light is energy the term “light” can describe many different forms of electromagnetic energy
TRANSCRIPT
Light is Energy
The term “Light” can describe many different forms of electromagnetic energy.
Electromagnetic Spectrum
Electromagnetic SpectrumElectromagnetic SpectrumElectromagnetic SpectrumElectromagnetic Spectrum
Long wavelength --> small frequencyLong wavelength --> small frequency
Short wavelength --> high frequencyShort wavelength --> high frequency
increasing increasing frequencyfrequency
increasing increasing wavelengthwavelength
Spectrum of White Spectrum of White (Visible) Light(Visible) Light
The Visible Spectrum
COLOR FREQUENCY (Hz) WAVELENGTH (nm)
• Red 4.04.8 x 1014 700-630 • Orange 4.85.1 x 1014 630-590• Yellow 5.1-5.4 x 1014 590-560• Green 5.4-6.1 x 1014 560-490• Blue 6.1-6.7 x 1014 490-450• Violet 6.7-7.5 x 1014 450-400
ElectroElectromagneticmagnetic SpectrumSpectrum
ElectroElectromagneticmagnetic SpectrumSpectrum
In increasing energy, RIn increasing energy, ROOYY GG BBIIVV
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 withwith 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
IncidentAngle
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) ~ 3x108 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) ~ 3x108 m/s
What is the wavelength of a radio wave with = 94.1 FM?
AM kHZ = 103 Hz
FM MHz = 106 Hz
3x108 m/s = (94.1 x 106 Hz)
= 3x108 m/s / 94.1 x 106 /s
= 3.2 meters
3 meters in size, 94,100,000 of them each second!