Write down each definition and match Write down each definition and match it with the correct term.it with the correct term.

1.1. A picture of an object formed by A picture of an object formed by light rayslight rays

2.2. The point where parallel light rays The point where parallel light rays striking a concave mirror meetstriking a concave mirror meet

3.3. A surface that curves out like the A surface that curves out like the back of a spoon.back of a spoon.

Terms: concave, convex, focal point, Terms: concave, convex, focal point, optics, imageoptics, image

Possible matching answersPossible 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 Lenses form images by refracting lightrefracting light

A medium can refract lightA 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 RainbowsRefraction and Rainbows• Rainbows are cause by Rainbows are cause by

refraction and reflection of refraction and reflection of light through spherical water light through spherical water drops which act as prisms.drops which act as prisms.– Like a prism, water drops Like a prism, water drops

separate the wavelengths of separate the wavelengths of sunlight to produce a spectrum.sunlight to produce a spectrum.

– Unlike a prism, only one color Unlike a prism, only one color reaches your eye from each reaches your eye from each drop.drop.

• Red appears at the top of a Red appears at the top of a rainbow because it is coming rainbow because it is coming from higher dropsfrom higher drops

• Violet comes from lower dropsViolet comes from lower drops

Shape determines how Shape determines how lenses form imageslenses form images

• Flat mediums- produce a clear image Flat mediums- produce a clear image on other sideon other side

• A lens is a clear optical tool that A lens is a clear optical tool that refracts light- non flat mediums.refracts light- non flat mediums.– Different lenses refract light in different Different lenses refract light in different

waysways– These different images formed are useful These different images formed are useful

for a variety of purposesfor 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 LensConcave 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 lensesImages 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 How Convex Lenses Form ImagesImages

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

Convex LensesBigger? 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 LensesConcave Lenses

• Always right side up and smaller than normal appearance.

• Distance between lens and object does not make a difference.