* Light is the range of frequencies of electromagnetic waves that stimulate the retina of the eye. Light waves have wavelengths from about 400 nm (4.0 x m) to 700 nm (7.0 x m). The shortest wavelengths are seen as violet light. As the wavelength increases, the colors change to blue, green, yellow, orange, and finally red.

Facts about Light It is a form of Electromagnetic Energy It is a part of the Electromagnetic Spectrum and the only part we can really see

Facts about Light The speed of light, c, is constant in a vacuum. Light can be: REFLECTED ABSORBED REFRACTED EMITTED Light is an electromagnetic wave in that it has wave like properties which can be influenced by electric and magnetic fields.

A nanometer is a very, very small distance. It is equal to one billionth of a meter. 1 Nanometer = 1x10 -9 meters When converting from nanometers to meters you simply multiply by 1x10 -9 meters. Example: How many meters are in 700 nm? When converting from meters to nanometers you divide by 1x10 -9 m. Example: How many nanometers are in 4.0 x m? 700 nm x (1x10 -9 ) = 700 x or properly written as 7.0 x m 4.0x10 -7 m / 1.0x10 -9 = 4.0 x 10 2 or 400 nm

What is the frequency of yellow light? (wavelength = 556 nm) Known λ = 556 nm c = 3.0 x 10 8 m/s Unknown Frequency (f)c = λ f Equation 3.0 x 10 8 m/s = 5.56 x m (f) f = 3.0 x 10 8 m/s 5.56 x m = 5.4 x Hz

A luminous body emits light waves. The sun is a luminous body. Name some other examples of luminous bodies Light Bulb Lit Candle Stars Camp fire

An illuminated body reflects light waves. The moon and earth are examples of illuminated bodies. Name some other illuminated bodies: Planets People Any object that reflects light

Materials are said to be transparent if you can see objects through them. Transparent objects allow light to pass through them (they transmit light). Materials are translucent if they transmit light, but objects cannot be seen clearly through them. Examples would be lamp shades, frosted glass, etc. Opaque materials do not transmit light.

Our eyes detect only a part of the electromagnetic spectrum. The part of the spectrum that our eyes detect is called “visible or white light”. White light is composed of colors. Each color in the visible spectrum is associated with a specific wavelength of light.

Primary Colors Red Green Blue Secondary Colors Magenta Yellow Cyan The primary colors of light (red, green, and blue) are called “primary” because when all 3 are added together they produce white light. The secondary colors of light (magenta, yellow, and cyan) are called “secondary” because they are the result of the combination of any two primary light colors.

The additive process is the process of combining two or more primary light colors to get various secondary colors of light. By adjusting the intensities of the primary colors, you can achieve any shade of color.

Determine the color of a white sheet of paper when the following combinations of light are shown onto it. Answers:______________________ ____________ Yellow Magenta Cyan

We see only the colors of light that enter our eye. Pigments are molecules that absorb certain wavelengths of light. Any wavelength of light that is not absorbed by a pigment is then reflected. It is the reflected light that enters our eye. This is called the subtractive process of color formation. Appears ??????

Answers:____________________________ Magenta Cyan

You are an artist. You only have the following colors of paint (pigments) to use when painting the bird below (magenta, cyan, yellow). Describe what you did in order to achieve the painting below.

Light waves are produced by vibrating electric charges. Light is a transverse wave which has both an electric and a magnetic component.

Light waves are naturally unpolarized (they exist in more than one plane). However filters can be used to “polarize” light. Light is sent through a filter which absorbs the light that is traveling perpendicular to the polarization axis. The light that was traveling parallel to the axis is transmitted.

3-D movies use polarization to give the them their special effects. This is done by two movie projectors, each showing the same movie but with oppositely polarized light. You then place polarizing glasses on so that each eye sees a different polarization of light.

The sky appears blue because nitrogen and oxygen molecules have a tendency to absorb and reemit blue, indigo, and violet light (light scattering). Our eyes, being more sensitive to blue light, see the sky as being blue. The sun appears yellow because the other two primary colors of light (red and green) are not scattered by the atmosphere. Remember red + green = yellow.

As the sun sets, the rays from the Sun have to travel through more of the earth’s atmosphere before we see them. The increased distance traveled through the atmosphere causes more scattering of longer wavelength light which gives the sky its orange/yellow tint.

The Law of “REFLECTION” The Law of Reflection states that- " the angle of incidence (incoming ray) equals the angle of reflection (outgoing ray)" The angles are measured from a perpendicular line to the surface called a NORMAL. NORMAL

The Line of Sight Without light, there would be no sight An object has to be LUMINOUS or ILLUMINATED in order to be seen In order to view an object, you must sight along a line at that object; and when you do light will come from that object to your eye along the line of sight.  To view the image of an object in a mirror, you must sight along a line at the image. One of the many rays of light from the object will approach the mirror and reflect (according to the law of reflection) along your line of sight to your eye.

3 types of mirrors Concave Convex Plane

m/mmedia/optics/ifpm.gif Image Formation for Plane Mirrors

Plane Mirror Suppose we had a flat, plane mirror mounted vertically. A candle is placed 10 cm in front of the mirror. WHERE IS THE IMAGE OF THE CANDLE LOCATED? mirror Object Distance, D o = 10 cm Same side as the object? On the surface of the mirror? Behind the mirror?

Plane Mirror Suppose we had a flat, plane mirror mounted vertically. A candle is placed 10 cm in front of the mirror. WHERE IS THE IMAGE OF THE CANDLE LOCATED? mirror Object Distance, D o = 10 cmImage Distance, D i = 10 cm D o =D i & the heights are equal as well Virtual Image Conclusion: With plane mirrors, the object distance ( in front of mirror ) will equal the image distance ( behind mirror ). Object and image are the same height.

Plane Mirror Virtual Images are basically images which cannot be visually projected on a screen (they form on opposite side of mirror from object) If this box gave off light, we could project an image of this box on to a screen provided the screen was on the SAME SIDE as the box. ( Virtual images are images that are formed in locations where light does not actually reach). CONCLUSION: VIRTUAL IMAGES are ALWAYS on the OPPOSITE side of the mirror relative to the object.

Plane Mirror Characteristics of a plane mirror image:  Do = Di  Image height = object height  Always forms a virtual image (image on opposite side of mirror from object)  Left-right reversal

Spherical Mirrors – Convex & Concave Also called CONVERGING mirror Also called DIVERGING mirror

Converging (Concave) Mirror A converging mirror is one that is spherical in nature by which it can FOCUS parallel light rays to a point directly in front of its surface. Every spherical mirror can do this and this special point is at a “fixed” position for every mirror. We call this point the FOCAL POINT. To find this point you MUST use light from “infinity” Light from an “infinite” distance, most likely the sun.

Converging (Concave) Mirror Since the mirror is spherical it technically has a CENTER OF CURVATURE, C. The focal point happens to be HALF this distance. We also draw a line through the center of the mirror and call it the PRINCIPAL AXIS.

Ray Diagram A ray diagram is a pictorial representation of how the light travels to form an image and can tell you the characteristics of the image. Principal axis f C object Rule One: Draw a ray, starting from the top of the object, parallel to the principal axis and then through “f” after reflection.

Ray Diagram Principal axis f C object Rule Two: Draw a ray, starting from the top of the object, through the focal point, then parallel to the principal axis after reflection.

Ray Diagram Principal axis f C object Rule Three: Draw a ray, starting from the top of the object, through C, then back upon itself. What do you notice about the three lines? THEY INTERSECT The intersection is the location of the image ( the top of the arrow head ).

Ray Diagram – Image Characteristics Principal axis f C object After getting the intersection, draw an arrow down from the principal axis to the point of intersection. Then ask yourself these questions: 1)Is the image on the SAME or OPPOSITE side of the mirror as the object? Same, therefore it is a REAL IMAGE. 2)Is the image ENLARGED or REDUCED? Reduced 3) Is the image INVERTED or RIGHT SIDE UP? Inverted

Real Image Real Images are ones you can project on to a screen. For MIRRORS they always appear on the SAME SIDE of the mirror as the object. object image The characteristics of the image, however, may be different from the original object. These characteristics are: SIZE (reduced,enlarged,same size) POSITION (same side, opposite side) ORIENTATION (right side up, inverted)

Watch this Cool demo of a Concave Mirror yer_embedded&v=KVpSCICCD9Ahttp:// yer_embedded&v=KVpSCICCD9A

Concave Mirror Scenarios Case 4: The object is located at F Case 1: The object is located beyond C Case 2: The object is located at C Case 3: The object is located between C and F Case 5: The object is located in front of F

Diverging (Convex) Mirror A convex mirror is sometimes referred to as a diverging mirror due to the fact that incident light originating from the same point (on an object) will reflect off the mirror surface and diverge. Being that the reflected (red) rays of light do not intersect on the object side, you must extend the tail end of the reflected (red) rays beyond the mirror surface. The image will form beyond the mirror where all of those extended rays intersect.

Ray Diagram 1. Pick a point on the top of the object and draw two incident rays traveling towards the mirror. 2. Once these incident rays strike the mirror, reflect them according to the law of reflection. 3. Locate and mark the image of the top of the object. 4. Repeat the process for the bottom of the object.

Convex Mirror Scenarios The diagrams above show that in each case, the image is: 1) located behind the convex mirror (a virtual image) 2) an upright image 3) reduced in size (i.e., smaller than the object)  As object gets closer to mirror, image gets closer and bigger Object Image

The Mirror/Lens Equation Is there any OTHER way to predict image characteristics besides the ray diagram? YES! One way is to use the MIRROR/LENS equation to CALCULATE the position of the image.

Mirror/Lens Equation Assume that a certain concave spherical mirror has a focal length of 10.0 cm. Locate the image for an object distance of 25 cm and describe the image’s characteristics cm What does this tell us? First we know the image is BETWEEN “C” & “f”. Since the image distance is POSITIVE the image is a REAL IMAGE. Real image = positive image distance Virtual image = negative image distance What about the size and orientation?

Magnification Equation To calculate the orientation and size of the image we use the MAGNIFICATION EQUATION. Here is how this works: If we get a POSITIVE magnification, the image is UPRIGHT. If we get a NEGATIVE magnification, the image is INVERTED If the magnification value is GREATER than 1, the image is ENLARGED. If the magnification value is LESS than 1, the image is REDUCED. If the magnification value is EQUAL to 1, the image is the SAME SIZE as the object. Using our previous data we see that our image was INVERTED, and REDUCED.

Example Assume that a certain concave spherical mirror has a focal length of 10.0 cm. Locate the image for an object distance of 5 cm and describe the image’s characteristics. -10 cm 2x VIRTUAL (opposite side) (negative d i ) Enlarged (M is bigger than 1) Upright (M is positive) Characteristics?