NATURE OF LIGHT

• It is an electromagnetic wave, a form of energy that can travel freely across space.• The energy light is also called

radiant energy.

What is Light?

Kinds of Radiant EnergyInfrared Rays Radio Waves

Ultraviolet rays X-rays

SOURCES OF LIGHT

Light sources can be classified in to two types:• Natural Light• Artificial Light

How Light Is Produced• All light come from atoms• It is produced by atoms that have

gained energy either by absorbing light from another source or being struck by other particles.• An atom with such extra energy is

said to be excited

• Light is usually described as a wave, shaped much like a water wave that moves across a lake.• Light can also be described as a

small particle, called photon• One way to excite atoms so that

they emit light is by heating them.

OTHER SOURCES of LIGHT• Emission of light by a substance not

resulting from heat is called luminescence• Some luminiscent materials glow in the

dark long after they have received extra energy. They are said to be phosphorescent

• Fluorescence is the emission of light by a substance that has absorbed light

• Bioluminescence is the production and emission of light by a living organism.

• Aurora is an emmision of light by molecules of air

• Laser is a device that produces a powerful, narrow beam of light in which all the photons have the same energy and travel in the same directions.

• During most of the 1800’s, scientists thought of light as a wave that travels much like a water wave. This idea of light as a wave was popular because it explained experiments in which light created a series of bright and dark lines called inference pattern.

• Water waves-travel across the surface of

the water while the water itself only moves up and down.

By the late 1800’s, scientists had concluded that l ight waves consist of region of force known as electric fields and magnetic fields .

• A simple model of a light wave begins with a ray (a straight line) that shows the direction of the light’s travel.

• Perpendicular (at right angles), short arrows represent the electric field.

• Light waves resemble other types of waves in some features, including wavelength, frequency , and amplitude.

• Wavelength- is the distance along a straight l ine from one crest (peak) of the wave to the next.

• Frequency - is the number of times each second that crests pass a stationary checkpoint.

• Amplitude - is the greatest distance of a crest or tough ( low point) from the ray.

A simple relation exists between a wave’s frequency and wavelength: • The higher the frequency, the shorter the

wavelength.

Light is a transverse wave, meaning that the vibrations are perpendicular to the

motion and speed of the wave.

Electromagnetic Waves

• Because light consists of electric and magnetic fields, it is called an electromagnetic wave.

• The term light commonly refers to just those electromagnetic waves that we can see. For light to be visible, it must have a wavelength within a certain narrow range of values called the visible spectrum.

Violet Light- has the shortest wavelength that is visible.Red Light- has the longest wavelength that is visible.