Optical Systems Make use of Mirrors and Lenses!

 Sir Isaac Newton – developed the particle model of light- thought that light was made of tiny particles that travelled in a straight line until they entered the eye. Light is made up of both the particle model and the wave model = the ray model of light. Light is represented as a straight line showing direction of travel

 What you see depends on the amount of light available  In dim light you can no longer tell colours apart  The type of matter in an object determines the amount of light it absorbs, reflects, and transmits

Light can pass through freely, only a small amount  of light is absorbed and reflected  (Example: air, water, and glass)

Most light rays get through but they are scattered in all directions (Example: frosted glass)

Prevents light from passing through (Example: cardboard)

 You can predict shadows using the ray model of light  Size of shadows are related to distance from the light source

To act like a mirror a material must: have a smooth surface compared to the wavelength of the light striking the surface If the surface is uneven then the rays will be reflected at different angles

Incoming ray = incident ray Ray that bounces off = reflected ray Right angle between the two rays Normal line is at right angles to the reflecting surface Angle of incidence (i) = Angle of reflection (r) = Law of Reflection

 When light is bent, when it changes speed from one medium into another, it is called refraction When light moves between air and glass it slows down because glass is more dense Angle of refraction = angle of a ray of light emerging from the boundary between two materials it is measured between the normal and the refracted ray

 Can occur when light passes through air of different temperatures  Warm air is less dense than cold air  Results in a mirage

Textbook questions Page 181 Questions # 1-7, 9 There will be a homework check!

 Plane mirror – flat smooth mirror, where you appear to be the same distance behind the mirror as you are in front of the mirror

The reflected light that bounces off the mirror is doing so in all directions but only certain ones reach the pupil of our eye Our brain knows that light travels in a straight line so it interprets the image coming from behind the mirror

plane mirror  Both will be the same when using a plane mirror  A plane mirror will produce an image that has the same orientation as the object (both upright) but left and right will appear reversed

Curve inwards, and reflect light rays to form images Causes light rays to converge and meet at a focal point Image produced depends on the distance form the focal point

Image will be small and upside down as you get closer the image will get larger to a point where it is between the mirror and the focal point where the image will appear upright (see p.185) Used for flashlights, headlights, lighthouses, telescopes, and make-up mirrors

Curves outward, opposite to concave, diverging rays are given off Image is always upright and smaller then the actual image

Main Characteristics: 1. Objects appear to be smaller than they are 2. More objects can be seen than in a plane mirror of the same size Used for security mirrors, on car mirrors

 Textbook questions  Page 189  Questions #1-5

Lens = a curved piece of transparent material that refracts light rays to either diverge or converge Can be either convex or concave

Are thinner in the middle than the edge Makes light rays diverge and won’t meet at a focal point Image is always upright and smaller than the actual object Uses: glasses, telescopes

 Thicker in the middle  Light rays converge meeting at a focal point behind the lens  Image depends on the distance between the lens and the object  Uses: magnifying glasses, cameras, telescopes, microscopes, our eye

Focal length = distance between the lens/mirror and the focal point This has been mathematically determined for distance of object

Distance of Object from Lens  More than 2 focal lengths  Between 1 and 2 focal lengths  Object at focal length  Less than 1 focal length Type of Image Formed  Smaller, inverted  Larger, inverted  No image  Larger, upright

Textbook Questions Page 197 Questions # 2-7, 11