Exam #1 Approaching 1 st Exam will be in four days (Friday, Sept. 18) – Chapters closed book/notes exam 40 questions, multiple choice, no calculators needed, bring a #2 pencil with an eraser If it’s in the book but not in the notes, it will NOT be on the test. Focus on concepts, not details. Reviews at end of each chapters a good study guide, but do NOT represent everything you need to know for the exam. Notes available from first link on Blackboard (Updated syllabus) – be sure to scroll down to correct date – if you don’t see the notes, try hitting the reload button of your browser

Waves  A wave is a pattern of motion that can carry energy without carrying matter along with it

Properties of Waves  Wavelength is the distance between two wave peaks (unit: meter, for example - denoted )  Frequency is the number of times per second that a wave vibrates up and down (unit: Hertz =1/seconds) - denoted  ) wavelength * frequency = wave speed  Wavelength is the distance between two wave peaks (unit: meter, for example - denoted )  Frequency is the number of times per second that a wave vibrates up and down (unit: Hertz =1/seconds) - denoted  ) wavelength * frequency = wave speed For light: *  = c (speed of light)

Anatomy of a Wave

Wavelength and Frequency of Light Wavelength * frequency = speed of light = constant If you change the wavelength/frequency of light, you change the type of light (X-ray, ultraviolet, visible, infrared, etc.) Wavelength * frequency = speed of light = constant If you change the wavelength/frequency of light, you change the type of light (X-ray, ultraviolet, visible, infrared, etc.) Longer wavelength, lower frequency Shorter wavelength, higher frequency

Particles of Light  Particles of light are called photons, which are massless.  Despite being a particle, photons have a wavelength and a frequency (and energy and momentum).  The energy of a photon depends on its frequency.  Particles of light are called photons, which are massless.  Despite being a particle, photons have a wavelength and a frequency (and energy and momentum).  The energy of a photon depends on its frequency.

Wavelength, Frequency, and Energy E = h *  = h *c / = photon energy h = Planck’s constant (universal constant) As a reminder,  is a frequency (measured in Hz) and is a wavelength (measured in meters) E = h *  = h *c / = photon energy h = Planck’s constant (universal constant) As a reminder,  is a frequency (measured in Hz) and is a wavelength (measured in meters)

The electromagnetic spectrum Gamma rays X-rays Ultraviolet Optical Infrared Microwave Radio EnergyEnergy WavelengthWavelength More wave-like More particle-like Each part of EM spectrum interacts differently with matter. FrequencyFrequency

The higher the photon energy A)The longer its wavelength. B)The shorter its wavelength. C) Photon energy is independent of wavelength. A)The longer its wavelength. B)The shorter its wavelength. C) Photon energy is independent of wavelength.

The higher the photon energy A)The longer its wavelength. B)The shorter its wavelength. C) Photon energy is independent of wavelength. E = h * , but  = c /  so  h * c / So if E goes up, wavelength goes down. A)The longer its wavelength. B)The shorter its wavelength. C) Photon energy is independent of wavelength. E = h * , but  = c /  so  h * c / So if E goes up, wavelength goes down.

Which travels at the higher speed? A) Gamma rays. B) Optical (visible) light. C) Radio waves. D) They all travel the same speed A) Gamma rays. B) Optical (visible) light. C) Radio waves. D) They all travel the same speed

Which travels at the higher speed? A) Gamma rays. B) Optical (visible) light. C) Radio waves. D) They all travel the same speed. They all travel at the same speed of light! A) Gamma rays. B) Optical (visible) light. C) Radio waves. D) They all travel the same speed. They all travel at the same speed of light!

What is the structure of matter? Atoms are composed of protons, neutrons and electrons. Protons carry positive charge in nucleus Neutrons are uncharged and reside in the nucleus too (about same mass as proton) Electrons carry negative charge in electron cloud surrounding nucleus – # electrons = # protons in a neutral atom (very small mass compared to proton) Electron cloud is much bigger (100,000x) than nucleus  atom is nearly all empty space! The atom

Atomic Terminology  Atomic number = # of protons in nucleus  Atomic mass number = # of protons + neutrons  Atomic number = # of protons in nucleus  Atomic mass number = # of protons + neutrons It’s the number of protons that makes an element (hydrogen, helium, carbon, etc.) what it is….. (Hydrogen-1)(Helium-4)(Carbon-12)

Atomic Terminology  Isotopes: atoms with the same # of protons but different # of neutrons # of protons determine the chemical properties, not neutrons  above isotopes are all carbon and behave chemically like carbon

More Terminology  Molecules: consist of two or more atoms joined together chemically (H 2 O, CO 2 ) CO 2 – carbon dioxide

Which two of the following are isotopes of each other? A) CO 2 and H 2 O B) Nitrogen-14 and Carbon-14 C) Helium-3 and Helium-4 D) Hydrogen-1 and Helium-4 A) CO 2 and H 2 O B) Nitrogen-14 and Carbon-14 C) Helium-3 and Helium-4 D) Hydrogen-1 and Helium-4

Which two of the following are isotopes of each other? A) CO 2 and H 2 O B) Nitrogen-14 and Carbon-14 C) Helium-3 and Helium-4 D) Hydrogen-1 and Helium-4 Isotopes are always of the same element (in this case, helium). Helium-4 has one more neutron than Helium-3 (both have two protons). A) CO 2 and H 2 O B) Nitrogen-14 and Carbon-14 C) Helium-3 and Helium-4 D) Hydrogen-1 and Helium-4 Isotopes are always of the same element (in this case, helium). Helium-4 has one more neutron than Helium-3 (both have two protons).

What is a spectrum? A spectrum of light is obtained by dispersing it into its constituent wavelengths. Spectra of astrophysical objects tell us about the temperature and chemical composition of the object.

Continuous Spectrum Emission Line SpectrumAbsorption Line Spectrum What are the three basic types of spectra? Spectra of astrophysical objects are usually combinations of these three basic types.

Continuous Spectrum  The spectrum of a common (incandescent) light bulb (or star or any blackbody) spans a wide range of wavelengths (not just optical), without interruption. Continuous light source: Incandescent bulb, star, rock, you, any object with a temperature

Thermal (Blackbody) Radiation  Nearly all large or dense objects emit thermal (or blackbody) radiation, including stars, planets, and you.  An object’s thermal radiation spectrum depends on only one property: its temperature.  (Low-density gas does not emit like a blackbody, but in discrete emission/absorption lines – more on this in a bit)  Nearly all large or dense objects emit thermal (or blackbody) radiation, including stars, planets, and you.  An object’s thermal radiation spectrum depends on only one property: its temperature.  (Low-density gas does not emit like a blackbody, but in discrete emission/absorption lines – more on this in a bit)

Properties of Blackbody (Thermal) Radiation 1.Hotter objects emit photons with a higher average energy – Wien’s Law. 2.Hotter objects emit more light at all wavelengths per unit area – Stefan-Boltzmann’s Law. We say that stars, light bulbs, rock, metal, you, any dense object with a non-zero temperature will emit as a blackbody. Important concept!

Properties of Blackbody (Thermal) Radiation Color of metal poker changes from dull red to red to orange, and then eventually to white as metal heats up  Wien’s Law

You Emit as a Blackbody!  The human body has a temperature of 310 K.  Peak emission happens in the infrared.  Night vision goggles work by detecting the infrared blackbody emission from your body.  The human body has a temperature of 310 K.  Peak emission happens in the infrared.  Night vision goggles work by detecting the infrared blackbody emission from your body. optical infrared

Emission Line Spectrum  A low-density cloud of hot gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines Gaseous nebula

Absorption Line Spectrum A cloud of cold gas between us and a light bulb can absorb/re-direct light of specific wavelengths, leaving dark absorption lines in the spectrum. A cloud of cold gas between us and a light bulb can absorb/re-direct light of specific wavelengths, leaving dark absorption lines in the spectrum.

Electron Energy Level Transitions  In atoms, electrons can only have certain allowed orbits (energy levels) around the nucleus. A larger orbit implies a higher (excited) energy level. Electrons can change orbits only by absorbing/emitting energy (a photon), and can only move from one discrete orbit to another.

Electron Energy Level Transitions Downward electron energy level transitions release a photon at a specific wavelength. Upward energy level transitions occur when a photon (from a background light source) is absorbed by the atom. Leads to an emission line Leads to an absorption line