2 Light We see objects because of reflected light Travels far and fast (3 x 108 m/s)Travels in a straight lines, called rays
3 Reflection Review Law of reflection: θi = θr Light rays bounce off a mirror at the same angle at which they arriveWe always define angles relative to the normal (the line perpendicular to the mirror (or lens)
4 Types of Mirrors Plane Mirror – Concave Mirror – Convex Mirror – A flat mirror that reflects light in a regular wayConcave Mirror –Reflects light from inner surfaceLight rays are reflected so that they “come together” at a point; a converging mirrorConvex Mirror –Reflects light from outer surfaceLight rays are reflected so that they “go apart” and never come to a point; a diverging mirror
5 Object vs. Image Object – the source of light rays Ex: you when you look in the bathroom mirrorImage – reproduction of object formed with lenses or mirrors.The image is formed at the intersect of the reflected rays.
6 Kinds of Images Real images Formed by converging light rays Can be projected on a screenInverted orientationVirtual imagesFormed by diverging light raysCannot be seen on a screenErect orientation
8 Reflection & MirrorsA mirror reflects rays of light so that they change their pathMirrors can create a virtual imageImage appears behind the mirror and is reversedThe light rays are reflected back to your eye at an equal but opposite anglesIncident ray – the ray that comes from the object and hits the mirrorReflected ray – the ray that bounces off the mirror
9 Objects, Images & Plane Mirrors Plane mirror – flat, smooth surface that reflects light in a regular wayEx: your bathroom mirrorObjectImage
10 Things to know about Plane Mirrors Object size = Image sizeObject distance = Image distanceOrientation = UprightForms a virtual imageImage is reversed (left to right)
11 Drawing Ray Diagrams – Plane A ray striking perpendicular to the surface (parallel to normal) will reflect perpendicular to the surface; the reflected ray is extended behind the mirrorA ray striking at any angle will reflect so that θi = θr; the reflected ray is extended behind the mirror to form the image
13 Refraction & LensesA lens uses refraction to cause light to come together or spread apartRefraction – The bending of light as a result of light crossing a boundary between two different mediaEX. Glass, Plastic, WaterLens – a transparent optical device that is used to converge or diverge light rays (bend light)
14 Lens TypesConvex Lens (converging lens) – bend parallel light rays passing through them inward toward the focal pointThicker in the center than the edgesLight travels slower in the thick centerFocal length (f) is always positive
15 Things to know about Convex lenses… If the object is outside the focal point, it is real & invertedIf the object is at AT the focal point, no image is formedIf the object is inside the focal point, the image is upright & virtual.Let’s take a look…
17 Conventions to Know: Focal Length Object Distance: Image Distance f is positive for convex lensesObject Distance:do is positive for REAL objectsdo is negative for a virtual object*Image Distancedi is positive for a real image (image on other side of lens)di is negative for a virtual image (image on the same side of the lens)
18 Example 1An object is placed 35 cm from a convex lens with a focal length of 20 cm.How far is the image from the lens?What type of image is formed?
19 Example 2A virtual image is formed 20 cm from a convex lens having a focal length of 20 cm.How far is the object from the lens?What is the orientation of the image?
20 Drawing Ray Diagrams - Lenses Incident light rays parallel to the principal axis of a lens are refracted through the focal point (F)* (ray 1)Incident rays that pass through the secondary focal point (F’) are refracted parallel to the principal axis (ray 2)Incident rays passing through the center of lens are not refracted (ray 3)