The Ray Model of Light study guide meaning and definition

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The Ray Model of Light study guide meaning and definition

Chapter 5 Notes

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)

Shadows

You can predict shadows using the ray model
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

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 reflected rays form an image that we see in a mirror?

The reflected light that bounces of 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 and Distance

Both will be the same when using a plane mirror

Image Orientation

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
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
Main characteristics: 1. Objects appear to be smaller than they are
More objects can be seen than in a plane

mirror of the same size

Used for security mirrors, on cars

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

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 than the edge
Light rays converge meeting at a focal point
Image depends on the placement of the lens and the object

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

Distance of Object from Lens	Type of Image Formed
More than 2 focal lengths	Smaller, inverted
Between 1 and 2 focal lengths	Larger, inverted
Object at focal length	No image
Less than 1 focal length	Larger, upright

Source : http://fc2.sd23.bc.ca/~jreed/FOV1-00087E5F/FOV1-00087E9C/FOV1-0008800B/Chapter%205%20Notes.doc

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