# Chapter 5 - PowerPoint PPT Presentation

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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

### Transparent

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

• of light is absorbed and reflected

• (Example: air, water, and glass)

### Translucent

•Most light rays get through but they are scattered

in all directions (Example: frosted glass)

### Opaque

• •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

### Work Time !

Textbook Questions

Page 197

Questions # 2-7, 11