# Light is Energy The term “Light” can describe many different forms of electromagnetic energy.

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Light is Energy The term “Light” can describe many different forms of electromagnetic energy.

Electromagnetic Spectrum

Long wavelength --> small frequency Short wavelength --> high frequency increasing frequency increasing wavelength

Spectrum of White (Visible) Light

The Visible Spectrum COLOR FREQUENCY (Hz)WAVELENGTH (nm) Red 4.0  4.8 x 10 14 700-630 Orange 4.8  5.1 x 10 14 630-590 Yellow5.1-5.4 x 10 14 590-560 Green5.4-6.1 x 10 14 560-490 Blue6.1-6.7 x 10 14 490-450 Violet6.7-7.5 x 10 14 450-400

Electromagnetic Spectrum In increasing energy, ROY G BIV

Light is an electromagnetic wave Or is it a Particle acting like a wave?

Nature of Light Like sound waves, light exhibits properties of waves. These are diffraction, reflection, refraction and interference. In addition, light waves also exhibit dispersion and polarization. Unfortunately, Light cannot be completely described by the Wave theory.

Nature of Light Light has particle-like properties as shown by Einstein's Photo-electric effect. Light is said to travel in photons or small packets of NRG. The Explanation  Dual-nature of light

Diffraction of Light Particle Wave

The Principle of Reflection The Angle of Incidence = The Angle of Reflection

Mirror Image Image formation from a plane mirror Image appears at a distance equal to the object distance. Image is the same size as the object.

Refraction The bending of light upon entering a medium with with a different density. A light wave will speed up or slow down in response to a changing medium.

Beach Party Imagine lines of people rushing from the parking lot to the sandy beach. People can run faster on pavement than in the sand. Pavement Sand

Beach Party Pavement Sand

Beach Party Pavement Sand

Beach Party Pavement Sand

Beach Party As people enter the sand, they slow down. Pavement Sand

Beach Party Pavement Sand

Beach Party Pavement Sand

Refraction Light waves, like people waves, will slow down and bend or refract.

Refraction As a wave enters a piece of glass its velocity slows down and the wave is bent towards the normal line. As it exits it will speed up and is bent away from the normal line. Air Glass medium Surface Normal Incident Angle

Dispersion Light of different frequencies is refracted by different amounts Red Light (lower frequency, longer wavelengths) is bent the least. Blue Light (higher frequency, shorter wavelengths) is bent the most. Refraction is Dispersive

The Beauty of Dispersion and Refraction

Rainbows

Wave Speed v =  Sound (in air) ~ 344 m/s Light (in vacuum) ~ 3x10 8 m/s What is the wavelength of a sound wave which has a frequency of = 1000 Hz? 344 m/s = 1000 Hz = 344m/s/1000/s (Seconds cancel) = 0.34 meters 1/3 of a meter in size, 1000 of them each second!

Wave Speed c =  Sound (in air) ~ 344 m/s Light (in vacuum) ~ 3x10 8 m/s What is the wavelength of a radio wave with  = 94.1 FM? AM kHZ = 10 3 Hz FM MHz = 10 6 Hz 3x10 8 m/s = (94.1 x 10 6 Hz) = 3x10 8 m/s / 94.1 x 10 6 /s = 3.2 meters 3 meters in size, 94,100,000 of them each second!

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