A Brief Look at LIGHT

Light usually travels only in a straight line. This is known as the ... Law of Rectilinear Propagation

Diagrams with Light are referred to as ray diagrams where a ray is a single path followed by light and a beam is a ‘bundle’ of light rays.

When light strikes matter It can be affected in 3 different ways: Transmitted: light passes through a medium Ex. Windows Reflected: light bounces off an object Ex. Mirrors Absorbed: light disappears (or certain wavelengths) Green object  all wavelengths of light except green are absorbed

Classifying Objects Objects may be classified based on how well they transmit light: Transparent: transmits ALL light Opaque : transmits NO light Translucent: transmits SOME light

The Reflection of Light Regular Reflection: this is reflection of light from smooth shiny surfaces.

Laws of Reflection Normal Incident Ray Angle of Incidence Angle of Reflection Reflected Ray 90o Mirror Point of incidence

Laws of Reflection First Law: The angle of incidence is equal to the angle of reflection Normal Incident Ray Angle of Incidence Angle of Reflection Reflected Ray Mirror

Laws of Reflection Laws of Reflection Second Law: The incident ray, reflected ray, and normal all lie on the same plane Normal Incident Ray Angle of Incidence Angle of Reflection Reflected Ray Mirror

Diffuse Reflection Many surfaces appear to be smooth, however when they are viewed under a microscope it is clear they are not. Because of the uneven surface, the light rays are scattered in many directions (diffused).

Diffuse Reflection Further examination of a irregular surface show that they too obey the laws of reflection (ie. Angle of incidence = angle of reflection).

Diffuse Reflection Most objects are made of rough surfaces (and therefore scatter light); if this did not happen, indoor lighting would not be effective. ie. Walls, floors, ceilings, etc. scatter light in all directions, making them visible.

Time to practice! Complete the worksheet “kinds of reflections” Complete the worksheet “regular and diffuse reflection” Read text p.479-481 and p.484-486 Do Questions: p. 481 #3, 5, p. 486 #1-5

Optical Images An image is the representation of an object formed by the interaction of light rays. Characteristics (LOST): Location: behind or in front of mirror Orientation: vertical (upright or inverted) lateral (left to right) Size: bigger, smaller or same size as object Type : Real – when the reflected rays converge in front of the mirror to produce an image (can be seen on a screen) or Virtual – when the reflected rays converge behind the mirror (cannot be reflected onto a screen)

Images Formed in Plane Mirrors How do I see an image of the arrow??

Images Formed in Plane Mirrors Light from the arrow hits the mirror

Images Formed in Plane Mirrors ..and is reflected into my eye

Images Formed in Plane Mirrors The image!! ..and my brain ‘sees’ the image where the light appears to have come from!

Characteristics of a PLANE MIRROR Image Characteristics in a plane mirror are always: Location: behind the mirror the same distance from the mirror as the object Orientation: image is upright, and laterally inverted Size: same size as object Type : virtual (In you book it’s SALT (Size, Attitude, Location, Type))

Homework Time! Complete Worksheet “Plane Mirrors and their Images” Complete Worksheet “Drawing Images in a Plane Mirror” Read pg. 488-492 Do Questions pg. 493 #1-7, 9 REMINDER: QUIZ on Tuesday!!! (electromagnetic spectrum, sources of light, law of reflection and images in a plane mirror)