Points – 538.27 – 69.01 – 6 (12)9.15 – 14 (26)10.08 – 2 (28)10.15 – 6 (34)10.20 – 9 (43)10.29 – 3 (46)11.05 – 1 (47)11.10 – 4 (51)11.12 – 2 (53)11.24 – 3 (56)Lecture #9Light MatterToday1. Nature of Light2. Properties of MatterReadings Chapter 5 (sections 1-3)How do we experience Light?- Warmth (sun)- ColorColors is Light- Light is made up of many different colorso Very hot material emits visible light (sun, wire in light bulb)o Cool light (from a chair) doesn’t emit visible light by itself Absorbs and reflects it- i.e. Red Chair = absorbs blue light, reflects red lightHow do light and matter interact?- Emission - Absorptiono Materials that absorb = opaque- Transmission (allow some to pass through)o Materials that transmit = transparent- Reflection (or redirecting or scattering)o Reflection = bouncing in same general directiono Scattering = more randomRecap- How do we experience light?o Light is a form of energyo Light comes in many colors that combine to form white light- How does light interact with matter?o Matter can emit, absorb, transmit, and reflect (redirect/scatter) lighto Interactions between light and matter determine the appearance of everything we see around us Part 2 What is light?- Light can act either like a wave or like a particle- Particles of light are called photonsWaves- Pebble in the pond analogyo Waves ripple in the pond Consists of trough (water lower than average) and peaks (water higher than average)o Leaf in pond will rise and fall with peaks and troughs but won’t move  waves carry energy outward but do not carry matter along with them- Particle = thing- Wave = pattern revealed by interactions with particlesProperties of Waves- 3 basic properties of waves: wavelength, frequency, and speed- Wavelength o Distance from one peak to the next- Frequencyo Number of times (per sec) that a wave vibrates up and down “cycles per second” often called Hertz (Hz)- Wave Speedo Wave Speed = Wavelength x Frequency Tells us how fast their peaks travel Light: Electromagnetic Waves- A light wave is a vibration of electric and magnetic fieldso Light is an electromagnetic wave Causes electrons to bob up and down – wriggle as a snake as light passed byo A field is used to describe the force an object would feel when in a certain space- Light interacts with charged particles through these electric and magnetic fieldso Light always travels at the speed of light (about 300,000 km per sec) Wavelength x Frequency = Speed of Light (c)o So there is an inverse relationship between Frequency and Wavelength Longer Wavelength = Shorter Frequency Examples- If W is 1cm, F must be 30 GHz- Therefore, if W = .5cm  F would double to 60 GHz- W = .25cm  F = 120 GHzParticles of Light- Particles of Light are called photonso Has properties of both particles and waves- Each photon has a wavelength and a frequency- The energy of a photon depends of its frequency o Directly proportional to its frequencyo E = h x f H is called “Planck’s Constant”Electromagnetic Spectrum- Light we can see = Visible Lighto 400nm – 700nm (Blue  Red)- In order of Short  Long Wavelengthso Gamma rays, X-Rays, UV rays, Visible, Infrared, Radioo High frequency  low frequency (inversely proportional to wavelength)o Large energy per photon  small energy per photon- Infrared Lighto Wavelengths somewhat longer than red lights Lies beyond red in the spectrum I.E. Jupiter- Radio Waveso We hear sound waves from the car radio, not electromagnetic waveso Sometimes given the name microwaves Radar, Microwave ovens Cosmic microwave background  Radio images of Galaxies (Centaurus A)- Ultraviolet (UV) Lighto Just to the left of visible light (violet) Example: The Suno Mostly absorbed by the ozone in the atmosphere o Can cause skin cancer- X-Rayso Very short, very energetic wavelengths (left of UV, right of Gamma)o Can penetrate through tissues, but not bones- Gamma Rayso Most energetic, shortest wavelengthso Extremely Violent eventsRecap: Properties of Light- What is light?o Can behave either like a wave or a particleo A light wave is a vibration of electric and magnetic fieldso Light waves have a wavelength and a frequencyo Photons are particle of light- What is the electromagnetic spectrum?o Human eyes cannot see most forms of lighto The entire range of wavelengths of light is known as the electromagnetic spectrumProperties of MatterWhat to know- What is the structure of matter?- What are the phases of matter?What is the Structure of Matter- Electron (Negative), Protons (Positive – Red), and Neutrons (Neutral – Grey)- Atomic Termso Atomic Number – number of protons in nucleus Number of electrons = number of protonso Atomic Mass – number of protons and neutronso Molecules – consist of two or more atomso Isotopes – Atoms with same number of protons, but different number of neutronsPhases of Matter- Solid, liquid, gas o Phases depend primarily on temperature but are also affected by pressureTemperature- Measures how fast particles (atoms or molecules) moveTemp. Scales- Water Boils around 100 C- Freezes at 0 C- Absolute Zero = -273.15 C- Room Temp = 0 C or 300KPhase Changes- Melting: Breaking of rigid lattice; solid  liquid- Evaporation: Breaking of chemical bonds; liquid  gas- Dissociation: Breaking of molecules into atoms- Ionization: Stripping of electrons, changing atoms into plasma o Free elections and ions- Often more than one phase is presentLecture #10Matter and ShitToday1. Matter (Cont., recap)2. Inferring properties of matter from light3. Inferring motions of objects from lightReadings Chapter 5 (sections 4 and 5)Energy Levels in Atoms- Electrons in an atom are held in orbit around nucleus by electrical forceo Kind of like a planet around a sun- Can occupy many discrete orbitso Each orbit is an energy level (like the rungs on a latter  specific heights)Recap- What is the structure of mattero Matter is made of atoms, which consist of a nucleus of protons and neutrons surrounded by a cloud of electrons- What are the phases of mattero As temperature rises, a substance transforms from a solid to a liquid to a gas, then the molecules can dissociate into atoms (more than one can co-exist, thought)o Stripping of electrons from atoms (ionization) turns the substance into a plasms- How is energy stored in atoms?o The energies of electrons in atoms correspond to discrete energy levelsLearning From Light-