Light and OpticsWhat is light?

It's a kind of energy called "electromagnetic (EM) radiation" (but this kind of radiation is

not harmful, except for an occasional sunburn).

There are other kinds of EM radiation too (radio waves, microwaves, x-rays, etc.), but

light is the part WE can see, the part that makes the rainbow.

How does light travel?FAST and STRAIGHT.

• How FAST?About 186,000 miles per second [300,000 kilometers per second], so light from the sun takes about 8 minutes to go 93 million miles [149 million kilometers] to earth. Does this seem SLOW? Well, if you could DRIVE to the sun at 60 mph [100 kph], it would take you 177 years to get there! In one second, light can go around the earth 7 times!

• Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 7 times in one

second.

How STRAIGHT?Perfectly straight, until something bends it. The

straight paths of light are called LIGHT RAYS.

Properties of Light• Light travels in straight lines:

Laser

• Light travels much faster than sound. For example:

1) Thunder and lightning start at the same time, but we will see the lightning first.

2) When a starting pistol is fired we see the smoke first and then hear the bang.

There are three ways to control light.

Block itwith something opaque that creates a shadow

Reflect itby changing its path with a mirror

Bend itChange its direction by making it pass into another transparent material of

different density, like glass or water. This is called REFRACTION, and it's how lenses work.

• Shadows

Shadows are places where light is “blocked”:

Rays of light

Law of Reflection

The angle of incidence equals the angle of reflection.

The incident ray strikes the mirror.

The reflected ray bounces off.

• The Law of Reflection

Angle of incidence = Angle of reflection

In other words, light gets reflected from a surface at the same angle it hits it.

Reflection

• In specular reflection each incident ray bounces off in a single direction.

• A surface that is not shiny creates diffuse reflection. • In diffuse reflection, a single ray of light scatters into many

directions.

• We see things because they reflect light into our eyes:

Homework

Reflection

• Images appear in mirrors because of how light is reflected by mirrors.

• The incident ray follows the light falling onto the mirror.

• The reflected ray follows the light bouncing off the mirror.

Refraction

• Light rays may bend as they cross a boundary from one material to another, like from air to water.

• This bending of light rays is known as refraction.

• The light rays from the straw are refracted (or bent) when they cross from water back into air before reaching your eyes.

Refraction

Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this:

In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______.

Words – speed up, water, air, bent

Reflection and Refraction

• A lens is an optical device that is used to bend light in a specific way.

• A converging lens bends light so that the light rays come together to a point.

• A diverging lens bends light so it spreads light apart instead of coming together.

Reflection and Refraction

• Mirrors reflect light and allow us to see ourselves.• A prism is another optical device that can cause light to change

directions. • A prism is a solid piece of glass with flat polished surfaces.

The fine print:

There are actually other ways to bend or deflect light, including diffraction gratings

and holographic lenses. These depend on the wave nature of light, and are a little more difficult to explain. Scientists have also

found that gravity can bend light, but it takes a very large object with strong gravity such as a star to bend light very much, so it's not an

effect you see every day!

Visible light waves are the only electromagnetic waves we can see. We see these waves as the

colors of the rainbow. Each color has a different wavelength. Red has the longest

wavelength and violet has the shortest wavelength. When all the waves are seen

together, they make white light.

Spectrum Wavelengths

When white light shines through a prism, the white light is broken apart into the colors of the visible light spectrum. Water vapor in the atmosphere can

also break apart wavelengths creating a rainbow.

Dispersion and prisms

• The variation in refractive index with color is called dispersion.

• A rainbow is an example of dispersion in nature.

• Tiny rain droplets act as prisms separating the colors in the white light rays from the sun.

Mirrors, Lenses, and ImagesWe see a world of images created on the retina of the

eye by the lens in the front of the eye.

Mirrors, Lenses, and Images• Objects are real physical things that give off or reflect light rays. • Images are “pictures” of objects that are formed in space where light rays meet.

Mirrors, Lenses, and Images

• The most common image we see every day is our own reflection in a mirror.

• The image in a mirror is called a virtual image because the light rays do not actually come together.

The virtual image in a flat mirror is created by the eye and brain.

Mirrors, Lenses, and Images

• Light rays that enter a converging lens parallel to its axis bend to meet at a point called the focal point.

• The distance from the center of the lens to the focal point is called the focal length.

• The optical axis usually goes through the center of the lens.

The image formed by a lens

• A lens can form a virtual image just as a mirror does.• Rays from the same point on an object are bent by the lens so

that they appear to come from a much larger object.

The image formed by a lens

• A converging lens can also form a real image. • In a real image, light rays from the object actually come back

together.

METRO WAN

METRO WAN

TRANS-OCEANIC

V

Technological Revolution in Optics

Communication by photons

Massive optical data storage

Precision laser machining

Medical laser therapy & optical imaging

Blu-ray disc (25GB)CD/DVD

Telephony/data/internet

Laser cutting

Laser writing on human hair Photolithography for manufacture

of computer chips

Corrective laser eye surgery 3-D laser imaging of cell

Optics has an important place in history

Telescope observations forged our understanding of the Universe

Microscopes revealed a micro-universe

Optics, light & vision has been vital for human survival

Today, Optics remains a key scientific diagnostic technique (e.g. imaging).

A new revolution in Optics has emerged with the birth of the laser, fibre optics, integration of optics and electronics, etc..

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Snell’s Law

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REFLECTION REFRACTION

DIFFRACTION INTERFERENCE

Fundamentals of Optics

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POLARISATION

EM-theory

© 2003 Mike Maloney 35

Our Eyes

Vision Correction with Lenses

c. Hyperopia (farsightedness)

a. Normal eye

b. Myopia (nearsightedness) Corrected with concave lens

Corrected with convex lens

No correction needed

A light review:• Our primary source of light is the sun.• Light travels in straight lines at a speed of

186,000miles per second.• Light waves travel faster than sound waves.• Light energy from the sun travels through space ,

reaches earth, and some of it turns to heat energy and warms the earth’s air.

• Light from the sun also travels to the cells of green plants (producers) and is stored as energy.

• When light reaches an object, it is absorbed, reflected, or passes through it.

*Electromagnetic Radiation• Electromagnetic radiation can be described in terms of

a stream of photons. Each photon is traveling in a wave-like pattern, moving at the speed of light and carrying some amount of energy.

• The only difference amongst radio waves, visible light, and gamma-rays is the amount of energy of the photons. Radio waves have photons with low energies. Microwaves have a little more energy than radio waves. Infrared has still more energy.

• As we move down the chart we see visible, ultraviolet, X-rays, and gamma-rays whose photon energies gradually increase.

• Gamma and Cosmic rays have the highest energy waves.

*Slide info from NSTA 2004 conference

Remember radio waves are long…and gamma rays are small

Radio-TV -Microwave- Infrared - VISIBLE -Ultraviolet -X-rays - Gamma- Cosmic

Essential KnowledgeProperties of a wavelength

Vocabulary• Waves: a disturbance which carries energy and that travels away from the starting point.• Wavelength: the distance between one crest of a wave and the next crest (distance between compressions); red is longest and violet is shortest• Peak: the highest point of a light wave• Trough: the lowest point of a light wave• Frequency: the number of waves (light or sound) produced in a given unit of time, such as a second

Vocabulary• Reflection: the bouncing of light from a surface• Refraction: the bending of light as it passes through one material to another

Vocabulary• Transparent: materials that allow all light to pass through• Translucent: letting light through but scattering it• Opaque: materials that do not let light through• Transmit: to send (as in sound or light). It also means light passing through an object.

Galileo Galilei• Italian• Lived from 1564-1642• Developed the refracting telescope• Developed the first known example of the microscope

Robert Hooke• English• Lived from 1635-1703• Devised the compound microscope and illumination system• Discovered plant cells• Examined fossils with a microscope

Isaac Newton• English• Lived from 1643-1727• Discovered that white light was not a simple entity, but splits into a range of colors• When he passed white light through a glass prism, he noted that a spectrum of light was formed; particle theory of light• Reflecting telescope