror as this mirror separates light when they strike its reflecting surface. Virtual, upright, and reduced images are always formed with convex mirrors, irrespective of the distance between the object and the mirror. Uses of Convex Mirrors - Inside buildings - Vehicle mirrors - Security purposes - Magnifying glass Ray diagrams can also be used to predict the size and orientation of images produced by convex mirrors. Rules for Drawing Ray Diagrams for Convex Mirrors Rule 1: Incident rays that are parallel to the principal axis will pass through the focal point after reflecting off the mirror. Rule 2: Incident rays that are directed at the focal point will become parallel to the principal axis after reflecting off the mirror. (This is the reverse concept of rule 1.) Figure 14. Rule 1 Figure 15. Rule 2 Rules for Drawing Ray Diagrams for Convex Mirrors Step 1: Using rule 1, draw an incident ray line from the top of the object, parallel to the principal axis, to the surface of the mirror, then draw the reflected ray line from the surface of the mirror, as if it is originating from the focal point. Step 2: Using rule 2, draw an incident ray line from the top of the object, towards the focal point, to the surface of the mirror, then draw the reflected ray line from the surface of the mirror, parallel to the principal axis. Step 3: Using dashed lines, extend the reflected ray lines backward until they intersect. Example 1 Object’s Position: The object is in C Conf iguration Magnif ication Orientation Type of (Location of (reduced or (upright or Image Image) magnified) inverted) (real or virtual) Between F and V Reduced Upright Virtual Types of Images ✓ Real Images - A real image is formed when light rays from an object converge after reflecting off a mirror. It is therefore formed in front of a mirror and can be projected onto a screen. ✓ Virtual Images - A virtual image is formed when light rays from an object diverge after reflecting off a mirror. It is therefore formed behind a mirror and cannot be projected onto a screen.