Write down each definition and match it with the correct term. 1.A picture of an object formed by light rays 2.The point where parallel light rays striking a concave mirror meet 3.A surface that curves out like the back of a spoon. Terms: concave, convex, focal point, optics, image

Possible matching answers 1.A picture of an object formed by light rays IMAGE 2.The point where parallel light rays striking a concave mirror meet FOCAL POINT 3.A surface that curves out like the back of a spoon. CONVEX

Lenses form images by refracting light

A medium can refract light Refract: the bending of a wave as it crosses the boundary between two mediums at an angle other than 90 degrees. –Mediums: air  lens  air –Occurs because one side of the light wave reaches the new medium (lens) slightly before the other side does. –That side changes speed, while the other continues at regular speed, causing it to turn.

Direction in which a light wave turns depends on whether the new medium slows the wave down or allows it to travel faster. –Denser medium-slow down –Thinner medium-speed up The normal- imaginary line perpendicular to the new surface that helps describe refraction –If the medium slows the wave, the wave will turn toward the normal. –If the medium lets the wave speed up, the wave will turn away from the normal. Refraction of light

Refraction and Rainbows Rainbows are cause by refraction and reflection of light through spherical water drops which act as prisms.Rainbows are cause by refraction and reflection of light through spherical water drops which act as prisms. –Like a prism, water drops separate the wavelengths of sunlight to produce a spectrum. –Unlike a prism, only one color reaches your eye from each drop. Red appears at the top of a rainbow because it is coming from higher dropsRed appears at the top of a rainbow because it is coming from higher drops Violet comes from lower dropsViolet comes from lower drops

Shape determines how lenses form images Flat mediums- produce a clear image on other sideFlat mediums- produce a clear image on other side A lens is a clear optical tool that refracts light- non flat mediums.A lens is a clear optical tool that refracts light- non flat mediums. –Different lenses refract light in different ways –These different images formed are useful for a variety of purposes Types of lenses: convex and concaveTypes of lenses: convex and concave

Convex Lens Curved outward Parallel light rays passing through a convex lens are refracted inward. –They meet at a focal point on the other side of the lens –Rays refract twice: when entering the new medium and when leaving the new medium. –Rays on the outer part of the lens are refracted the most –Rays on the principal axis-the line joining the center of the two curved lenses- will go straight through and not refract. principal axis focal point

Concave Lens The lens is curved inward. Parallel light rays that pass through a concave lens are refracted outward. –Rays do not ever meet. –Rays refract twice: when entering the new medium and when leaving the new medium. –Rays on the outer part of the lens are refracted the most –Rays on the principal axis-the line joining the center of the two curved lenses- will go straight through and not refract. Principle Axis

Images formed by lenses Type of image depends on –Lens type –For convex lenses: the distance between the lens and the object. Convex lens: Distance from lens is measured in focal length- the distance from the center of the lens to the lens’s focal point.

How Convex Lenses Form Images Look at the 3 steps below to see how an image is formed by a convex lens. Step 1 is repeated from the previous slide.Look at the 3 steps below to see how an image is formed by a convex lens. Step 1 is repeated from the previous slide.

Convex Lenses Bigger? Smaller? Flip-Flop? If the image is more than two focal lengths away, the image will be upside down and smaller. If the image is between 1 and 2 focal lengths away the image will be upside down and larger. If an object is less than one focal length away it will appear right side up and larger.

Concave Lenses Always right side up and smaller than normal appearance. Distance between lens and object does not make a difference.