The angle of incidence in the water is approximately 39°. At this angle, the light refracts out of the water into the surrounding air bending away from the normal. The angle of refraction in the air is approximately 57°. These values for the angle of incidence and refraction are consistent with Snell's Law. Join photographer Nicholas on his expedition to Antarctica to photograph the wildlife. In this simulation, you will learn about the wave-like behaviors of light. When light travels from one medium into another, the rays can reflect off of the surface. Depending on the angle and the media, the light can also refract. Lay the mirror flat on the table with the shiny side up. Hold the flashlight at an angle pointing down toward the mirror. Explain to students that the light will be reflected off the mirror. Their task is to use the construction paper to catch the reflected light in order to pinpoint exactly where it goes.The Plane Mirror Images simulation blends an interactive Tutorial with an interactive simulation. Students will learn about the law of reflection and how it can be used to determine the location and characteristics of an image formed by a plane mirror.Bending Light 1.1.29 - PhET Interactive Simulations The light rays from an actual object bounce off the mirror to give a virtual image. With a flat mirror, the real object and the virtual object are symmetric and appear to be at the same distance on either side of the plane of the mirror. Symmetry rules at work in the reflection process explain how an image is formed by a plane mirror. Object A ...Reflection from a Mirror. Update your browser! Adjust the angle of the mirror and see what happens to the reflected beam! Determine the angle when each observer can see the light. Simulation created Steven Sahyun, University of Wisconsin - Whitewater using code modified from Andrew Duffy's Friction on an incline simulator. December 19, 2018. 24. Look at the surface where the light exits from the material to the air, as you change the color of the ray of light from blue toward red, how does the refracted angle change? Select white light and dark background by clicking the last icon on: 25. What is the name of the physical phenomenon effecting the white light that you are observing ?This is a simulation to illustrate the processes involved in the formation of images in plane mirrors. When the control points are visible, you can move the object (the blue arrow), the four points where the (blue) incident rays strike the mirror, as well as the two ends of the mirror itself.Description. This is a visual simulation of the reflection of a wave pulse. Use the check boxes choose between a fixed end (bouncing off a more rigid medium) or a free end (bouncing off a less rigid medium). Use the other check boxes to show or hide the undisturbed incident and reflected waves, so that you can see how their superposition causes ...Bending Light 1.1.29 - PhET Interactive SimulationsThe refractive index is a property of a medium through which light can pass. Its value is calculated from the ratio of the speed of light in vacuum to that in the medium. For example, the refractive index of glass is 1.516 and that of water is 1.333. The amount of bending of light during refraction depends on the difference between the ...Jul 21, 2020 · In/Post-Class Activity, Bending Light, PhET. Description. This is a 60 to 90 min. worksheet related to the concept of refraction and reflection with conceptual questions and simulations activities. Students can observe, examine, explore and connect the simulations to the concepts and would have a better understanding of bending/refracting light ... https://phet.colorado.edu/sims/html/bending-light/latest/bending-light_en.html Bending Light 1.1.29 - PhET Interactive SimulationsFounded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery. Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery.Then follow it up with the Concept Checkers: Our Refraction simulation is now available with two Concept Checkers - one focuses on refraction and the direction of bending; it complements Activity #1 (above). The other focuses on total internal reflection and the critical angle; it complements Activity #3 (above). Do the simulation.Lay the mirror flat on the table with the shiny side up. Hold the flashlight at an angle pointing down toward the mirror. Explain to students that the light will be reflected off the mirror. Their task is to use the construction paper to catch the reflected light in order to pinpoint exactly where it goes.oPhysics. Kinematics. Polarization of Light. Description. This is a simulation intended to help visualize polarization. A polarizing filter has a particular transmission axis and only allows light waves aligned with that axis to pass through. In this simulation unpolarized waves pass through a vertical slit, leaving only their vertical components.Although light is an everyday phenomenon that we constantly observe, a numerous researches have reported that students often displayed learning difficulties and hold unscientific understanding on physics concepts of light wave. To address the situation, inquiry-based learning process with a support of computer simulation has been proved its benefits on development of student’s conceptual ...Science; Physics; Physics questions and answers; In this activity students will be exploring reflection of light in a plane mirror using the "Bending Light" PhET simulation.cal simulation of light scattering by multiple wavelength-sized particles near or between planar interfaces. It im-plements the superposition T-matrix method [15, 16, 17] Krzysztof Czajkowski and Dominik Theobald contributed equally to this work. Figure 1: Artistic visualization of a Gaussian beam scattered by multiple particles on a substrate. Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery.Enhance productivity with 3DOptix, Optical design and Simulation software. Ray Optics describes light propagation in terms of “rays” and is commonly concerned with how light is propagated, reflected, and refracted and the formation of images. The “ray” in geometric optics is an abstraction, or “instrument”, which can be used to ... S3P-2-07 Summarize the early evidence for Newton’s particle model of light. Include: propagation, reflection, refraction, dispersion S3P-2-08 Experiment to show the particle model of light predicts that the velocity of light in a refractive medium is greater than the velocity of light in an incident medium (vr > vi).Description Simulation of image formation in concave and convex mirrors. Move the tip of the Object arrow or the point labeled focus. Move the arrow to the right side of the mirror to get a convex mirror.Reflection of light (and other forms of electromagnetic radiation) occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface. The simplest example of visible light reflection is the surface of a smooth pool of water, where incident light is reflected ... Simulate the reflection of light on a mirror. Mirror (Curved) A mirror whose shape is curved. Can be circular, parabolic, or defined by a custom equation y = f (x). Ideal curved mirror The idealized "curved" mirror which obeys exactly the mirror equation (1/p + 1/q = 1/f). The focal length (in pixels) can be set directly. Beam Splitter Reflection of light (and other forms of electromagnetic radiation) occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface. This tutorial explores the incident and reflected angles of a single light wave impacting on a smooth surface.Total Internal Reflection. This 1.5-minute video features a demonstration in which a beam of light is directed into a hemicylindrical block of glass. The light approaches along the curved side of the cylinder along the radial line so that there is no refraction upon entering the block. Refraction occurs at the flat edge of the block. White light is made up of light rays with different wavelengths which we see as various colors. When light refracts, the amount of bending depends upon the light's wavelength. It is maximum for violet and minimum for red. Hence white light splits into different colored rays, each with different amount of bending, when passing through a prism. oPhysics. Kinematics. Polarization of Light. Description. This is a simulation intended to help visualize polarization. A polarizing filter has a particular transmission axis and only allows light waves aligned with that axis to pass through. In this simulation unpolarized waves pass through a vertical slit, leaving only their vertical components. Join photographer Nicholas on his expedition to Antarctica to photograph the wildlife. In this simulation, you will learn about the wave-like behaviors of light. When light travels from one medium into another, the rays can reflect off of the surface. Depending on the angle and the media, the light can also refract. Reflection of Light In this activity students will be exploring reflection of light in a plane mirror using the “Bending Light” PhET simulation. Open the simulation by clicking on the link: Learning Objectives By the end of these activities it is hoped that students will have an acquired the following skills: • Following explicit instructions to gain acquired knowledge • Understand ...Then follow it up with the Concept Checkers: Our Refraction simulation is now available with two Concept Checkers - one focuses on refraction and the direction of bending; it complements Activity #1 (above). The other focuses on total internal reflection and the critical angle; it complements Activity #3 (above). Do the simulation.Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light. The four methods discussed on this page are: Polarization by Transmission.The Plane Mirror Images simulation blends an interactive Tutorial with an interactive simulation. Students will learn about the law of reflection and how it can be used to determine the location and characteristics of an image formed by a plane mirror.6.3.2: Refraction Simulation. The ratio of the speed of light in a material to the speed in a vacuum ( c = 3.0 ×108 m/s c = 3.0 × 10 8 m/s) is called the index of refraction; n = c/v n = c / v where v v is the speed of light in the medium. In this simulation we will investigate the effects of a change in the speed of a wave as it moves from ...The Plane Mirror Images Interactive is a skill-building tool that allows the user to explore the formation of images in plane mirrors. It makes a wonderful complement to lab activities on the law of reflection and the characteristics of plane mirror images. The Interactive takes a Tutorial approach to these topics.How does a lens or mirror form an image? See how light rays are refracted by a lens or reflected by a mirror. Observe how the image changes when you adjust the focal length of the lens, move the object, or move the screen.The light ray reflecting away from the mirror is called the reflected ray. What is the Normal, Angle of Incidence and Reflection? A normal is a line drawn perpendicular to the reflective surface at the point where incident ray hits the surface. The refractive index is a property of a medium through which light can pass. Its value is calculated from the ratio of the speed of light in vacuum to that in the medium. For example, the refractive index of glass is 1.516 and that of water is 1.333. The amount of bending of light during refraction depends on the difference between the ...Mar 25, 2020 · Download all files as a compressed .zip. Title. Virtual Lab - Investigating Refraction of Light. Description. Three short virtual lab investigations. 1) Validating Snell's Law, 2) Describing the intensity of the reflected and refracted rays and 3) determining the refractive index of a mystery metal. Subject. Conclusion: when light passes from a transparent medium A to another transparent medium B where n A > n B: 1. if then refraction will take place. 2. if then the refraction angle is 90° (grazing angle). if then total internal reflection will take place and (where is the angle of reflection and not refraction).REFLECTION AND REFRACTION SIMULATION. The purpose of this activity is to study how light reflects off a shiny surface, and how it refracts when entering a transparent material. Submit your answers using Blackboard. The angle of incidence and reflection are labeled i and r respectively.Oct 26, 2010 · Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery. In this Interactive, learners can drag a candle to various positions in front of a curved mirror and quickly observe the characteristics of the images that are formed. It's that simple; no dripping candle wax, no mess to clean up, just pure physics. Now available with a Concept Checker. The lighting simulation software is primarily used in illumination design to simulate and optimize light pipes, and light guides, and non-imaging lenses and mirrors. TracePro is also a powerful tool for analysis of aspects of imaging systems such as stray light analysis and polarization effects. With its full set of features, designers can ... lack of medium) for light, 𝑣<𝑐 for anything that isn’t vacuum. This means that 𝑛>1, and the larger 𝑛 is, the slower light travels through the medium. In the third video, green laser light passes from air to a piece of acrylic. The index of refraction for the acrylic is 3) (1 point) Calculate the speed of light 𝑣 as it travels Total Internal Reflection. This 1.5-minute video features a demonstration in which a beam of light is directed into a hemicylindrical block of glass. The light approaches along the curved side of the cylinder along the radial line so that there is no refraction upon entering the block. Refraction occurs at the flat edge of the block. How does a lens or mirror form an image? See how light rays are refracted by a lens or reflected by a mirror. Observe how the image changes when you adjust the focal length of the lens, move the object, or move the screen. Join photographer Nicholas on his expedition to Antarctica to photograph the wildlife. In this simulation, you will learn about the wave-like behaviors of light. When light travels from one medium into another, the rays can reflect off of the surface. Depending on the angle and the media, the light can also refract. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So if the media (or its properties) are changed, the speed of the wave is changed. Thus, waves passing from one medium to another will undergo refraction. Refraction of sound waves is most evident in situations in which the sound ...Make a whole rainbow by mixing red, green, and blue light. Change the wavelength of a monochromatic beam or filter white light. View the light as a solid beam, or see the individual photons.Three short virtual lab investigations. 1) Validating Snell's Law, 2) Describing the intensity of the reflected and refracted rays and 3) determining the refractive index of a mystery metal. Subject. Physics. Level. High School, Undergrad - Intro. Type. Guided Activity, Lab. Duration.Oct 26, 2010 · Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery. Ellipse Reflection Model. Move the points. Adjust number of segments. Press Play. This is a computer model of how sound (or light, etc) reflects inside an ellipse. Points "F" and "G" are the focus points of the ellipse. Example: Stand at one focus point in an elliptical room. A friend could stand at the other focus point and whisper: you would ... 24. Look at the surface where the light exits from the material to the air, as you change the color of the ray of light from blue toward red, how does the refracted angle change? Select white light and dark background by clicking the last icon on: 25. What is the name of the physical phenomenon effecting the white light that you are observing ?cal simulation of light scattering by multiple wavelength-sized particles near or between planar interfaces. It im-plements the superposition T-matrix method [15, 16, 17] Krzysztof Czajkowski and Dominik Theobald contributed equally to this work. Figure 1: Artistic visualization of a Gaussian beam scattered by multiple particles on a substrate.Reflection of light (and other forms of electromagnetic radiation) occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface. This tutorial explores the incident and reflected angles of a single light wave impacting on a smooth surface.Enhance productivity with 3DOptix, Optical design and Simulation software. Ray Optics describes light propagation in terms of “rays” and is commonly concerned with how light is propagated, reflected, and refracted and the formation of images. The “ray” in geometric optics is an abstraction, or “instrument”, which can be used to ... In this video You will learn the basics of refraction of light. Here the concept of total internal reflection (TIR) and Critical Angle has also been discusse...Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So if the media (or its properties) are changed, the speed of the wave is changed. Thus, waves passing from one medium to another will undergo refraction. Refraction of sound waves is most evident in situations in which the sound ...In this Interactive, learners can drag a candle to various positions in front of a curved mirror and quickly observe the characteristics of the images that are formed. It's that simple; no dripping candle wax, no mess to clean up, just pure physics. Now available with a Concept Checker.Reflection, refraction and diffraction are all boundary behaviors of waves associated with the bending of the path of a wave. The bending of the path is an observable behavior when the medium is a two- or three-dimensional medium. Reflection occurs when there is a bouncing off of a barrier. Reflection of waves off straight barriers follows the ... Lay the mirror flat on the table with the shiny side up. Hold the flashlight at an angle pointing down toward the mirror. Explain to students that the light will be reflected off the mirror. Their task is to use the construction paper to catch the reflected light in order to pinpoint exactly where it goes.Enhance productivity with 3DOptix, Optical design and Simulation software. Ray Optics describes light propagation in terms of “rays” and is commonly concerned with how light is propagated, reflected, and refracted and the formation of images. The “ray” in geometric optics is an abstraction, or “instrument”, which can be used to ... The subject of this chapter is the reflection and refraction of light—or electromagnetic waves in general—at surfaces. We have already discussed the laws of reflection and refraction in Chapters 26 and 33 of Volume I. Here’s what we found out there: The angle of reflection is equal to the angle of incidence.S3P-2-07 Summarize the early evidence for Newton’s particle model of light. Include: propagation, reflection, refraction, dispersion S3P-2-08 Experiment to show the particle model of light predicts that the velocity of light in a refractive medium is greater than the velocity of light in an incident medium (vr > vi).This is a simple simulation showing the reflection and refraction of a ray of light as it attempts to move from one medium to another. Use the sliders to adjust the index of refraction of each of the two materials, as well as the angle of incidence (the angle between the incident ray of light and the normal to the surface). Light. Light Mixing; Color Pigment Mixing; Polarization of Light; Double Slit Diffraction and Interference; Double Slit Interference; Diffraction Grating Laser Lab; Thin Film interference; Reflection and Refraction; Dispersion of Light; Plane Mirrors; Concave and Convex Mirrors; iPad Spherical Mirror Simulation; Concave and Convex Lenses; Lens ... The Plane Mirror Images Interactive is a skill-building tool that allows the user to explore the formation of images in plane mirrors. It makes a wonderful complement to lab activities on the law of reflection and the characteristics of plane mirror images. The Interactive takes a Tutorial approach to these topics.Enhance productivity with 3DOptix, Optical design and Simulation software. Ray Optics describes light propagation in terms of “rays” and is commonly concerned with how light is propagated, reflected, and refracted and the formation of images. The “ray” in geometric optics is an abstraction, or “instrument”, which can be used to ...How does a lens or mirror form an image? See how light rays are refracted by a lens or reflected by a mirror. Observe how the image changes when you adjust the focal length of the lens, move the object, or move the screen.Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery. PhET waves intro has three animations that link to water waves, sound and light and introduce the terms frequency and amplitude. The water wave animation can also be used to replicate part of the GCSE waves required practical. Measuring the wavelength and speed of water waves using method 2 (can be done using baking trays or other suitable ...This Interactive tool allows the user to explore the reflection and refraction of light at a boundary. Users can choose from some pre-selected materials or choose a customized index of refraction value. Angles of incidence, reflection, and refraction can be measured with a built-in protractor.Hi Students and Teachers! Here is a tutorial on how to run the Reflection and Refraction Simulation. I hope this is helpful. Remember: This is Fine and I Can... Aug 4, 2020 · This is a 60 to 90 min. worksheet related to the concept of refraction and total internal reflection with simulations activities. Students can observe, examine, explore and connect the simulations to the concepts and would have a better understanding of the behaviour of the light rays in prisms with different shapes. Subject Physics The Bending Light simulation (see FigureL20.4, p. 194) enables you to change the angle of incidence of a light ray that crosses the boundary between two transparent materials and then measure the angle of reflection and refraction.Regular and Diffused Reflection. The light gets reflected from the surfaces. Any surface which is polished or in other words is shiny always acts like a mirror. The observation of light bouncing off the surfaces is termed reflection. The light after reflection travels in the same medium from where the ray was incident on the surface.This is a simple simulation showing the reflection and refraction of a ray of light as it attempts to move from one medium to another. Use the sliders to adjust the index of refraction of each of the two materials, as well as the angle of incidence (the angle between the incident ray of light and the normal to the surface). Hi Students and Teachers! Here is a tutorial on how to run the Reflection and Refraction Simulation. I hope this is helpful. Remember: This is Fine and I Can...Aug 13, 2020 · 6.3.2: Refraction Simulation. The ratio of the speed of light in a material to the speed in a vacuum ( c = 3.0 ×108 m/s c = 3.0 × 10 8 m/s) is called the index of refraction; n = c/v n = c / v where v v is the speed of light in the medium. In this simulation we will investigate the effects of a change in the speed of a wave as it moves from ... Oct 26, 2010 · Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery. Using the Interactive. The Plane Mirror Images Interactive is shown in the iFrame below. There is a small hot-spot in the lower-right corner of the iFrame. Dragging this hot-spot allows you to change the size of iFrame to whatever dimensions you prefer. Now available with Task Tracker compatibility. Learn more. Enhance productivity with 3DOptix, Optical design and Simulation software. Ray Optics describes light propagation in terms of “rays” and is commonly concerned with how light is propagated, reflected, and refracted and the formation of images. The “ray” in geometric optics is an abstraction, or “instrument”, which can be used to ...Then follow it up with the Concept Checkers: Our Refraction simulation is now available with two Concept Checkers - one focuses on refraction and the direction of bending; it complements Activity #1 (above). The other focuses on total internal reflection and the critical angle; it complements Activity #3 (above). Do the simulation.By converting our sims to HTML5, we make them seamlessly available across platforms and devices. Whether you have laptops, iPads, chromebooks, or BYOD, your favorite PhET sims are always right at your fingertips.Become part of our mission today, and transform the learning experiences of students everywhere!
Although light is an everyday phenomenon that we constantly observe, a numerous researches have reported that students often displayed learning difficulties and hold unscientific understanding on physics concepts of light wave. To address the situation, inquiry-based learning process with a support of computer simulation has been proved its benefits on development of student’s conceptual .... Caterpillar product line brochure pdf
Simulate the rays and images seen from some position. The blue circle is the observer. Any rays crossing it are considered to be "observed". The observer do not know where the rays actually begin, but may think they begin at some point (s) if they intersect there. The rays are shown in blue, and the point (s) in orange.This is a simple simulation showing the reflection and refraction of a ray of light as it attempts to move from one medium to another. Use the sliders to adjust the index of refraction of each of the two materials, as well as the angle of incidence (the angle between the incident ray of light and the normal to the surface).Bending Light Simulation Bend and Manipulate. Reflection and Refraction ... Details of Reflection and Refraction Demonstration Video. What is a Kaleidoscope? ...Light. Light Mixing; Color Pigment Mixing; Polarization of Light; Double Slit Diffraction and Interference; Double Slit Interference; Diffraction Grating Laser Lab; Thin Film interference; Reflection and Refraction; Dispersion of Light; Plane Mirrors; Concave and Convex Mirrors; iPad Spherical Mirror Simulation; Concave and Convex Lenses; Lens ... Reflection of Light In this activity students will be exploring reflection of light in a plane mirror using the “Bending Light” PhET simulation. Open the simulation by clicking on the link: Learning Objectives By the end of these activities it is hoped that students will have an acquired the following skills: • Following explicit instructions to gain acquired knowledge • Understand ... oPhysics. Select a simulation from one of the above categories or click on a category to see descriptions of the simulations for that category. Hydrogen Energy Levels. This is a simulation of an atomic energy level diagram of the hydrogen atom. Using the Interactive. The Plane Mirror Images Interactive is shown in the iFrame below. There is a small hot-spot in the lower-right corner of the iFrame. Dragging this hot-spot allows you to change the size of iFrame to whatever dimensions you prefer. Now available with Task Tracker compatibility. Learn more. Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations. PhET sims are based on extensive education <a {0}>research</a> and engage students through an intuitive, game-like environment where students learn through exploration and discovery.Launch Interactive. Learners are encouraged to open the Interactive and Explore. An activity sheet is not needed for this Interactive. Our Who Can See Who? simulation is now available with a Concept Checker. Do the simulation. Then follow it up with the Concept Checker. Learners and Instructors may be interested in viewing the accompanying ... The law of reflection states that the angle of reflection (θ r) equals the angle of incidence (θ i), θ r = θ i (1) The normal, incident ray and reflected ray all lie in the same plane (Fig. 1). In this lab, you will study the image formation by plane mirrors using an online simulation (Fig. 2 below). Fig. 1: Reflection of light from a ...This is a simple simulation showing the reflection and refraction of a ray of light as it attempts to move from one medium to another. Use the sliders to adjust the index of refraction of each of the two materials, as well as the angle of incidence (the angle between the incident ray of light and the normal to the surface).The Optics Bench Interactive is shown in the iFrame below. There is a small hot-spot in the lower-right corner of the iFrame. Dragging this hot-spot allows you to change the size of iFrame to whatever dimensions you prefer. Our Optics Bench simulation is now available with a Concept Checker that focuses on Concave Mirrors with this activity. Do ...The Plane Mirror Images simulation blends an interactive Tutorial with an interactive simulation. Students will learn about the law of reflection and how it can be used to determine the location and characteristics of an image formed by a plane mirror..