Transcript File
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 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