• 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

11.1

medium

electromagnetic

waves

radiation

visible light

electromagnetic

spectrum

visible spectrum

CHARACTERISTICS OF LIGHT

• There are several ways to produce light. Each method involves

the conversion of another type of energy into light energy.

11.2

incandescence

electric discharge

phosphorescence

fluorescence

chemiluminescence

bioluminescence

triboluminescence

METHODS FOR PRODUCING LIGHT

Method How Light is Produced Example

incandescence An object is heated to a high

temperature

molten glass that glows

electric discharge An electric current passes

through a gas

lightening

phosphorescence A special material absorbs

UV light and releases visible

light over a period of time

glow-in-the-dark stickers

fluorescence A material absorbs UV light

and immediately releases

visible light

fluorescent light

chemiluminescence A chemical reaction

produces light directly

light stick

bioluminescence An organism releases light

through a chemical reaction

in its body

firefly

triboluminescence Certain crystals are

scratched, crushed, or

rubbed

biting a wintergreen candy

• 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

THE LASER – A SPECIAL TYPE

OF LIGHT

11.3

• 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.

– Opaque objects either absorb or reflect all incident light.

• Light rays are used to illustrate the path of light when it

strikes an object.

11.4

transparent

incident light

translucent

opaque

light rays

incident ray

reflected ray

mirror

HOW LIGHT BEHAVES WHEN

IT STRIKES OBJECTS

incident

ray

reflected

ray

mirror

• 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.

– The angle of incidence equals

the angle of reflection.

– The incident ray, the reflected

ray, and the normal all lie

in the same plane.

11.4 PROPERTIES OF PLANE MIRRORS

plane

normal

perpendicular

angle of incidence

angle of reflection

• 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.

– The incident ray, the reflected ray, and the normal all lie

in the same plane

11.6

image

virtual image

real image

THE LAWS OF REFLECTION

• 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).

• The image in a plane mirror is the same size as the

object, upright, behind the mirror, and virtual.

11.7

image

virtual image

real image

IMAGE CHARACTERISTICS

IN PLANE MIRRORS

• 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.

11.7 HOW TO LOCATE THE IMAGE

IN A PLANE MIRROR

• 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).

– A convex mirror causes parallel light rays to diverge, or spread apart.

11.9 PROPERTIES OF CURVED MIRRORS

concave

(converging)mirror

principal axis

converge

focus

centre of curvature

vertex

convex (diverging)

mirror

diverge

principal axis

centre of

curvature

vertex

• There are four imaging rules that you can use to locate the image of an object

in a converging mirror.

11.9 HOW TO LOCATE THE IMAGE IN A

CONVERGING (CONCAVE) MIRROR

A light ray through the centre of curvature is reflected back

onto itself.

A light ray parallel to the principal axis is reflected through

the focus. This is how the focus is defined.

A ray through F will reflect parallel to the principal axis.

A ray aimed at the vertex will follow the law of reflection.

• 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.

11.9 IMAGE CHARACTERISTICS IN

CONVERGING MIRRORS

• There are three imaging rules that you can use to locate the image of an object

in a diverging mirror.

11.9 HOW TO LOCATE THE IMAGE IN

A DIVERGING (CONVEX) MIRROR

• 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)

11.9 IMAGE CHARACTERISTICS IN

DIVERGING MIRRORS