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

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


Transparent

Transparent

  • •Light can pass through freely, only a small amount

  • of light is absorbed and reflected

  • (Example: air, water, and glass)


Translucent

Translucent

•Most light rays get through but they are scattered

in all directions (Example: frosted glass)


Opaque

Opaque

  • •Prevents light from passing through

    (Example: cardboard)


Diagrams of how light is reflected and refracted

Diagrams of How Light is Reflected and Refracted


Shadows

Shadows

  • 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

5.2Using 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 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

5.3Using 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

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


Focal length and image f ormed

Focal Length and Image Formed


Work time

Work Time !

Textbook Questions

Page 197

Questions # 2-7, 11


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