Chapter 5
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Chapter 5 . Optical Systems M ake use of Mirrors and Lenses!. 5.1 The Ray Model of Light. 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.

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Chapter 5

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Chapter 5

Optical Systems

Make use of Mirrors and Lenses!

5.1 The Ray Model of Light

  • 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

Light and Matter

  • 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)

Diagrams of How Light is Reflected and Refracted


  • You can predict shadows using the ray model of light

  • Size of shadows are related to distance from the light source

Light can be Reflected

  • •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

The Law of Reflection

•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

Light Can Be Refracted

  • •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

Refraction of Light in Air

  • Can occur when light passes through air of different temperatures

  • Warm air is less dense than cold air

  • Results in a mirage

Homework Time

Textbook questions

Page 181

Questions # 1-7, 9

There will be a homework check! 

5.2Using Mirrors to Form Images

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

How Do Reflected Rays Form an Image That We See in a 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

Image Size, Distance and Orientation

  • 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

Concave Mirrors

  • •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

Concave Mirrors

  • •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

Convex Mirrors

  • •Curves outward, opposite to concave, diverging rays are given off

  • •Image is always upright and smaller then the actual image

Convex Mirrors

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

Homework Time!

  • Textbook questions

  • Page 189

  • Questions #1-5

5.3Using Lenses to Form Images

  • •Lens = a curved piece of transparent material that refracts light rays to either diverge or converge

  • •Can be either convex or concave

Concave Lenses

  • •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

Convex Lenses

  • 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 in Convex Lenses

  • •Focal length = distance between the lens/mirror and the focal point

  • •This has been mathematically determined for distance of object

Focal Length and Image Formed

Work Time !

Textbook Questions

Page 197

Questions # 2-7, 11

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