An Introduction to: Light

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Verity Wells
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1 An Introduction to: Light Created by Anna Opitz July 2007

2 Why is light important? Light allows us to see. Light carries information from our surroundings to our eyes and brain. Light enables us to communicate and have contact with the world around us. Image: Eye Chart Image: Times Square, NY

3 How do we use light in our everyday lives? Photo: Sunglasses Photo: Camera Photo: iphone and ipod Photo: Microscope DVD s Telecommunications Television Lighting LCD (Liquid Crystal Display) Astronomy Microscopy Sunglasses Cameras Photosynthesis

4 What is light? In the early 1900 s, scientists had two different models for the behavior of light: 1. A model where light acts as a particle 2. A model where light acts as a wave Particle Wave So, which model is correct? BOTH Light can behave as a particle and a wave at the SAME TIME!

5 Image: Water Waves Waves A wave is something as simple as the ripples from tossing a rock into water or doing the wave at a football game. Image: Water Wave Energy is transferred in a wave, but the medium through which the wave travels does not move.

Light as a Wave Image: Light Wave Image: Light Wave Light is

the result of the meeting of electric and Image:

of 299,792,458 m / s IMPORTANT DIFFERENCE: Unlike other types

6 Light as a Wave Image: Light Wave Image: Light Wave Light is considered an electromagnetic wave Electromagnetic waves are the result of the meeting of electric and Image: Electromagnetic wave magnetic fields Light travels at a speed of 299,792,458 m / s IMPORTANT DIFFERENCE: Unlike other types of waves, electromagnetic waves DO NOT require a medium to travel through!

7 Properties of Waves: Amplitude: half the height of the wave Frequency: measure of number of waves that pass a given point in a given amount of time Wavelength: distance between two identical points on the wave Speed: how fast the wave travels, given by the wavelength times the frequency, or v=λf

8 Focus On: Wavelength When studying waves, the wavelength tells us a lot of information about the wave. Remember! The wavelength is the distance between two identical points on the wave The wavelength (λ) of a wave is given by the formula: λ= v f Where: v= velocity of wave f= frequency of wave It is important to study the wavelength of light, because it tells us about the color of light

9 The Color of Light Light waves have different wavelengths and these wavelengths correspond to colors in the visible light spectrum The colors we see are actually light waves at different wavelengths Each color has a specific wavelength at which it is visible to the human eye

10 Red light has the longest wavelength at about 700 nanometers, while violet light has the shortest wavelength at about 400 nanometers White light is all of the different color waves seen together

is given by: E=hf E- Energy h- Planck s constant f- frequency Higher frequencies

11 Light as a Particle Image: Photons Light is made up of particles called photons Photons are tiny packets of energy The energy of a photon is dependent upon it s frequency and is given by: E=hf E- Energy h- Planck s constant f- frequency Higher frequencies correspond to higher energy photons and lower frequencies to lower energy photons Image: Photon

incandescence (thermal radiation due to temperature) Light

illuminated by the movement of electrons in a semi-conductor

12 How do we create and control light? Light bulbs are a source of artificial light resulting from incandescence (thermal radiation due to temperature) Light Emitting Diodes, or LEDs, are tiny light bulbs that are illuminated by the movement of electrons in a semi-conductor material Lasers produce light beams at one specific wavelength (one color), that are very strong and concentrated

pattern of real images on light sensitive

the colors that make up a particular light

13 How do we measure and study light? Light enters the eyes, where impulses are transmitted to the brain, and the brain identifies light Cameras record the light pattern of real images on light sensitive material Spectrometers obtain a spectrum of the colors that make up a particular light Light detectors convert light power into electrical power

14 Why is it important to study light? Image: Fiber Optics Image: DVD Image: CD The study of light is called Optics Leads to the development of products applied in modern technologies, such as; DVDs, CDs, fiber optics

15 What are some applications of light? Medical: X-rays, laser eye surgery Media: television, movies, paintings, CDs Industrial: laser cutting, photolithography, communications Scientific: spectroscopy, forensics, identification of elements Image: X-Ray Image: Laser cutting Image: Television Image: Forensic laser use

16 What is Spectroscopy? Spectroscopy studies the way an object s light divides into it s component colors The image shown to the left are the spectra patterns for H, He, N, Ne, Ar, and Hg gases Through analysis of an object s light, physical properties such as; luminosity, mass, temperature, and composition can be determined Data is obtained using a spectrometer, which works like a prism

nano scale, advance cyber cryptography, and study light on the nano scale.

17 Nano-sized Light Sources What is the future of light? Nano-sized light sources would make it possible to look inside individual cells, bio-image on the nano scale, advance cyber cryptography, and study light on the nano scale. Image: Nano-wire Light Quantum Computers Quantum Computers would be able to store more information and also perform much faster than the computers we use today. Image: Quantum Chip

The Structure of the Atom

CHAPTER 5 The Structure of the Atom 5.4 Light and Spectroscopy 460 370 BC 1808 1870 1897 1910 1925 Today Democritus Atomism Dalton Modern atomic theory Crookes Cathode rays Thomson Discovery of the electron