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Activity B1-WA due by 4 pm Friday 03/28 Chapter 5 Mallard HW quiz – Due by 12 AM Thursday 03/27 Chapter 5 quiz in class on Thursday 03/27 Tuesday, March 25 Spring 2008 Electricity and Magnetism Chapter 5 Great Idea: Electricity and magnetism are two different aspects of one force—the electromagnetic force Batteries and Electrical Current • Electrical current – Flow of charged particles – Symbol: I – Units: Coulombs/second (C/s) • Voltage – the difference in electrical charge between two points in a circuit (electrical “pressure”) – Symbol: V – Units: volts (V) • Battery – Converts chemical energy to kinetic energy (energy of flowing charges) Electric Circuits • Electric circuit – Unbroken path of material carrying electricity • Circuit components 1. Source 2. Closed path 3. Device to use electrical energy • Ohm’s Law – Current is directly proportional to voltage V and inversely proportional to resistance R – In symbols: I = V / R • Electric Power: P = I × V Magnetic Effects from Electricity • Oersted – Magnetic field created by motion of electrical charges • Magnetic Monopole – Does not exist – Magnetism is related to arrangement of electrical charges in atoms • Electromagnet Electric Motors & Magnetism Electrical Effects from Magnetism • Faraday – Electromagnetic induction – Electrical fields and currents can be produced by changing magnetic fields • Electric Generator Maxwell’s Equations • Coulomb’s Law • No magnetic monopoles • Magnetic phenomena produced by electrical effects • Electrical phenomena produced by magnetic effects Chapter 6 Waves & Electromagnetic Radiation Great Idea: Whenever an electrically charged object is accelerated, it produces electromagnetic radiation—waves of energy that travel at the speed of light Waves A wave is a traveling disturbance that transports energy from one place to another without transporting matter across the intervening distance. Simple Oscillations • Oscillation – back-and-forth motion about an equilibrium position • Cycle – one complete oscillation or repetition of a periodic motion • Period, T – the length of time required for one cycle • Frequency, f – number of cycles that occur during a unit of time f=1/T • Amplitude – distance traveled above or below equilibrium position Properties of Periodic Waves A periodic wave is a wave made of a series of pulses separated by equal time intervals. l f v time between wave crests Speed of wave: v=f l Sample Exercise Suppose that water waves have a wavelength of 1.4 m and a period of 0.8 s. What is the frequency of these waves? What is the velocity of these waves? Sample Exercise A wave on a rope is shown in the diagram. a. What is the wavelength of this wave? b. If the speed of the wave is 6 m/s, what is its frequency? Two Basic Wave Types Longitudinal wave – motion in same direction as wave Transverse wave – motion perpendicular to wave direction Sound Waves A sound wave is a periodic longitudinal wave of pressure variations propagating through a medium. http://electronics.howstuffworks.com/speaker5.htm Sound Waves The shapes of instruments and the materials they’re made of influence the pitch and timbre of the sound they create... Pitch of sound is determined by its frequency and speed High frequency = high pitch; low frequency = low pitch Sound Waves L=½l Sound waves travel at about 340 m/s (≈ 760 mi/h) in air Doppler Effect Apparent shift in frequency of a wave emitted from or received by a moving source Wave Interference – Constructive Interference • Add together – Destructive Interference • Cancellation wave addition Electromagnetic Waves Self-propagating radiant energy Energy transferred by oscillating electric and magnetic fields created by accelerated charges Electromagnetic waves continue through internal mechanisms and transfer energy as they travel; they do not require a medium to travel. Speed of Light All electromagnetic waves travel at the same speed v=f l=c c = 3 × 108 m/s = 186,000 Energy of wave: E = hf mi/s (h is Planck’s constant = 6.626 × 10-34 m2·kg/s) Higher frequency visible light = blue color Lower frequency visible light = red color Interaction of EM Waves & Matter Transmission: wave passes through matter refraction & dispersion Absorption: wave & energy are absorbed Scattering: wave & energy absorbed and reemitted diffuse scattering reflection The Blue Sky – Light Scattering Molecules in the air preferentially scatter high frequency blue light waves – sky appears blue when viewed away from direct sunlight http://math.ucr.edu/home/baez/physics/General/ BlueSky/blue_sky.html Sky appears white around the Sun – yellow/orange/red when light traverses long distances through the atmosphere Electromagnetic Waves & the Doppler Effect Apparent shift in frequency of a wave emitted from or received by a moving source Higher frequency light: “blueshifted” Lower frequency light: “redshifted”