# 10 2 Properties of Light and Reflection Reflection

• Slides: 28

10. 2 Properties of Light and Reflection

Reflection

Reflection - the change in direction of a light ray when it bounces off a surface

Rays of Light § Light travels in a straight line (as long as it’s moving § § through the same medium) § Medium – the substance through which light travels Ray-a straight line with an arrowhead that shows the direction in which light waves are travelling. Ray diagrams - can be used to make predictions about appearance of objects

Ray Model of Light § Ray – A single unit of light §Represented by 1 arrow § Beam – A bundle of light rays travelling in one direction §Represented by many arrows

Definitions You Need to Know § incident ray – a ray of light that travels from a light § § § source towards a surface angle of incidence – angle between the incident ray and the normal in a ray diagram normal - a line that is perpendicular to a surface where a ray of light meets the surface reflected ray – a ray that begins at the point where the incident ray and the normal meet angle of reflection – the angle between the reflected ray and the normal in a ray diagram plane mirror – a mirror with a flat reflective surface

Laws of Reflection 1. The incident ray, the reflected ray, and the normal always lie on the same plane. 2. The angle of reflection is equal to the angle of incidence. r= i Law of reflection states that the angle of incidence equals the angle of reflection

Drawing Ray Diagrams Normal – dotted line perpendicular to the surface (90◦ angle)

Ray Diagrams

Protractor § http: //www. amblesideprimary. com/ambleweb/ mentalmaths/protractor. html § LET’S PRACTICE USING A PROTRACTOR

Images in Plane Mirrors § Plane Mirror – A mirror with a flat, reflective surface § Scientists call an object in front of a mirror the § object, and they call what is seen in the mirror the image of the object. Using the laws of reflection to rays going from the object, you can predict where the image will be and where the image would look like.

Virtual Image § Virtual Image- an image formed by rays that appear to § be coming from a certain position, but are not actually coming from this position image does not form a visible projection on a screen § brain assumes that a light § ray travels in a straight line note the lateral inversion all images in plane mirrors are reversed

Let’s use the power of Reflection on Abraham Lincoln’s face

Abraham Lincoln Left side face

Abraham Lincoln “Left side” face “Right side” face

Four Characteristics of an Image L. O. S. T 1. Location § closer than, farther than, or the same distance as the object to the mirror 2. Orientation § upright or inverted 3. Size § same size, larger than, or smaller than the object 4. Type § real or virtual image

Characteristics of an Image in a Plane Mirror 1. Location § the same distance as the object to the mirror 2. Orientation § upright 3. Size § same size 4. Type § virtual image § You can predict these characteristics by drawing a ray diagram

Location § Image is located on the same side of the § § mirror Image is located on the opposite side of the mirror Image can also be located at a specific point (e. g. at centre of curvature, f<di<2 f, etc. ) § Note: image location will always be di=do for plane mirrors

Orientation a) Upright - image is right-side up b) Inverted - image is upside-down c) Laterally Inverted - image is flipped horizontally a) b) c)

Size a) Enlarged - image is larger than the object b) Reduced - image is smaller than the object c) Same - image is the same size as the object a) b) c)

Type § Real - image appears in front of the mirror (could be projected onto a screen) § Virtual - image appears behind the mirror

Locating an Image in a Plane Mirror Using a Ray Diagram Page 416

Locating an Image in a Plane Mirror Using a Ray Diagram

Locating an Image in a Plane Mirror Using a Ray Diagram

Locating an Image in a Plane Mirror Using a Ray Diagram

Locating an Image in a Plane Mirror Using a Ray Diagram

Reflection and Stealth Technology The shape of and surface paint on the stealth aircraft absorbs and reflects radar waves so that only a few of the waves reach the ground radar station. This renders the aircraft virtually invisible.

Homework § Read Section 10. 2 on Pages 411 -416 § Complete # 1 -4, 6 found on Page 418.