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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

Chapter 5

Optical Systems

Make use of Mirrors and Lenses!

5 1 the ray model of light
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
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)


  • 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
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
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
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
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
Homework Time

Textbook questions

Page 181

Questions # 1-7, 9

There will be a homework check! 

5 2 using mirrors to form images
5.2 Using 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 r eflected r ays f orm an image t hat w e s ee in a 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
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
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 mirrors1
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
Convex Mirrors

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

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

Convex mirrors1
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 time1
Homework Time!

  • Textbook questions

  • Page 189

  • Questions #1-5

5 3 using lenses to form images
5.3 Using 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
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
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 in Convex Lenses

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

  • • This has been mathematically determined for distance of object

Work time
Work Time !

Textbook Questions

Page 197

Questions # 2-7, 11