Warm Up

1. Warm Up • What is a continuous, uninterrupted range of electromagnetic radiation called? • Give 5 examples of divisions within the E/M range. • Tell some of the ways that these divisions are used by people. • What is frequency and what is its relationship to time? • What does the expression “the dual nature of light” mean?

2. Warm Up What is light? What are some of the common characteristics of light? What are the two accepted models of light? Where does light come from? How does the structure of the atom effect light?

3. Warm Up • Who discovered that light was composed of different colors? • What are the colors of the visible light spectrum? • How does a prism separate light? • Light cannot slow down, but it can change…?

4. Warm Up • Explain the Doppler Effect! • What is the blue-shift? • What is the red shift? • How does Doppler weather forecasting work? • A wave generator makes a new wave every 0.1 seconds. What is the frequency of the wave? • The frequency of a jump rope is 2 hertz. How long does it take to make one wave?

5. Warm Up • How is light like a wave? • Give an example of light acting like a wave. • How is light like a particle? • Give an example of light acting like a particle.

6. The Origins of Light By Ken Journigan

7. What is Light • Light is one of the many forms of electromagnetic radiation (EMR). What is EMR exactly? • EMR is The way energy gets from one place to another without any physical connection. What are some examples of EMR that I might know? Light, radio, microwaves, x-rays and gamma waves are all examples of EMR. Light energy comes in a variety of forms and consists of waves that range from large to small.

8. These waves form a continuum called a spectrum

9. Divisions of the E/M spectrum What determines the type of Electromagnetic radiation is the length of the wave that forms it. Some of the types you are familiar with are the radio, microwave and x-ray spectra.

10. Uses Thermal imaging Communication Microwave ovens (biological) Infrared remote controls Medical imaging (X-rays and MRI) Radio transmission Communication Cell phones (undersea) Oncology Seeing Light Tanning

11. Divisions of the visible Spectrum Another division of the E/M spectrum that we all know is the visible light spectrum. The portion of the E/M spectrum that we can actually see is quite small but very important. WE SEE IT IN RAINBOWS AND SOAP BUBBLES.

12. So, what you’re saying is….. Electromagnetic Energy can get from place to place even when these places aren’t physically connected. This energy travels using waves. These waves range continually from very big (long) ones to very small (short) ones. Some of these we can see, but most we cannot. YES, THAT”S EXACTLY WHAT I’M SAYING

13. Common characteristics of waves: Parts of Waves The distance from one crest of a wave to the next crest is known as its wavelength. All waves have a wavelength (l). THE LOWER PART OF THE WAVE IS CALLED THE TROUGH.

14. Common characteristics of waves: Parts of Waves (continued) Frequency: Imagine that you are watching these waves zoom past. Pretend that you can count how many of these invisible waves pass you each second. You now know the waves frequency. Frequency is measured in hertz or cycles per second. Time: Now pretend that you can tell the time in between each peak. You write them down as the frequency increases and decrease until you suddenly notice…

15. Frequency and Time are Related Yes, It’s sad but true that frequency (f) and time (t) are inversely related. This means that…. f = 1/t and t = 1/f As frequency increase, the time between waves decreases and conversely… As the time between waves increases, the frequency decreases.

16. Doppler Effect • Applet Doppler Effect • http://www.lon-capa.org/~mmp/applist/doppler/d.htm

17. Red Shift • As a luminous body travels away from you, its light is stretched or elongated. This (Doppler) effect shifts the light toward the red end of the spectrum. This phenomenon is known as the red shift.

18. Blue Shift • As a luminous body travels toward you, its light is compressed. This (Doppler) effect shifts the light toward the blue end of the spectrum. This phenomenon is known as the blue shift

19. The Wave Model of Light Refraction is the bending of light. Light bends, as do all waves, when they pass from something thick to something thin (like from air into water). Have you ever noticed your straw in an iced tea glass?

20. The Wave Model of Light (cont’d) Prisms separate light into their constituent colors (Roy G. Biv). Light slows down as it passes through the more dense prism. Different frequencies (colors of light) are slowed down by different amounts. This is why a prism spreads out light into its spectrum of colors.

21. The Particle Model of Light Reflection: Like a small BB or rubber ball hitting a wall, light bounces off (or reflects) off of objects. In this way light is characteristic of a particle.

22. Two Models of Light? What ‘s Up with That? That’s Right! There are two models of the nature of light. Which one is right? They both are! Which model do you use? The one that best suites your purpose. Whose idea was the wave model of light? Sir Isaac Newton (around 1650). Whose idea was the particle model of light? Albert Einstein (around 1915).

23. Where Does Light Come From? The electrons within atoms can absorb energy from passing waves (if it is the right frequency). The electrons then move outward from their “ground” state to an excited state. The electron will later return to its ground state. When it does, it releases this stored energy in the form of a photon. A photon is a tiny packet of light. This process is known as electron emission. Einstein proposed the photon is his particle model of light.

24. Electron Absorption Demonstration, Absorption and Emission of Radiation by an Atom

25. Warm Up • Diagram the three ways images form in reflective surfaces. • What are the two models of light? Explain each! Whose ideas were each model?

26. Quantum Mechanics The science that studies the change in states that electrons experience is called Quantum physics. Electrons can only exist in orbits that are specific distances from their nuclei. This is why electrons can only absorb energy of certain wavelengths. This is also why each element emits photons of only a certain wavelength as well. Each element has a characteristic “fingerprint” of light that it emits.

27. The Three Types of Spectra Continuous: A spectrum of visible light from red to violet without interruption. Emission: A spectrum composed of only light emitted from particular elements (atoms). Absorption: an otherwise continuous spectrum of light missing the portion of the spectrum absorbed by electrons.

28. The Origins of Spectra Continuous spectrum: originates from the separation of white light into its constituent colors. Emission Spectra: originate from photons generated from electrons returning to their ground states. Absorption spectra: are the result of a continuous spectrum passing through cool gas. The gas selectively absorbs the energy so that its electrons can move to an excited state.

29. Summary of Light Light has two models: one says light acts like a wave and one says light acts like a particle. Both are correct and you use the models that best suites your needs. The Newtonian wave model says light comes in a continuous range from long to short called a spectrum. This electromagnetic spectrum is divided up into sections featuring visible light, radio waves, microwaves, x-rays, ultraviolet waves and infrared waves. Light waves bend when they pass into mediums of different mediums

30. Summary of Light (cont’d) Einstein’s particle model says that light is released in little packets called photons. The photons act like particles and bounce off objects into which they collide. All waves have a height (amplitude) and a frequency (f) and a wavelength (l). The frequency of a wave is how many waves pass a fixed point in one second. Frequency is measured in cycles per second or hertz. Frequency and time are inversely related.

31. Summary of Light (cont’d) Bohr says that the electrons that orbit around a nucleus normally exist in an unexcited, ground state. However, if they encounter the proper wavelength of energy, the electrons will absorb that energy by shifting their positions to an outer orbit. This is known as absorption. This excited state is only temporary and the electron will eventually release this energy and return to its ground state. The electron releases this energy in the form of a photon.

32. For additional information Print Resources: • Berg, R., DeFronzo, R., Eisenkraft, A., Rheam, H., Roeder, J., Rourke, P., Weathers, L..et al. (2000). Active physics/communication. New York: It’s About Time, Inc. • Forget, M. (2004). Max reading teaching with reading and writing: classroom activities for helping students learn new subject matter while acquiring literacy skills. Victoria, Canada: Traford Publishing. • Arny, T. (2006). Explorations: Introduction to Astronomy (4th ed.). New York: McGraw-Hill. • Comins, N.F. (2004). Discovering the Essential Universe (2nd ed.). New York: W.H. Freeman.

33. For additional information On-line Resources: http://online.nmit.vic.edu.au/courses/electronic/vbb221/tut1_1_2.htm http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html http://www.geo.mtu.edu/rs/back/spectrum/ http://www.physicsclassroom.com/Class/light/U12L1a.html http://csep10.phys.utk.edu/astr162/lect/light/absorption.html http://hyperphysics.phy-astr.gsu.edu/hbase/mod5.html http://www.physics.uoguelph.ca/applets/Intro_physics/kisalev/java/atomphoton/ http://www.jracademy.com/~jtucek/science/what.html http://www.en.wikipedia.org/wiki/Refraction

34. Lenses • http://www.shermanlab.com/science/physics/optics/ThinLens.php • http://www.shermanlab.com/science/physics/optics/SphericalMirror.php

35. Key Questions for Next Class What happens to the light we see from stars before it reaches our eyes? Does the Earth’s atmosphere change the light that we see? Do we really need telescopes in space? Please ponder these questions between now and then!