
Unit C: Lights & Optics

Our knowledge about light and vision comes from explanations, inventions, and
investigations.

1.1: The Challenge of Light

Although for centuries we know how to use light to satisfy our needs, we couldn’t explain
how light works. Here are some ideas about light:

Early Light Ideas

1st idea – _____________ (Greek) [6th BC]


Human produced straight beams of light from our _____________, when they hit
an object they could see it.

Problem – We cannot see in the dark.
2nd idea – _____________ (Greek)

Discovered that light travels in _____________lines

Discovered the Law of _____________



Angle between Incident ray & Normal = Angle of Reflected ray &
Normal

_____________Ray- a ray approaching a surface

_____________Ray- a ray that leaves or reflects a surface at the
point of incidence

Point of _____________- where an incident ray strikes the surface

_____________- an imaginary line drawn perpendicular to the
surface at the point of incidence
3rd idea – _____________ (Greek) [1st AD]

Discovered that light _____________as it passes from air to glass.

Light travels _____________through air than in fluids
4th idea – al-Haytham (Arab) [1000 AD]


First to accurately describe how _____________worked.

Light bounces off objects and then travels to the eyes, not what Pythagoras
thought!
5th idea – _____________ (English)


By shining a light through a prism he demonstrated that white light is actually a
mixture of different _____________of light.
6th idea – Ole Romer (U.S.A.) [1676]

First reasonably accurate measurement of the _____________of light.

Albert A. Michelson (USA) [1920] Refined Romer’s experiment by
using the tops of two mountains. 299 798 km/s p.181 for picture
4 Basic Properties of Light

Due to these, and other people, we can conclude 4 principles of light:
1) Light travels in _____________lines.
2) Light can be _____________.
3) Light can bend by travelling in different _____________
4) Light is a form of _____________.
1.2 Optical Devices

Optical Device: any device that uses _____________



Ex) mirrors, lenses, microscopes, and telescopes
_____________: optical devices used for viewing very small objects; has at least two
lenses: the objective lens and the eyepiece lens.

Different kinds: compound (including dissecting & electron)

First invented by Hans and Zacharias Jansen in Netherlands (1595)

Antonie van Leeuwenhoek: created a more powerful and useful design. First one
to identify micro-organisms.
_____________: optical device for viewing distant objects; there are two types: reflecting
and refracting telescopes.

Galileo did not invent the first one but created many stronger telescopes and
made many important astronomical discoveries.

Telescopes use mirrors and lenses (or both) to do two things:

1)
_____________ (ex. to see a planet!)
2)
Collect _____________ (see faint objects of a planet)
Types of Telescopes
(i) _____________Telescope – telescope that uses two lenses, each at the
end of a long tube to from an enlarged image.
(ii) _____________Telescope – telescope that uses a curved mirror and a
lens to form an enlarged image.

_____________: device for viewing distant objects made up of two short refracting
telescopes fitted together.
2.1 Light Behaves in Predictable Ways

_____________Diagrams – diagram used to represent how light travels; each ray has a
straight _____________to show the direction of travel.

_____________– brightness of light; amount of light arriving per unit area at a place.

A light meter measures the intensity of light

Further the light source the lower the intensity = fewer rays reach your
eyes.

Explains how shadows are places where light rays are blocked.

If light hits an object, it can’t go any father
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P. 190
Light Interacts with Materials

_____________– describes materials that allow light to pass through with little or no
reflection; Ex) glass.

_____________– describes materials that allow some light to pass through;
Ex) frosted window.
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_____________– describes materials that do not allow light to pass through; Ex) wood,
books

Non-_____________– describes objects that do not produce light but may reflect it; most
objects on earth are non-luminous Ex) wood.

_____________– describes objects that produce light; Ex) sun & fire
Types of Reflection

_____________Reflection – reflection that happens when parallel rays hit a smooth
surface; all rays reflect at the same angle.


Your eyes must be in line with the reflected rays to get a clear image.
_____________Reflection – reflection that happens when parallel rays hit a rough
surface; all rays reflect at different angles.

Object can be seen from any position.
2.2 The Law of Reflection

_____________ (incoming) Rays – ray of light that arrives at a mirror or other
substance.


The shinier and smoother the surface the better the reflection.
_____________Mirrors – flat mirror; reflecting surface that has no curvature.
The Law of Reflection

When a ray of light hits a plane mirror at an angle it bounces off the mirror surface at
exactly the same angle.
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_____________– line perpendicular to a surface (90º angle to the surface)

This is an _____________line coming out from the point of incidence

Angle of _____________– angle between the incident ray and the normal.

Angle of _____________– angle between the reflected ray and the normal.

Law of Reflection – angle of incidence of a wave hitting a surface equals the angle of
reflection. All _____________obeys this law.
Angle of
Incidence
=
Angle of
Reflection
2.3 Reflecting Light with Curved Mirrors

_____________Mirror – reflecting surface that is curved inward like the inside of a
bowl or a spoon; light rays reflected from it converge (come together).

Useful to collect light and direct it to a single point.

Ex) reflecting telescope or car headlights

_____________Point – point at which light rays meet, or appear to meet, after being
reflected by a mirror, or refracted by a lens.
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Concave Mirror Images

Image from a concave mirror depends on the object’s distance from the focal
point.
Position of Object
(I) Object far from the focal point
Image
Upside-down image
Smaller Size
(II) Object closer to the focal point
Upside-down image
Larger Size
(III) Object on the focal point
No Image
(IV) Object between the focal point & mirror

Upright image
Enlarged
Drawing Rays 4 Steps: There is a trick to this!

You need to understand that light travels in straight lines

You need to know that one light ray (incident and reflected) must always travel
through the focal point!
1. Take the top of the object & draw an incident ray going parallel and one going through
the focal point
2. Once the rays hit the mirror, the opposite is true; the incident rays turn into reflected
rays. The incident ray that was parallel must now go through the focal point, and the
incident ray that went through the focal point must go parallel.
3. Mark the spot the reflected rays intercept
4 .This point of interception is always the top of the object.
Convex Mirrors

_____________Mirrors – reflecting surface that bulges out like the back of a spoon;
light rays reflected from it diverge (spread out).

The image appears like it is originating from a smaller point behind the mirror;
useful for side mirrors.
2.4 Transparent Substances Refract Light

When a light ray strikes a boundary where two different substances meet (interface) at an
angle, it will change direction.

Human eyes assume the light rays move through the interface in a straight line so we
incorrectly identify where an object is in the other substance.
How Light Refracts

_____________– bending of light as it ravels from one material to another material.


Refraction occurs because the speed of light changes in different substances.
In space (vacuum) = Light travels at 300 000 km/s

There are no particles in space, what happens when light strikes particles? It
slows down : Bends towards the normal.

As a result… The _____________the new medium = the more the light
_____________down and refracts.

may occur due to the number of _____________in the material

Light goes from air to water (or glass) bends _____________normal

Light goes from water (or glass) to air  bends _____________from normal
2.5 Lenses Refract and Focus Light

_____________– curved piece of glass or other transparent material that refracts light in
a predictable way, useful because the light rays that refract can form images.

Lens ability depends on:
1)
_____________of lens
_____________of the lens
2)
Types of Lenses

_____________Lens – piece of transparent material that is thinner in the middle than at
the edges; light rays passing through it diverge or spread out.

_____________Lens – piece of transparent material that is thicker in the middle than at
the edges; light rays passing through it converge or come together.


Technical name for a lens that curves out on both side = double convex lens.
Recall: Light rays refracted through a lens meets at the focal point.
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Useful for two reasons:

1) Good _____________collector Ex) refracting telescope
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2) Forms a _____________Image
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Real Image is an image that looks like a real object.
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Size of an image depends on the distance of the object from the
lens.

Main Drawback is that the image produced is _____________.
Image Formation with a Convex lens
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Much like a concave mirror had 4 possibilities, so does a convex lens

Image formed depends on how far the object is from the lens
Position of Object
Image
(I) Object far from the focal point
Upside-down image
Smaller Size
Real Image
(II) Object closer to the focal point
Upside-down image
Larger Size
Real Image
(III) Object on the focal point
No Image
(IV) Object between the focal point & lens
Upright image
Enlarged
Same side as object
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Nearsightedness- can see near but not far because focal point is in front of retina

Farsightedness – can see far but not near because focal point is behind retina
3.1 The Wave Model of Light
Properties of Waves

_____________: the height of the wave, measured in meters.
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_____________: the distance between adjacent crests
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_____________: the time it takes for one complete wave to pass a given point
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_____________: the number of complete waves that pass a point in one second
Light Waves

White light is refracted and splits into the colors of the rainbow

Produces __________________________spectrum

Colors of visible light: Each color of light is refracted at a different angle

White light being refracted produces the colors of visible light
Wave Model of Light

Model used to explain the characteristics and behavior of light energy

Light is an energy in the form of waves

Different colors of light have different wavelengths

Waves with shorter wavelengths have higher energy than those with longer wavelengths
3.2 The Electromagnetic Spectrum

Whole world of energy that we cannot see

Wavelengths that make up visible light are a small part of _____________radiation

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All forms of radiant energy
Human eyes can only see a very small portion of this spectrum (the visible light
component)
Application of electromagnetic radiation

Although we can’t see, these waves behave just like visible light (reflected, absorbed,
transmitted)

Radio Waves
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Radio, MRIs
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Microwaves
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Microwaves,
RADAR
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UV light (vit D
synthesis)
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Ultraviolet rays
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Gamma Rays
3.3 Producing Visible Light

2 types of light:


_____________light sources
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Bioluminescence (photophore)
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Sunlight
_____________light sources
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Incandescent light
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Phosphorescent light

Fluorescent light

Energy efficient light
bulbs
Artificial Light Sources

Incandescent Light : Filament, where electrical energy flows through and heating it to
extremely high temperatures

Fluorescent light: Glass tube filled with mercury vapour gas and coated with a white
powder (phosphor)

Electricity passes many times/ sec emitting UV.



When the UV hits the phosphor produces the light
Phosphorescent light
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Slightly different from fluorescence

UV light hits phospor and stores up energy

Emits light after uv light has stopped and glows in dark
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Usually in novelty items
Which is the best?

Many factors come into play:

Cost

Appearance
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Convenience

Durability
Natural Light Sources

Bioluminescence is the production and emission of light by a living organism as the
result of a chemical reaction during which chemical energy is converted to light energy.

Chemical reaction produced by photophores
3.4 The Colours of Light : Adding Colours Together

Visible light has a spectrum of colours, each having a slight different _____________


Each color refracts by a slightly different amount
All combined together form white light
Primary Colours

All you really need to produce white light are three colours:
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Red, green, blue

By mixing the right intensities of each color you get white light
Secondary Colours
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Colours made by combining any two of the primary colours of light
4.1 Image Formation in Eyes and Cameras
How Light Gets In

Both eyes (natural) and cameras (artificial) are image producing technologies.

A camera is very similar to how an eye works:
Similarities
Eye
Camera
How does light enter?
Pupil
Aperture
What controls the amount of light?
Iris
Diaphragm
What interprets the image?
Retina
Film
How is the light focused?
Lens
Lens

Shutter - is like a set of doors that opens when you take a picture, the longer it is open the more
light that strikes the film in a camera
Eye Anatomy

-The _____________is the opening; the amount of light that enters is controlled by the
iris.

The _____________is made up of a circular band of muscles.
Iris Controlling the Light

In bright light the iris constricts, becoming _____________, and reduces the light.

In dim light the iris dilates, becoming _____________, and increases the light.
When Light Gets Inside…

To see, the light must hit the sensitive retina at the back of the eye, which has 2 types of
light sensitive photoreceptors.
1)
2)
_____________- highly sensitive to small amounts of light (dim light).

allows for seeing in the dark (when there is enough light reflected!!)

more rods on the outside of the retina
_____________- sensitive to bright lights, and they detect colour.

almost exclusive in the retina

Cones can’t function in low light, so we only see shades of gray in low
light because only rods are stimulated
Focusing the Light
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In order to form a clear & sharp image the focal point must land on the retina.

In the eye there are muscles that control the shape of the lens.

In a camera the lens is moved forward and backward.

The upside-down image produced by the lens is not a problem because the brain
interprets the world right side up, and film can be developed either way.
Correcting Vision Problems with Lenses

Nearsightedness –can see near, but cannot see far.


the eye cannot make the lens thin enough to focus the light on the retina, so a
concave lens is used to converge the light onto the retina.
Farsightedness - can see far, but cannot see near.

the eye cannot make the lens fat enough to focus light on the retina, so a convex
lens is used to diverge the light onto the lens.
Laser Eye Surgery

the lens is reshaped by a laser (helps focus light).
Night Vision Goggles

- the low light is intensified by phosphor-coated screen (looks green).
4.2 Other Eyes in the Animal Kingdom
Similarities between human and animal eyes

Humans, like most vertebrates have a rounded cornea, lens, and retina, which are referred
to as _____________eyes.
How do eyes function for different animals?

Fish - have a perfectly round _____________sticking out of the pupil, which allows them
to detect danger from all directions since they do not have necks.

Birds - have _____________, instead of, 3 cone receptors (RGB) which helps because
they must see from further distances because they fly.

Nocturnal animals - are usually awake at night, they have many more _____________to
capture more dim light, and they have very large pupils, to capture more light. They also
have a layer called the tapetum lucidum, which reflects the low light to the retina.

Octopus - an invertebrate with camera eyes, but lens is _____________instead of shaped.
Compound Eyes

Insects and Crustaceans have compound eyes, which are make up of many individual
units called _____________

these eyes are great for detecting movement, but not for creating a single coherent
image.

Do not see color

Do not see 1 image, but many small images put together
4.3 Image Storage and Transmission Font

The brain sends and receives signals as electrical impulses traveling across neurons, but
scientists still don’t understand how the images are stored.

If you take any form of information and convert it into numbers, that’s digital.
Stadium Images

The process of creating a big picture out of _____________pieces. P.240 figure 4.19

Like ones created in a stadium is similar to the process of digital imaging.
Digital Images

Therefore, stadium images are analogous to _____________images

When a computer receives an image, it divides the picture up into small elements called
pixels (picture elements), like the individual seats in a stadium.
Coloring Digital Images

To color a digital image, the computer assigns a value to each _____________which
corresponds to a certain color. p. 241 Fig 4.21
Digital Image Quality

The quality of a digital image depends on the _____________.

A picture with lots of small pixels has a better resolution than a picture with a smaller
number of large pixels.
Capturing Digital Images

In a digital camera, the light falls onto a charge-coupled device (CCD), which is a grid
similar to a piece of _____________paper.
Transmitting Digital Images

The first major advantage of digital imaging is that it can easily be sent great
_____________, the second is that it can collect others parts of the
_____________spectrum (such as infrared).