### Table of Contents

# PH315: The Physics of Contemporary Challenges

- Instructor: (Winter 2017) Prof. Ethan Minot, Office: Weniger 417
- TA: (Winter 2017) Dr. Paul Emigh, Office: Weniger 491
- Textbook: See course information
- Class Meetings: MWF 12.00 - 12.50pm, Weniger 212
- Homework help session: Thursday 10.00 - 12.00noon in Weniger 334 “the wormhole”

## Week 1

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 1/9 | SNOW DAY | ||

Wed 1/11 | Physical Reasoning | Intro to class. Order of magnitude estimates: Example, hydroelectric capacity of Columbia River. In-class exercise: Roof-top hydro. Day 1 screen/audio capture. day1_2017.pdf | hw1 |

Fri 1/13 | Physical Reasoning | David MacKay's free book has many more order of magnitude estimates related to renewable energy. Simplified models: Example, the energy consumed when driving a car. Interpreting graphs: Example, solar intensity at Humboldt State University. Day 2 screen/audio capture, day_2_2017.pdf | hw1 due |

## Week 2

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 1/16 | MLK HOLIDAY | hw2 | |

Wed 1/18 | Physical reasoning | Definition of power. Numerical integration: Example, solar intensity at Humboldt State University. Numerical differentiation: Example, energy stored in the battery of an electric car. Day 3 screen/audio capture, day_3_2017.pdf | - |

Fri 1/20 | Thermal Physics | Temperature is a way of quantifying a material's internal energy per atom (or molecule). The relationship is different for different materials. Practice problem: Internal energy of a cup of water. The equipartition theorem. How many degrees of freedom? Day 4 screen/audio capture, day_4_2017corrected.pdf | HW2 solutions |

## Week 3

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 1/23 | Thermal Physics | Define specific heat capacity. Count degrees of freedom for 2 point-like particle connected by a spring. Apply equipartition theorem to some different gases, solids and liquids. The role of quantum mechanics in reducing the number of degrees of freedom that store thermal energy. Intro to heat transport. Day 5 screen/audio capture day_5_2017.pdf | hw3 |

Wed 1/25 | Thermal Physics | Define heat and heat flux. Fourier's law of heat transport. Second order partial differential equation to describe Monday's kinesthetic activity. Heat flux through the wall of a building. Intro to PV diagrams using a ballon, liquid nitrogen and a piston. Day 6 screen/audio capture, day_6_2017.pdf | Reading Assignment: Gas Processes |

Fri 1/27 | Thermal Physics | Calculating the efficiency of an engine that uses expansion/contraction of a working gas to push a piston. Day 7 screen/audio capture, ideal gas law derived from microscopic picture, day_7_2017.pdf | HW3 solutions |

## Week 4

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 1/30 | Thermal Physics | Examples of heat engines in technology. Introduction to heat pumps. Isothermal expansion versus adiabatic expansion. PhET simulation. Performance of an ideal heat pump. day_8_2017.pdf, Day 8 screen/audio capture | hw4 |

Wed 2/1 | Light-Matter Interactions | Light is an electromagnetic wave. Relationship between wavelength, frequency and speed of light. Some variables are easier to measure than others. Interference patterns as a technique to measure wavelength. Example, wavelengths in from hydrogen gas lamp. day_9.pdf, Day 9 screen/audio capture | - |

Fri 2/3 | Lab | From 2-slit interference to 10-slit interference day_10_2017.pdf. Measuring the Planck constant Part 1 | HW4 Solutions |

## Week 5

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 2/6 | Lab | Measuring the Planck constant Part 2 | hw5 |

Wed 2/8 | Light-Matter Interactions | Guidance on the lab write up. Intro to the wave properties of light: the oscillating electric and magnetic field and energy flux. Intro to the particle properties of light: energy arrives at detector in discrete packets. Energy lost by each each electron passing through an LED is transferred to one photon. Day 12 screen/audio capture, day_12_2017v2.pdf, practice_midterm_2017.pdf | - |

Fri 2/10 | Review | LED intensity (exercise from last class). Review of what the midterm covers. Day 13 screen/audio capture | - |

## Week 6

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 2/13 | Mid-term exam | ||

Wed 2/15 | Light-matter Interactions | Reflections on midterm, hw4, and hw5. Preview of rest of course. The Correspondence Principle for quantum mechanics. Charged ball and spring model for CO2. Day 14 screen/audio capture, graphs_handout.pdf, day_14_2017.pdf | Reading assignment: Greenhouse gases |

Fri 2/17 | Light-matter interactions | How electric field distorts the geometry of a CO2 molecule. Calculation of a natural frequency (resonance frequency). Wavelengths of light that excite resonant vibrations of CO2. Physical mechanism for light scattering. Definition and calculation of the optical cross section. Day 15 screen/audio capture, day_15_2017.pdf, stretching_molecules.pdf | - |

## Week 7

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 2/20 | Thermal Radiation | Relationship between thermal radiation and contemporary challenges. Physical mechanism for the emission of thermal radiation. High frequency vibrations are suppressed by QM, therefore, high frequency light waves are not emitted. Approximate temperature dependence of thermal radiation. Day 16 screen/audio capture, day_16_2017.pdf | hw6 |

Wed 2/22 | Blackbody Spectrum | Start class with blackbody_spectrum_worksheet.pdf, students work in pairs. Discuss answers. Peak wavelength corresponds to photon energy 5kT. day_17_2017.pdf | - |

Fri 2/24 | Blackbody Spectrum | Derivation of blackbody spectrum formula. The QM-corrected version of equipartition theorem (Bose-Einstein statistics). Relationship to Correspondence Principe and excercise with Taylor series expansion. Shortcomings of the approximate model from Day 16. Assuming light trapped in a cavity and cavity modes in thermal equilibrium. Definition of spectral intensity (as opposed to intensity). Day 18 screen/audio capture, hw6_q6_hint.pdf, day_18_2017.pdf, | HW6 solutions |

## Week 8

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 2/27 | Earth's climate | How the blackbody spectrum got its name. Hint for HW7 (u substitution). Sun and Earth both emit radiation with approximate blackbody spectra. Use Stefan-Boltzmann law to estimate the intensity of sunlight incident on Earth's upper atmosphere. Calculate power delivered to Earth. Discuss albedo. Estimate Earth's temperature (without considering the atmosphere). Day 19 screen/audio capture, day_19_2017.pdf | hw7 |

Wed 3/1 | Earth's climate | Exercise: Find the intensity of sunlight incident on Mars's upper atmosphere. List the shortcomings of the bare Earth climate model. Introduce the “one layer” atmosphere model as a simplified model of greenhouse effect. Estimate Earth's temperature. Day 20 screen/audio capture, day_20.pdf | Reading assignment |

Fri 3/3 | Earth's climate | HW7 hint: Calculating steady state temperature and estimating dT/dt when system is not in steady state. Introduce a more sophisticated greenhouse model, multi-layer and multi-wavelength. Discuss positive feedback and negative feedback on Earth's temperature. Discuss experimental uncertainty related to measuring Earth's temperature and sea level. Day 21 screen/audio capture, day_21_2017.pdf, climate_change_graphs.pdf | HW7 solutions |

## Week 9

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 3/6 | Wave nature of particles | In-class activity: Use diffraction gratings to observe the spectra from incandescent lamps and mercury vapor lamps. Discrete energies of electron in mercury atom motivates a model that treats electrons as waves. de Broglie wavelength. Demonstration of electron diffraction and interference effects. Similarities between electron waves and other wave. Demonstration of discrete resonant frequencies of an oscillating string. day_22_demonstrations.pdf, class_notes_from_paul.pdf | |

Wed 3/8 | Wave nature of particles | Wave equations (partial differential equations) with boundary conditions have a discrete set of solutions. Representing the set of solutions on a frequency level diagram. Solutions to Schrodinger equation represented on an energy level diagram. Photon absorption or emission from the electron of a hydrogen atom. day_23_2017.pdf | - |

Fri 3/10 | Wave nature of particles | Sound waves in a bugle are another example of discrete solutions to a partial differential equation that has boundary conditions. Use a spectrogram to visualize the frequency level diagram for a bugle. Return to energy level diagrams of hydrogen. Define the eV energy unit. Converting from photon energy (in eV) to wavelength (in nm). The four visible wavelengths emitted by hydrogen. Mercury vapor lamp works by accelerating ionized atoms in an electric field and using atom-atom collisions to excite transitions between energy levels. Day 24 screen/audio capture, day_24_2017.pdf, mercury_lamp.pdf, | - |

## Week 10

Date | Topic | What was covered | Assignments |
---|---|---|---|

Mon 3/13 | Energy levels in atoms and molecules | Stimulated emission and basic considerations for designing a laser. The energy levels that are occupied by the last 6 electrons in the dye molecule cyanine. The Pauli exclusion principle. Day 25 screen/audio capture, day_25_2017.pdf | Term-paper due |

Wed 3/15 | Energy levels in molecules and solids | Estimate the absorption spectrum of a chlorophyll molecule. Explain why leaves are green. Discuss the charge separation process that happens after light absorption. Electron waves in solids. Bands of energy levels. Band gaps. Metals have a partially filled band. Semiconductor and insulators do not. Introduce silicon photovoltaics. Day 26 screen/audio capture, day_26_2017.pdf | - |

Fri 3/17 | Photovoltaics | Calculating the efficiency of a photovoltaic device. Max efficiency for the solar spectrum is ~30%, requires band gap ~1.4 eV. Day 27 screen/audio capture, day_27_2017.pdf, "HW8" practice questions - not graded. | HW8 solutions |

## Finals week

Thur 3/23 6pm - 8pm | Final exam |