light is energy the term “light” can describe many different forms of electromagnetic energy

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!