Lesson 2: Reflection and Mirrors PDF

## Lesson 2: Reflection and Mirrors ### Word Detect Here are two reference frames for you to work on. Each frame has a given topic. Use the terms from the box and write them in the frame where they belong to. #### Mirrors - concave - plane - law of reflection - sun - principal axis #### Reflect...

## Lesson 2: Reflection and Mirrors ### Word Detect Here are two reference frames for you to work on. Each frame has a given topic. Use the terms from the box and write them in the frame where they belong to. #### Mirrors - concave - plane - law of reflection - sun - principal axis #### Reflection - convex - rough surface - incident ray - center of curvature - virtual image - smooth surface - light - reflected ray - focus - real image ### Hot Concept: Reflection Reflection is a property of light that occurs when light bounces back as it hits a surface. This is the main reason that you are able to see the objects around you. As the light hits a particular object, the reflected light entering our eyes allows us to see the objects. Note that the object reflecting the light need not be the source of the light itself. Some objects are capable of producing their own light, such as the sun and the stars. Other artificial light sources such as lamps and bulbs also give off their lights. The light emitted from the source is radiated in all directions. Light rays travel in straight lines, so when the light from a source hits a barrier or a reflective surface, the light ray is reflected depending on the angle at which it hits the surface. ### Law of Reflection When the light from a source hits a surface, some of the light is reflected back, and others are absorbed. The direction of the reflected light depends on where the incoming light hits the surface of a reflecting object. | | | | |---|---|---| | **Incident light** | **Normal line** | **Reflected light** | | | | | | **Surface** | | | *[Figure 3.12]** Illustration of the incident ray and reflected ray based on the law of reflection. The law of reflection states that the angle of reflection ($θ_r$) is the same as the angle of incidence ($θ_i$). ### Types of Reflection Light rays may strike at any type of surface. Some surfaces are smooth, and others are rough. The law of reflection applies to any surface where the light strikes. When the light strikes a smooth surface, regular reflection happens. In this case, the incident light rays strike the surface in a parallel orientation and are reflected in the same orientation. However, when the incident light rays strike a rough surface, light is reflected in many directions while still following the law of reflection. As a result, diffused reflection happens. *[Figure 3.13]** (a) Regular reflection; (b) diffused reflection ### Image Formation for Reflecting Surfaces Recall that as light strikes a surface, it can be absorbed by the object and get converted to heat, or it may be reflected back as when it hits a reflective surface. Mirrors are reflective surfaces made up of glass. Mirrors can be either plane mirrors or curved mirrors. Plane mirrors are flat surfaces that reflect light and form an image of an object brought in front of it. ### Image Formation in Plane Mirrors Take any object and put it in front of a plane mirror. What do you see in the mirror? You will see the same object in the mirror. However, the image you see seems to come from behind the mirror. Light rays from the objects hit the mirror, and the reflected rays reach the eyes of the observer, allowing the observer to see the image of the object in the mirror. The image appearing at the back of the mirror is a virtual image. Virtual images are those formed behind the mirror. Notice too that the distance of the image to the mirror is the same as the distance of the real object to the mirror. This virtual image is formed by rays formed behind the mirror. The size of the virtual image formed by the plane mirror is exactly the same as the size of the real object. A peculiar thing about plane mirrors is that the images they produce are laterally inverted. This refers to the left-to-right reversal in plane mirrors. Try raising your right hand in front of the mirror and you will see that it's your left hand that is facing you. Graphically, the image formed by plane mirrors can be traced using the ray diagramming technique. This uses at least two rays to locate and describe the image. Here are the steps to locate and describe the image formed by plane mirrors. 1. Locate the image at the back of the mirror using the rule on distance. Note that the object distance and the image distance are the same. 2. Get at least two points from the image and draw a straight line toward the observer's eye. This is following the line-of-sight rule. Use broken lines at the back of the mirror and solid lines in front of the mirror. The solid lines are the reflected rays. The broken lines represent the virtual rays. 3. From the reflected rays, draw the incident ray on the object. Note that the rays should also correspond to the location as it is in the image. ### Checkpoint 1. What is reflection? 2. Differentiate regular reflection from diffused reflection. ### Images Formed by Curved Mirrors Aside from plane mirrors, there are also curved mirrors. Curved mirrors can be either concave or convex. Convex mirrors have their reflective surfaces bent outward, whereas concave mirrors have their reflective surfaces bent inward. Curved mirrors are not entirely spherical. Instead, they are spherical caps, which are pieces cut from a sphere. Curved mirrors also reflect light rays that strike their surfaces. *[Figure 3.14]** Curved mirror 1. Locate the image at the back of the mirror using the rule on distance. Note that the object distance and the image distance are the same. 2. Get at least two points from the image and draw a straight line toward the observer's eye. This is following the line-of-sight rule. Use broken lines at the back of the mirror and solid lines in front of the mirror. The solid lines are the reflected rays. The broken lines represent the virtual rays. 3. From the reflected rays, draw the incident ray on the object. Note that the rays should also correspond to the location as it is in the image. ### Checkpoint 1. Can a plane mirror create a bigger image of the object? Explain your answer. 2. Describe the image formed by plane mirrors. ### Reflect Upon Plane mirrors can also make images of your physical appearance. Why is it important to be comfortable with what you see in the mirror? In concave or converging mirrors, incident light rays are converged or brought to a certain point or focus, whereas in concave or diverging mirrors, light rays are spread out and dispersed by the mirror. Unlike plane mirrors, curved mirrors produce images of different sizes and locations. Using the ray diagram, we can locate and describe the images formed by curved mirrors. At least two rays are needed to locate the image. You can also use a third ray that passes through the focus and is reflected parallel to the principal axis. *[Figure 3.15]** Images formed by (a) concave mirrors and by (b) convex mirrors ### Do It Right Curved mirrors produce good images because of their good focus. ### Big Idea Road safety is very important. Vehicles have side mirrors that are curved. This will give the driver a better view of the other vehicles. ### Let's Organize Fill in the chart with the correct details. | | | | |---|---|---| | **Light Energy** | **is governed by** | **is reflected by** | | **can be** | **produce** | **has 2 types** | | **may be** | **produce different images depending on** | **produce image** | | **images are** | | | ### Reflective Questions 1. Can light always produce an image when it hits a reflective surface? Explain your answer. 2. Can you use a combination of mirrors to produce images? Explain your answer. ### Tech-wise For more additional activities about the different kinds of mirrors, visit the Diwa Learning Town website at http://bit.ly/diwa-SIM10. ### Pushing It Further A. You are an astronomer. You are invited by one of the public schools in your city to conduct an "Astro Camp" in their school. One of the camp activities is sun- and star-gazing using a telescope. The organizers have asked you to briefly discuss the parts of a telescope and their functions. Draw a cross-sectional area of the telescope, showing the mirrors and other parts. The parts should be well-labeled and visible even at a five-meter distance. Your participants are grade 7 students who are very much eager to see the sun and the stars. Your diagram will be evaluated by the organizers to see if it can be reproduced at a bigger scale. Your work will be evaluated according to its imagery, content, and aesthetic quality. B. You are a vlogger who received an award for your video blog (vlog) entitled "The Science of Things." You are once again invited to submit a vlog entry for the same award for this year. This year's theme is "Mirror and Beyond." The vlog episode should be at least 3-5 minutes. It should feature the wonders of mirrors. There should be no more than three people appearing on the vlog at any given time (including yourself). Your vlog will be viewed by a panel of judges for the esteemed competition. It will also be uploaded a day before the competition for the online voting. The judges will rate your work according to the criteria mentioned earlier. Will Zhang has developed X-ray mirrors from a high-quality, stable silicon material, which is capable of giving images. The material is very much lighter than four pairs of heavy mirrors flying on the Chandra X-ray telescope. Zhang and his team will try out this near-mirror technology in a rocket mission to be launched by NASA in 2021. This will be its first demonstration in space. If proven successful, this technology may be used in the Lynx X-ray laboratory. **Source:** https://nasa.gov/feature/goddard/2019/nasa-s-new-lightweight-x-ray-mirrors-ready-for-try-outs-in-space *[Figure 3.17]** Will Zhang ### Checkpoint 1. Differentiate concave mirrors from convex mirrors. 2. Differentiate the images formed by concave mirrors and by convex mirrors. ### Let's Find Out! **Materials:** Pen and paper **Procedure:** Look at table 3.3. Use the ray diagram on a concave lens to complete the table. The focal length of the mirror is 2.5 cm. | Location of Object (cm) | Height of Object (cm) | Location of Image (cm) | Orientation | Type of Image | Size of the Image (cm) | |---|---|---|---|---|---| | 2 | 1 | | | | | | 2.5 | 1 | | | | | | 3 | 1 | | | | | | 3.5 | 1 | | | | | | 4 | 1 | | | | | | 5 | 1 | | | | | **Note:** Draw the mirror on a sheet of paper before answering. Use the focal length. **Guide Questions:** 1. Which object distance produced the biggest image? 2. Which object distance produced the smallest image? 3. Which object distance produced an inverted image? ### Trivia Mirrors can also reflect sound. Where can you find the biggest sound mirror? Hint: It is more than 60 meters wide and is also known as "the ear." ### Big Idea Curved mirrors can produce different types of images. The object distance and the type of curved mirror used produce images of different types, orientations, and sizes. The images formed by curved mirrors can be either real or virtual. Real images are formed in front of the mirror, whereas virtual images are those formed behind the mirror. Real objects can be projected on a screen. The orientation of the image can either be upright or inverted. The size of the image also changes, as it may be smaller or bigger than the actual object. Let us explore the different images formed by concave mirrors using the ray diagram method. See table 3.2. **Table 3.2 Objects Formed by Concave Mirrors** | Object Location | Illustration | Image Location | Orientation | Type | Size | |---|---|---|---|---|---| | At the midpoint of *f* and *v* | | Behind the mirror. | Upright | Virtual | Large | | At the midpoint of *c* and *f* | | In front of the mirror (beyond *c*) | Inverted | Real | Large | | At *c* or at 2*f* | | In front of the mirror (at *c*) | Inverted | Real | Same size as the object | | At *f* | | No image | | | | | At 2*c* | | In from of the mirror (between *c* and *f*) | Inverted | Real | Small | | At infinity | | In front of the mirror (near *f*) | Inverted | Real | Very small | For convex or diverging mirrors, there is no real focus. Convex mirrors always produce upright, virtual images that are smaller than the actual object. The image is located behind the mirror. *[Figure 3.16]** Image formed by convex mirrors Force, Motion, and Energy 123 ==End of OCR for page 11==