Intro to Physics 2nd semester topics for final exam pt. 2 Waves Mechanical waves • Fastest through solids, slowest through gases • Can only travel through matter • Ex: sound, seismic waves Non-mechanical waves • Fastest through a vacuum, slowest through solids • Can travel through matter or space • Ex: electromagnetic waves ARE THERE DIFFERENT TYPES OF WAVES? • Mechanical Waves • Non-Mechanical Waves Sound waves microwaves Electromagnetic Wave http://www.nrc-cnrc.gc.ca/obj/inmsienm/images/research_images/optical_comb/COMBFIG1.gif Waves Transverse • Vibrations occur perpendicular to wave travel • Crest, trough structure Longitudinal • Vibrations occur in same direction as wave travel • Compression-rarefaction structure TRANSVERSE WAVE crest One wavelength amplitude trough Rest position LONGITUDINAL WAVE Rarefaction (less dense) Compression (more dense) one wavelength Wave Characteristics Wave Characteristics – Frequency (f) (the number of vibrations that occur in a given time) • Hertz (Hz) (# of vibrations per second) • High frequency waves produce waves with short periods and short wavelengths – Period (P) (the time it takes for one wave cycle to pass) • Seconds (s) • The lower the frequency, the longer the period Wave Characteristics – Wavelength λ (lambda) (the distance between one point on a wave to the next identical point; crest to crest, for example) • Meters (m) • The lower the frequency, the longer the wavelength – Amplitude (longitudinal waves—the tightness of the compression; transverse waves—the distance from the crest to rest position or from trough to rest position) • Meters (m) • The greater the amplitude of the wave, the more energy the wave transfers. Sound waves Sound waves and the Ear What is the audible range of frequencies for a human? 20 -20,000 Hz What type of wave is a sound wave? Mechanical and The frequency of a sound wave is called pitch. Longitudinal Like all mechanical waves, sound waves can only travel through matter Relative intensity of sound wave is volume and is measured in decibels (dB) Seismic waves Cause • Any physical disturbance that causes the Earth to vibrate – Earthquakes (most commonly) – Volcanoes – Landslides (terrestrial or undersea) – Extraterrestrial impacts (asteroids – and meteorites) Earthquakes • Earthquakes occur when built-up stress is suddenly released. • Rupture or slippage of rock within the Earth produce seismic waves http://quake06.s tanford.edu/cen tennial/tour/sto p11.html Earthquakes 2 Earthquake Waves • Earthquake waves travel out in all directions from a point where strain energy is released. This point is the focus. • The point on Earth’s surface directly above the focus is the epicenter. 2 Body Waves— seismic waves that pass through the Earth Primary waves, also called P-waves, are longitudinal waves (compressional). • P-waves pass through solids and liquids • P-waves are faster than s-waves. Secondary waves, also called S-waves are transverse waves. • S-waves can travel through solids but not liquids • S-waves are slower than p-waves Body Fig. 9-8, p. 194 Fig. 9-10, p. 196 Three types of plate boundaries 1. Divergent plate boundary 2. Convergent Plate Boundary 3. Transform Plate boundary Fig. 1-14, p. 18 The Mechanism for Plate Motion is Convection in the Mantle Heat from the interior flows outward toward the crust Fig. 1-12, p. 15 P-waves and Swaves provide seismic evidence that the outer core is liquid and the inner core is solid Refraction: the bending of a wave as it passes from one medium to another Caused by changes in wave speed Fig. 9-21, p. 210 Benioff Seismic Zone (associated with a subduction zone at a Convergent Plate Boundary) Pattern of earthquake occurrences indicates the location of the subducted limb of the lithospheric plate Fig. 2-13, p. 37 Electromagnetic Spectrum Increasing photon energy WHAT CAUSES Electromagnetic waves (or LIGHT)? • Vibrating electrically charged particles • A changing electric field sets up a changing magnetic field, which sets up a changing electric field, and so on. Electromagnetic wave (a combination of electric and magnetic fields HOW DO WE MODEL LIGHT? • TWO MODELS – Wave Model – Particle Model • Physicists recognize the dual nature of light (light travels like a wave, but hits like a particle). • Photon: a massless particle of light (carries energy—greater the frequency, the greater the photon energy) INTENSITY OF LIGHT • An increase in the number of waves or photons (or the amount of light) • Brightness of light means intensity. • Not related to frequency or the energy per photon! Same frequencies of light, just different intensities! 100 Watts 40 Watts Photoelectric Effect: the ejection of electrons from certain metals when exposed to certain frequencies of light. Electromagnetic radiation (visible light range) Electrons emitted Photovolatic cell (solar cell) Produces electron flow (electricity) 29.2 The Law of Reflection Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal. • The angle between the incident ray and the normal is the angle of incidence. • The angle between the reflected ray and the normal is the angle of reflection. • Angle of incidence = Angle of reflection 29.4 Diffuse Reflection Diffuse reflection allows us to see most things around us. a. Light is diffusely reflected from paper in many directions. b. Light incident on a smooth mirror is only reflected in one direction. Ordinary paper has a rough surface when viewed with a microscope. 29.8 Refraction of Light As a light wave passes from air into water, its speed decreases. Refraction • The bending of light as it passes from one medium to another. • Dependent upon – Change in light wave speed – Change in direction • Bending means an abrupt change in direction. 31.1 Diffraction and Huygens’ Principle The extent to which the water waves bend depends on the size of the opening. 25.7 Interference Interference patterns occur when waves from different sources arrive at the same point—at the same time. 25.7 Interference a. In constructive interference, the waves reinforce each other to produce a wave of increased amplitude. Amplitude has doubled in height 25.7 Interference a. b. In constructive interference, the waves reinforce each other to produce a wave of increased amplitude. In destructive interference, the waves cancel each other and no wave is produced. INTERFERENCE • The combination of two or more waves that exist in the same place at the same time. • Constructive Interference (additive effect—in phase) • Destructive Interference (subtractive effect—out of phase) • http://www2.biglobe.ne.jp/%7Enorimari/science/Jav aEd/e-wave3.html • http://www2.biglobe.ne.jp/%7Enorimari/science/Jav aEd/e-wave2.html Light and colors • Primary colors of light • Red-green-blue What is color? • When we see color, we are seeing specific frequencies of visible light • VISIBLE LIGHT IS ROYGBIV • Red, orange, yellow, green, blue, indigo and violet • For visible light – Red has the lowest frequency and longest wavelength – Violet has the highest frequency and shortest wavelength Isaac Newton—discovered that white light is composed of seven different colors of light Red Orange White Light Yellow Green Blue Indigo Violet A prism disperses white light into its primary frequencies of color 28.2 Color by Reflection a. b. This square reflects all the colors illuminating it. In sunlight, it is white. When illuminated with blue light, it is blue. This square absorbs all the colors illuminating it. In sunlight it is warmer than the white square. Electricity • More electrons than protons • Negatively charged • More protons than electrons • Positively charged Voltage • Force that causes charges to move (the push or the electric field) • Voltage exists if there is a potential difference in charges (negatively charged vs. positively charged) • SI unit is Volt (V) Electric Current • The flow of charged particles. • Charges move from a position of higher to lower electric PE (or higher voltage to lower voltage). • SI unit is ampere (A or amps) Resistance • Resistance restricts the flow of electric charges. • The cause: internal friction as moving charged particles collide. • Unit for resistance is ohm Series circuit Parallel circuit http://iss.cet.edu/electricity/pages/a17.xml Match statements with the correct circuit • 1 2 3 4 5 6 Series circuit vs. Parallel circuit 1. other bulbs go out if one bulb burns out 2. bulbs maintain same brightness if more bulbs are added 3. two or more paths for electric current to flow 4. bulbs dim if more bulbs are added 5. other bulbs stay lit if one bulb goes out 6. only one path for electric current to flow