Goals : ** state the two laws of reflection ** use the First Law of reflection to locate any image observed in a plane mirror ** explain the difference between specular and diffuse reflection ** state 4 image characteristics for an object viewed in a plane mirror Feb 22 11:22 AM Transmission of light - The Ray Model of Light Light doesn't need a media to travel, but it can travel through media. We can describe a medium based on how well it transmits light: Transparent media transmit so well can see through them (e.g. distilled water, glass) Translucent media transmit some light, disperse some (e.g. frosted glass, some plastics) Opaque media transmit no light (e.g. steel, wood) Rectilinear propagation: light travels in straight lines Ray the path followed by light Beam the path followed by a bundle of rays Converging beam rays come together Diverging beam rays spread apart Parallel beam rays run parallel to each other 1
Optics 4 Plane Mirror Reflection.notebook Uses of Plane Mirrors Car rear view mirror Image is same distance away as object (side mirrors are different) Why is this important? Home decoration Make small rooms seem larger Feb 20 5:30 PM 2
Devices Periscopes, binoculars, SLR cameras, microscopes Feb 20 5:34 PM Terminology: ray diagram: incident ray: reflected ray: normal: a diagram that shows the path of light when it hits an object the incoming ray the outgoing ray (bounces off a surface) a line perpendicular to the mirror angle of incidence: angle of reflection: angle between the incident ray and the normal angle between the reflected ray and the normal Feb 23 11:43 AM 3
Laws of Reflection First law: Angle of incidence = angle of reflection copy the picture below Laws of Reflection Second law: Incident Ray, Reflected Ray and Normal are all in the same plane sketch the picture below (you DON'T need to include the labels) Feb 23 11:50 AM 4
Specular vs. Diffuse Reflection Activity Sep 21 6:39 AM Specular reflection: all rays form equal angles of reflection; often creates glare Diffuse reflection: Regular vs. Diffuse Reflection copy the pictures below rays form varied angles of reflection; softens the light to reduce glare (eg. ceiling) Feb 23 11:47 AM 5
Images in a plane Mirror Plane mirrors ALWAYS have the same 4 basic characteristics... but first let us look at SALT. SALT is a method to remind yourself that you need to record the image characteristics of an image for the optics unit. SALT stands for : (S)ize, (A)ttitude, (L)ocation and (T)ype. Feb 20 5:43 PM Try these : 1. Use the first law of reflection to locate the image of the arrow as viewed through the plane mirror. Feb 21 12:48 PM 6
Hint : Draw intersecting rays of light at the top and bottom of the arrow and draw in the reflected rays. Trace these rays back into the mirror and see where they meet. Feb 21 12:51 PM 2. Prove that you don't need a full length mirror to see an image of your whole body. Feb 21 12:54 PM 7
Optics 4 Plane Mirror Reflection.notebook How can mirrors get rid of pain? What is this guy doing? Feb 23 7:05 PM What was that???... it's called a "mirror box" and it's used to treat "phantom pain" in amputees. ("phantom pain" is pain felt after a limb has been amputated it's VERY hard to get rid of, but this is a relatively new treatment for it) MIRRORS AT WORK! Feb 23 7:07 PM 8
Optical illusions: Pepper's ghost Feb 23 7:10 PM Locating an image in a plane mirror Images of objects appear to be the same distance behind the mirror as the object is in front (as directed along the normal) Feb 20 5:49 PM 9
Image characteristics for a plane mirror For a plane mirror we have : size same as object attitude right side up / erect location same distance behind the mirror as object is in front type behind the surface of the mirror so virtual Feb 21 12:47 PM Feb 21 12:55 PM 10