Unit2Day1 VandenBout Wednesday September 18 2013 4 13 PM Vanden Bout LaBrake Crawford CH301 Why should I wear sunscreen ELECTROMAGNETIC RADIATION UNIT 2 Day 1 CH301 Vanden Bout LaBrake Fall 2013 Important Information EXAM GRADES WILL BE POSTED By SATURDAY MORNING LM12 and LM13 due Tue 9AM HW4 due Tue 9AM LAUDE LM LECTURE 1 NO POINTs EXTRA CH301 Vanden Bout LaBrake Spring 2013 Unit2Day1 VandenBout Page 1 What are we going to learn today Electromagnetic Radiation Understand light as an electromagnetic wave Understand the relationship between frequency wavelength and the speed of light Light as Energy Understand how light interacts with electrons Explain the basic principles of the photoelectric effect Recognize that light is related to frequency Explain the concept of a photon CH301 Vanden Bout LaBrake Fall 2013 What is Light Chemists use the word light to generally refer to electromagnetic radiation CH301 Vanden Bout LaBrake Fall 2013 Electro Magnetic Wave Oscillating Electric and Magnetic Field Unit2Day1 VandenBout Page 2 Oscillating Electric and Magnetic Field CH301 Vanden Bout LaBrake Fall 2013 What is an Electric Field Electric Fields surround charged particles and time varying magnetic fields Cause charge particles to feel a force A fairly simply field exists between to plates of opposite electrical charge CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 3 POLLING CLICKER QUESTION 1 e If I place an electron between these two plates it will feel a force in what direction A B C D E Left Right Up Down None CH301 Vanden Bout LaBrake Fall 2013 E Field from Light The field is oscillating http www enzim hu szia cddemo edemo2 htm CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 4 POLLING CLICKER QUESTION 2 If I place an electron in the presence of an oscillating electric field the electron will e A B C D E Left Right Up Down Oscillate CH301 Vanden Bout LaBrake Fall 2013 Describing the wave Distance between the peaks is the wavelength It really is a distance If I am in one place how often do the peaks pass It depends on the speed and the wavelength CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 5 3 key parameters for a wave Wavelength Distance between peaks Speed of light The speed of light in a vacuum is constant All light waves travel at the same speed c 2 998 x 108 m s 1 Frequency The time it takes between two peaks n c distance s 1 distance s 1 Hz CH301 Vanden Bout LaBrake Fall 2013 Key Relationship You can now do most of HW 04 CH301 Vanden Bout LaBrake Fall 2013 Wavelengths of Light We typically classify light by wavelength But frequency works equally well Unit2Day1 VandenBout Page 6 We typically classify light by wavelength But frequency works equally well CH301 Vanden Bout LaBrake Fall 2013 POLLING CLICKER QUESTION 3 Light and Electrons Everything has electrons In metals those electrons can move conductor What will happen if we shine light on a piece of metal A The electrons will do nothing B The electrons will oscillate back and forth C The electrons will feel a force but not move D The electrons will turn into protons CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 7 POLLING CLICKER QUESTION 4 Light and Electrons What will happen if we shine brighter light Bright light Bigger Amplitude CH301 Vanden Bout LaBrake Fall 2013 POLLING CLICKER QUESTION 4 Light and Electrons What will happen if we shine brighter light Bright light Bigger Amplitude A they will oscillate faster B they will oscillate with a bigger amplitude C more of them will oscillate D more of them will oscillate faster CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 8 Let s Do an Experiment Light Metal Virtual Demo Use one laptop per group and work together on the activity http phet colorado edu en simulation photoelectric CH301 Vanden Bout LaBrake Fall 2013 Let s Do a Virtual Experiment Using Photoelectric Effect Simulator CH301 Vanden Bout LaBrake Fall 2013 Let s Do an Experiment Summarize results of experiment Unit2Day1 VandenBout Page 9 Summarize results of experiment CH301 Vanden Bout LaBrake Fall 2013 Threshold Frequency CH301 Vanden Bout LaBrake Fall 2013 A whole new idea about Energy The energy of the light is proportional to the frequency The energy appears to come in packets or photons One photon interacts with one electron Unit2Day1 VandenBout Page 10 The energy appears to come in packets or photons One photon interacts with one electron h is Planck s Constant CH301 Vanden Bout LaBrake Fall 2013 The work function is the minimum E need to eject and electron It is different for different metals CH301 Vanden Bout LaBrake Fall 2013 POLLING CLICKER QUESTION 5 If an electron is ejected from the metal surface where does the energy of the photon go a Over coming potential energy holding e in metal b Into the KE of the electron c Carried away with reflected light d Heat e Both a b CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 11 CLASSIC ENERGY DIAGRAM and POTENTIAL ENERGY WELL CH301 Vanden Bout LaBrake Fall 2013 POLLING CLICKER QUESTION 6 Which of these types of light has the highest energy photons A B C D E Green Light 540 nm or 5 4 x 10 7 m Red Light 650 nm or 6 5 x 10 7 m Radio waves 100 m X rays 0 5 nm or 5 x 10 10 m Infrared 3 mm or 3 x 10 6 m CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 12 Quick Review of DNA CH301 Vanden Bout LaBrake Fall 2013 Why Should I wear Sunscreen TYPES of DNA DAMAGE CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 13 Why Should you wear Sunscreen AVOBENZONE common active ingredient UVmax 357 nm Zinc Oxide reflects UV light CH301 Vanden Bout LaBrake Fall 2013 What Did We Learn Today Light is a wave with a frequency speed and wavelength The energy of light is related to the frequency in a way that light seems like a particle one photon affects one electron THIS ALLOWS US TO USE LIGHT TO PROBE THE ENERGY OF ELECTRONS IN MATTER CH301 Vanden Bout LaBrake Fall 2013 Unit2Day1 VandenBout Page 14 Learning Outcomes Understand and perform quantitative calculations based on the relationship between wavelength energy and the speed of light Define wavelength frequency and energy of a photon Understand identify and rank the different types of light radiation Describe the photoelectric effect and relate the energy of a photon the work function and the kinetic energy of the electrons and describe the effect of the intensity and the energy of the light Students should understand atomic
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