The Nature of Light

The Dual Nature of

Light

The Electro Magnetic Spectrum

Opaque, Transparent

and Translucent

Different Sources of

Light

The Dual Nature of Light

Light as a wave

Light as a

particle

The WAVE Theory of Light The theory that lights is transmitted via

wave form was proposed by Christian

Huygens in 1679. According to the

theory:•light corpuscles have mass and travel at extremely

high speeds in straight lines

•rectilinear propagation - blocked by large objects

(well-defined shadows)

•obey the law of reflection when bounced off a surface

•speed up when they enter denser media

•paths in denser media "bend towards the normal"

•prism dispersion - contradicted corpuscular theory

The Particle Theory of Light•wavelet envelop model (each point on a wavefront

acts as a source for the next wavefront)

•plane waves generate plane waves, circular waves

generate circular waves

•light was composed of longitudinal waves like sound

•obey the law of reflection when bounced off a surface

•waves slowed down when they entered a denser

medium causing their paths to "bend towards the

normal"

•light SHOULD produce interference patterns and

diffraction patterns

The theory that light is transmitted via corpuscar form was supported and advocated by Sir Isaac Newton. According to his theory:

The Electromagnetic Spectrum

The electromagnetic spectrum is the range of all

possible frequencies of electromagnetic radiation.

Electromagnetic waves are formed when an electric field

couples with a magnetic field.  It is a continuum of all

electromagnetic waves arranged according to frequency,

wavelength and energy.

frequency, wavelength and energy

• Wavelength is inversely proportional to the wave frequency

• Photon energy is directly proportional to the wave frequency

λ = E / f

Electromagnetic Spectrum:Radio Waves

Microwaves

Infrared Radiation

Visible Light

(Light)

Ultraviolet Light X-rays

Gamma Rays

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Radio waves Microwaves

•Have the longest wavelengths but least energetic

•Utilized by antennas

•They are used for transmission of data, via modulation.

•Television, mobile phones, wireless networking, and amateur radio all use radio waves.

•Very easily absorbed by water

•Cause water and fat molecules to vibrate, which makes the substances hot.

•Good for transmitting information because microwave energy can penetrate haze, light rain and snow, clouds, and smoke.

•Mobile phones, fixed traffic speed cameras, and radar, which is used by aircraft, ships and weather forcasters, all use microwaves.

Infrared Radiation

Visible light waves are the only

electromagnetic waves we can

see. We see these waves as the

colors of the rainbow. 

Light

•Can be detected by special infra-red film.

•Primary source of infrared radiation is heat or thermal radiation

•Our skin emits infrared light, which is why we can be seen in the dark by someone using night vision goggles.

•Ex. remote control

UV rays X-rays•Main natural source is the sun and other stars

•Can break chemical bonds, making molecules unusually reactive

•Often harmful to plants and animals, including humans

•Used to kill microbes, getting a sun tan, detecting forged bank notes

•Also called as Roentgen rays in honor of their discoverer

•Given off by stars and are strongly emitted by some types of nebulae.

•Have so much energy and such a short wavelength that they can go right through you

• Used by doctors to see inside people

Gamma Rays

•Shortest-wavelength, Highest energy

•Most dangerous and most penetrating of all electromagnetic radiation, and are quite difficult to stop

•Result of violent cosmic events such as supernovas, other nuclear explosions, and radioactive decay

•Used to kill cancer cells ("Radiotherapy")

Light Sources

Light is a form of energy.  To create light, another form of energy must be supplied.  There are two common

ways for this to occur, incandescence and luminescence.

"Black body radiation"

It is the emission of light from a hot body as a result of its temperature.

Involves the vibration of entire atoms

Sunlight, regular light bulbs (not florescent) and fires are all incandescent sources of light.

"Cold light"

It is the emission of light by a substance not resulting from heat. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal.

Involves only the vibration of electrons

Ex. computer monitors, televisions, and florescent lights, fireflies

Incandescence

Luminescence

Luminous and Illuminated

BodiesThe objects that we see can be placed into one of two

categories: luminous objects and illuminated objects. Luminous

objects are objects that generate their own light. Illuminated

objects are objects that are capable of reflecting light to our

eyes.

A luminous body, such as the sun, another star,

or a light bulb, is thus distinguished from an

illuminated body, such as the moon and most of

the other objects one sees. Luminous objects

give off light whereas illuminated objects

relfect light. Examples of luminous bodies are

the sun, stars, fireflies, lighted candle, light

bulbs..Illuminated bodies not only reflect

light but sometimes also transmit

it, such as the opaque,

transparent and translucent

materials. An example of an

illuminated body is the moon.

Opaque, Translucent or Transparent?

Water

Plastic Bags

Wind

Wood

Tissue Paper

Books

c

Glass

Translucent Objects•These kinds of objects scatter or disperse light when light falls on them.

•They are said to transmit light in the absence of details

•You can only see a blur image when you peek through these

•Frosted glass and waxed paper are examples of translucent objects.

Transparent Objects•They are those that allow

light to pass through readily.

•These kind of objects have

absolute clarity.

•You can see right through

them.

•The water, air and glass are

all transparent objects.

Opaque Objects

•These objects do not allow light to pass

through.

•They absorb some of the light that is cast on

them.

•Wood, paper and many more are examples of

such objects.