Galileo Galilei (1564 – 1642)

SUNSPOTS

“Revealing great, unusual and remarkable spectacles, opening these to the consideration of every man, and especially of philosophers and astronomers….”

What is Light?What is Light?

Properties of WavesProperties of Waves

All electromagnetic waves travel at the same speedThe speed of light: 300,000,000 m/s

trough

crest

Wavelength

(length/cycle)

Wavelength (): the length of one complete cycle

trough

crest

Properties of WavesProperties of Waves

All electromagnetic waves travel at the same speedThe speed of light: 300,000,000 m/s

Wavelength

(length/cycle)

Amplitude: 1/2 height between trough and crest

Amplitude

trough

crest

Properties of WavesProperties of Waves

All electromagnetic waves travel at the same speedThe speed of light: 300,000,000 m/s

Wave Speed = wavelength x frequency

Wave Speed = f

(length/second) = (length/cycle) x (cycle/second)

Light as a WaveLight as a Wave

Light waves are characterized by a wavelength

and a frequency f

c = 300,000 km/s = 3108 m/s

ll

Electromagnetic WavesElectromagnetic Waves

Light as a WaveLight as a WaveWavelengths of light are measured in units of

nanometers (nm) or Ångström (Å):1 nm = 10-9 m

1 Å = 10-10 m = 0.1 nm

Visible light has wavelengths between 4000 Å and 7000 Å

(400 nm – 700 nm).

The Electromagnetic SpectrumThe Electromagnetic Spectrum

Need satellites to observe

Wavelength

Frequency

High flying air planes

or satellites

Wavelengths and ColorsWavelengths and Colors

Different colors of visible light correspond to different wavelengths.

Visible Light (VIS)

700 to 400 nm

Our eyes are sensitive to this region of the spectrum

Red-Orange-Yellow-Green-Blue-Indigo-Violet

In other words, In other words, waves with waves with

shorter shorter wavelengths wavelengths

(or higher (or higher frequency) have frequency) have higher energyhigher energy

Light as ParticlesLight as Particles

• Light can also behave like a stream of particles, called photons

• A photon has a specific energy E, • Energy is proportional to frequency and inversely

proportional to wavelength

E = hf

h = 6.626x10-34 J*s is the Planck constant.

The energy of a photon does not depend on the intensity of the

light!!!

Solar Radiation

The Source for 99.9% of Earth’s

Energy

Solar SpectrumSolar Spectrum

The sun emits radiation at all wavelengths

Most of its energy is in the IR-VIS-UV

portions of the spectrum

~50% of the energy is in the visible region

~40% in the near-IR ~10% in the UV

Wavelength (m)

RADIO WAVESRADIO WAVES Have the Have the longestlongest wavelengths and wavelengths and

lowest lowest frequencies of all the electromagnetic waves.frequencies of all the electromagnetic waves. A radio picks up radio waves through A radio picks up radio waves through

an antenna and converts it to an antenna and converts it to sound waves.sound waves.

Each radio station in an area broadcasts Each radio station in an area broadcasts at a different frequency. # on radio at a different frequency. # on radio dial tells frequency.dial tells frequency.

MRI MRI (MAGNETIC RESONACE IMAGING)(MAGNETIC RESONACE IMAGING)

Uses radio waves with a Uses radio waves with a magnet to create an imagemagnet to create an image

MICROWAVESMICROWAVES MicrowavesMicrowaves—have the shortest wavelengths —have the shortest wavelengths

and the highest frequency of the and the highest frequency of the radio waves.radio waves. Used in microwave ovens.Used in microwave ovens.

• Waves transfer energy to the water in the food causing Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the them to vibrate which in turn transfers energy in the form of heat to the food.form of heat to the food.

Used by Used by cell phones and pagers.cell phones and pagers. RADARRADAR ( (RaRadio dio DDetection etection aand nd RRanging)anging)

• Used to find the speed of an object by sending out radio Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.waves and measuring the time it takes them to return.

INFRARED RAYSINFRARED RAYS InfraredInfrared= below red= below red Shorter wavelength and higher Shorter wavelength and higher

frequency than microwaves.frequency than microwaves. You can feel the longest ones You can feel the longest ones

as warmth on your skinas warmth on your skin Heat lamps give off infrared Heat lamps give off infrared

waves.waves. Warm objects give off more Warm objects give off more

heat energy than cool objects.heat energy than cool objects. ThermogramThermogram—a picture that —a picture that

shows regions of different shows regions of different temperatures in the body. temperatures in the body. Temperatures are calculated by Temperatures are calculated by the amount of infrared radiation the amount of infrared radiation given off. Therefore people given off. Therefore people give off infrared rays.give off infrared rays.

VISIBLE LIGHTVISIBLE LIGHT Shorter wavelength and higher frequency than infrared rays.Shorter wavelength and higher frequency than infrared rays. Electromagnetic waves we Electromagnetic waves we can see.can see. Longest wavelength= red lightLongest wavelength= red light Shortest wavelength= violet (purple) lightShortest wavelength= violet (purple) light When light enters a new medium it bends (refracts). Each When light enters a new medium it bends (refracts). Each

wavelength bends a different amount allowing white light to wavelength bends a different amount allowing white light to separate into it’s various colors separate into it’s various colors ROYGBIV.ROYGBIV.

ULTRAVIOLET RAYSULTRAVIOLET RAYS Shorter wavelength and higher frequency than Shorter wavelength and higher frequency than

visible lightvisible light Carry Carry more energymore energy than visible light than visible light Used to Used to kill bacteria.kill bacteria. (Sterilization of equipment) (Sterilization of equipment) Causes your skin to produce Causes your skin to produce vitamin Dvitamin D (good for (good for

teeth and bones)teeth and bones) Too much can cause skin cancer. Too much can cause skin cancer. Use sun block to protect against (UV rays)Use sun block to protect against (UV rays)

X- RAYSX- RAYS Shorter wavelength and higher frequency Shorter wavelength and higher frequency

than UV-raysthan UV-rays Carry a great amount of energyCarry a great amount of energy Can penetrate most matter.Can penetrate most matter. Bones and teethBones and teeth absorbabsorb x-rays. (The light x-rays. (The light

part of an x-ray image indicates a place part of an x-ray image indicates a place where the x-ray was absorbed)where the x-ray was absorbed)

Too much exposure Too much exposure can cause cancercan cause cancer (lead vest at dentist protects organs (lead vest at dentist protects organs

from unnecessary exposure)from unnecessary exposure)

Used by Used by engineersengineers to check for to check for tiny cracks in structures.tiny cracks in structures.

The rays pass through the cracks The rays pass through the cracks and the cracks appear dark on film.and the cracks appear dark on film.

GAMMA RAYSGAMMA RAYS Shorter wavelength and higher Shorter wavelength and higher

frequency than X-raysfrequency than X-rays Carry the Carry the greatest amount of energygreatest amount of energy

and penetrate the most.and penetrate the most. Used in Used in radiation treatmentradiation treatment to kill to kill

cancer cells.cancer cells. Can be very harmful if not used Can be very harmful if not used

correctly.correctly.

SUMMARYSUMMARY All electromagnetic wavesAll electromagnetic waves travel at the travel at the

same speed. (300,000,000 meters/second same speed. (300,000,000 meters/second in a vacuum.in a vacuum.

They all have different They all have different wavelengthwavelength and and different different frequencies.frequencies. Long wavelength-Long wavelength-lowest frequencylowest frequency Short wavelengthShort wavelength highest frequency highest frequency The higher the frequency the The higher the frequency the higher the higher the

energy.energy.