Course Information. Physics 1C Waves, optics and modern physics. Grades. Class Schedule. Clickers. Homework

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1 Course Inforation Physics 1C Waves, optics and odern physics Instructor: Melvin Oaura eail: Course Syllabus on the web page students/courses/fall2009/physics1c Instructor: Mel Oaura Office: 4517Mayer Hall Addition Office Hrs. Mon 2-3 p or by appointent TA: Chris Murphy Office: TBA Office Hrs: TBA Text. Physics 1 Serway and Faughn, 7 th edition, UCSD custo edition. Volue 1 and Volue 2 Class Schedule Lectures Tu, Thu. 11:00-12:20 p Yor Hall 2722 Quizzes Third Tue. 11:00-12:200 p Yor Hall 2722 Proble Session TBA Grades Quizzes (3) will be held on Tue as scheduled. You are allowed to drop 1 quizzes. There will be no ae-up quizzes. Final exa covering the whole course. The final grade will be based on Quizzes 60% (best 2 out of 3 quizzes) Final exa 40% Extra credit 5% (clicer responses) Hoewor Hoewor will be assigned each wee. Hoewor will not be graded but quiz questions will reseble the hoewor. Solutions to the hoewor probles will be posted on the web page. Clicers Interwrite Personal Response Syste (PRS) Available at the boostore Clicer questions will be ased during class. Student responses will be recorded. 2 points for each correct answer 1 point for each incorrect answer. The clicer points (up to 5% ) will be added to your score at the end of the quarter

2 Laboratory The laboratory is a separate class which will be taught by Professor Anderson. Waves and Modern Physics Oscillations and Waves Sound, light, radio waves, icrowaves Optics Lenses, irrors, caeras, telescopes. Interference, diffraction, polarization Quantu Mechanics Quantu echanics, atos, olecules, transistors, lasers Nuclear Physics Radioactivity, nuclear energy 1.1 Siple Haronic Motion Kineatics Sinusoidal otion Dynaics -Newton s law and Hooe s law. Energetics Conservation of Energy Exaples Mass on a spring Pendulu Properties of SHM Tie for oscillations is independent of the aplitude of the oscillation. Useful as a tiing device. SHM is exhibited by echanical systes which follow Hooe s Law Hooe s Law F= x F - Force - Force constant Units (N/) x displaceent fro equilibriu position Hooe s Law F = - x Force (F) slope =- 0 Displaceent (x) 0 Hooe s law alost always holds for sall displaceents Equilibriu position

3 The force of gravity is cancelled by the force of the spring. Vertical direction Equilibriu position The force on the object is proportional to the displaceent fro the equilibriu position. F = y Hooe s Law is obeyed. y F y y Displaceent Description of Siple Haronic Motion T Tie x=acosωt Aplitude - A (axiu displaceent, ) Period - T ( repeat tie, s) Frequency - f = 1 Cycles/s (Hertz) T Angular Frequency ω = 2πf = (radians /s) sinusoidal function displaceent, velocity, acceleration X x = A cos( ωt) Tie dx v = = ωasin( ωt) dt The projection of the rotating vector A on the x axis generates a sinusoidal function useful in visualizing sinusoidal otion. 2π x = A cos( θ ) = A cos( t) = A cos(2π ft) = A cos( ωt) T dv = = ω ω dt 2 a Acos( t) t x, v and a are sinusoidal functions with different initial phase angles. The agnitudes of v and a are ultiplied by ω or ω 2 to preserve the units. Exaple A ass on a spring is oscillating with a period of 0.5 s and aplitude of 2.0 c. The top trace shows the displaceent vs tie for a haronic oscillator. Does the botto trace show the value of v or a? What is the frequency? What is the angular frequency? What is the axiu speed? What is the axiu acceleration? What is the position of the ass when the speed is axiu? What is the position of the ass when the acceleration is axiu? 2.0 X (c) -2.0 V or a? t ( s)

4 The frequency is deterined by Newton s Law a gives ω= F = a s F = x = Acosωt s 2 a = ω Acosωt 1 f = 2 π } T = 2π For sinusoidal otion. Frequency of the ass on a spring T = 2π F=-y How does the period depend on ass? How does the period depend on the force constant? How does the period depend on the aplitude? Deo Find the force constant of a spring and calculate the oscillation frequency. Proble A 75 g student steps into a car with a ass of 1500 g and the car is displaced downward by 1.0 c. As she drives off she goes over a bup and the car (which has poor shoc absorbers) oscillates. What is the frequency of oscillation. Springs in parallel Suppose you had two identical springs each with force constant fro which an object of ass was suspended. The oscillation period for one spring is T o. What would the oscillation period be if the two springs were connected in parallel? A. 2T o B. T o /2 C. 2 1/2 T o D. T o /2 1/2 Springs in series Suppose you had two identical springs each with force constant fro which an object of ass was suspended. The oscillation period for one spring is T o. What would the oscillation period be if the two springs were connected in series? A. 2T o B. T o /2 C. 2 1/2 T o D. T o /2 1/2

5 Energy Energy required to stretch (copress) a spring by a displaceent x F 1 2 E = x 2 Oscillation between KE and PE Total energy =KE+PE = constant PE ax KE ax KE ax F x Wor = F average x F average =½ x PE ax Note the energy depends on x 2 so it is independent of the sign of x, i.e. sae for copression and stretch. Pendulu The restoring force is proportional to the displaceent for sall displaceents. F = gsinθ F = gθ for sall θ g F= s L Equivalent to Hooe s Law with =g/l ω= ω= g L then becoes T = 2π L g The period is dependent on L but independent of Question How can you deterine the value of g using a pendulu? Question How does the period of a pendulu depend on L? How does the period depend on M? How does the period depend on aplitude? Question Suppose you drop a ball to the floor and it rebounds after a perfectly elastic collision with the floor and continues to bounce. Does the ball display siple haronic otion? Would this syste be useful as a cloc device?

6 Applications of haronic oscillators Clocs are iportant for navigation Pendulu clocs -10s/day Crystal oscillators- Quartz watches - 0.1s/day Atoic clocs Tie standards based on atoic transition frequencies s/day Longitude: The True Story Of The Lone Genius Who Solved The Greatest Scientific Proble Of His Tie Global positioning satellites deterine positioning using accurate clocs John Harrison Forced vibrations and resonance The periodic force puts energy into the syste Resonance When the driving oscillations has a frequency that atches the oscillation frequency of the standing waves in the syste then a large aount of energy can be put into the syste. The push frequency ust be at the sae frequency as the frequency of the swing. The driving force is in resonance with the natural frequency. Coupled Oscillations When two oscillators are coupled by an interaction, energy can be transferred fro one oscillator to another. The rate of energy transfer is faster when the two oscillators are in resonance. Fast transfer Slow transfer