11.1 CHARACTERISTICS OF LIGHT

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As wavelength decreases, energy increases. VISIBLE LIGHT Visible light is one small part of the electromagnetic spectrum.

1 CHARACTERISTICS OF LIGHT 11.1 An electromagnetic wave has both electric and magnetic parts; it does not require a medium, and it travels at the speed of light. As wavelength decreases, energy increases. VISIBLE LIGHT Visible light is one small part of the electromagnetic spectrum. Visible light is made up of seven different colours of light: red, orange, yellow, green, blue, indigo, and violet. Each colour in the visible spectrum has a different amount of energy. Examples??? See page 466 in textbook medium electromagnetic waves radiation visible light electromagnetic spectrum visible spectrum

2 METHODS FOR PRODUCING LIGHT There are several ways to produce light. Each method involves the conversion of another type of energy into light energy. Method How Light is Produced Example incandescence An object is heated to a high molten glass that glows temperature electric discharge An electric current passes lightening through a gas phosphorescence A special material absorbs UV light and releases visible light over a period of time glow-in-the-dark stickers fluorescence chemiluminescence bioluminescence triboluminescence A material absorbs UV light and immediately releases visible light A chemical reaction produces light directly An organism releases light through a chemical reaction in its body Certain crystals are scratched, crushed, or rubbed fluorescent light light stick firefly biting a wintergreen candy 11.2 incandescence electric discharge phosphorescence fluorescence chemiluminescence bioluminescence triboluminescence

3 THE LASER A SPECIAL TYPE OF LIGHT 11.3 Light from a laser has special properties. A laser produces electromagnetic waves of exactly the same energy level This results in visible light being of a very pure colour A red laser light entering a triangular prism will still look red on exit Laser light is also very intense because the electromagnetic waves travel in the same direction and are exactly in unison Never look directly at a laser beam

4 HOW LIGHT BEHAVES WHEN IT STRIKES OBJECTS 11.4 When light strikes an object, it is reflected, transmitted, or absorbed, depending on the object. Transparent objects transmit all or almost all incident light. Translucent objects transmit some incident light, and either absorb or reflect the rest. transparent incident light translucent opaque light rays incident ray reflected ray mirror Opaque objects either absorb or reflect all incident light. Light rays are used to illustrate the path of light when it strikes an object. incident ray reflected ray mirror

PROPERTIES OF PLANE MIRRORS 11.4 To understand what happens when light strikes a plane mirror, you must draw a normal to the mirror at the point where the incident ray strikes the mirror.

5 PROPERTIES OF PLANE MIRRORS 11.4 To understand what happens when light strikes a plane mirror, you must draw a normal to the mirror at the point where the incident ray strikes the mirror. The normal must be perpendicular to the mirror. There are two predictable results when light strikes a plane mirror. plane normal perpendicular angle of incidence angle of reflection The angle of incidence equals the angle of reflection. The incident ray, the reflected ray, and the normal all lie in the same plane.

6 THE LAWS OF REFLECTION 11.6 Specular reflection VS diffuse reflection. The incident ray and the reflected ray behave in predictable ways, which leads to the two laws of reflection. The angle of incidence equals the angle of reflection. image virtual image real image The incident ray, the reflected ray, and the normal all lie in the same plane

7 IMAGE CHARACTERISTICS IN PLANE MIRRORS 11.7 When you look into a plane mirror, you see an image that has certain characteristics. The characteristics can be described in terms of size, attitude (which way the image is oriented), location, and type (whether or not light actually arrives at the image location). image virtual image real image The image in a plane mirror is the same size as the object, upright, behind the mirror, and virtual.

8 HOW TO LOCATE THE IMAGE IN A PLANE MIRROR 11.7 There are two methods that you can use to locate the image of an object in a plane mirror. Use light rays. Use equal perpendicular lines.

9 PROPERTIES OF CURVED MIRRORS 11.9 A curved mirror can be formed from part of a sphere. There are two general types of curved mirrors. A concave mirror causes light rays that are parallel to the principal axis to converge, or meet, at one point (the focus). concave (converging)mirror principal axis converge focus centre of curvature vertex convex (diverging) mirror diverge principal axis centre of curvature vertex A convex mirror causes parallel light rays to diverge, or spread apart.

HOW TO LOCATE THE IMAGE IN A CONVERGING (CONCAVE) MIRROR 11.9 There are four imaging rules that you can use to locate the image of an object in a converging mirror.

10 HOW TO LOCATE THE IMAGE IN A CONVERGING (CONCAVE) MIRROR 11.9 There are four imaging rules that you can use to locate the image of an object in a converging mirror. A light ray parallel to the principal axis is reflected through the focus. This is how the focus is defined. A light ray through the centre of curvature is reflected back onto itself. A ray through F will reflect parallel to the principal axis. A ray aimed at the vertex will follow the law of reflection.

11 IMAGE CHARACTERISTICS IN CONVERGING MIRRORS 11.9 Images in converging mirrors can be described using the same characteristics as with plane mirrors: size, attitude, location, and type. The image characteristics change, depending on where the object is located relative to the mirror.

12 HOW TO LOCATE THE IMAGE IN A DIVERGING (CONVEX) MIRROR 11.9 There are three imaging rules that you can use to locate the image of an object in a diverging mirror.

IMAGE CHARACTERISTICS IN DIVERGING MIRRORS 11.9 Images in diverging mirrors can be described using the same characteristics as with converging mirrors: size, attitude, location, and type.

13 IMAGE CHARACTERISTICS IN DIVERGING MIRRORS 11.9 Images in diverging mirrors can be described using the same characteristics as with converging mirrors: size, attitude, location, and type. The image characteristics are always the same, no matter where the object is located relative to the mirror. The image is smaller, upright, behind the mirror, and virtual. Applications of concave and convex mirrors??? (flashlight see page 498)

SNC 2PI Optics Unit Review /95 Name:

SNC 2PI Optics Unit Review /95 Name: Part 1: True or False Indicate in the space provided if the statement is true (T) or false(f) [15] 1. Light is a form of energy 2. Shadows are proof that light travels