Name: ______________________________________________________ Date: ___________________________ Physics Unit 6 Review ANSWER KEY Directions: On a separate sheet of paper, answer the following questions based upon your notes for Unit 6. For the math problems, be sure to show all of your work including an answer with correct units. Simple Harmonic Motion What is simple harmonic motion? Any periodic motion that is the result of a restoring force. What is period? The time it takes for an object to complete one full cycle of motion. What is frequency? The number of complete cycles an object goes through per unit of time. What is the relationship between period and frequency? T= 1/f What is the restoring force? Hooke’s Law: Fs= -kx When is acceleration at a maximum? Acceleration is a maximum when displacement is a maximum. When is velocity at a maximum? Velocity is a maximum when displacement is at equilibrium or displacement is 0. When is the restoring force at a maximum? Restoring force is a maximum at maximum displacement. What is the formula for calculating the period of a spring that oscillates in simple harmonic motion? (Write down what each variable stands for) T= 2pi * sqrt(m/k) The Simple Pendulum What is the restoring force equal to on a Pendulum? The weight of the bob. What are the only two forces acting in a pendulum system? Weight of the bob and tension in the string. When is the gravitational potential energy at a maximum? Why? When displacement from equilibrium is at a maximum because the bob is at it’s maximum height. GPE = mgh What is the formula for calculating the period of a simple pendulum? (Write down what each variable stands for) T= 2pi * sqrt(l/g) Properties of Waves Draw a graph of a sinusoidal wave (yes, the same wave we have been drawing this whole time) and label the following things: o Amplitude (maximum displacement from equilibrium), wavelength (distance between two points on a wave that behave the same) , trough (lowest point on a wave), crest (highest point on a wave) How do you measure the wavelength on a graph? Crest to crest OR trough to trough What is the fundamental wave equation? (Write down what each variable stands for) v=fλ f=frequency, v=velocity, λ= wavelength What are the two types of waves? Transverse & Longitudinal How does the motion of the wave compare to the vibrations of the wave in each of the types of waves? Transverse – wave motion and wave vibrations are perpendicular to one another, Longitudinal – wave motion and wave vibrations are parallel to one another. Interference What is the superposition principle? If two or more traveling waves are moving through a medium, the resulting wave is found by adding together the displacements of the individual waves point by point Define constructive interference and how to find it if given a graph. (Hint: what two points on a wave must meet) When two waves meet at the same point (crest to crest, trough to trough) in order to add their amplitudes together to create a bigger wave. Define destructive interference and how to find it if given a graph. (Hint: what two points on a wave must meet) When two waves meet at different points (crest to trough) in order to subtract their amplitudes to create a smaller wave. Name: ______________________________________________________ Date: ___________________________ What happens to the wave pulses AFTER they interfere with one another? Waves move as if they never interfered, completely unchanged. Sound What type of wave is a sound wave? Longitudinal What is the speed of sound in air? 343 m/s What are the two areas you can identify on a sound wave? Compression & Rarefaction, compression corresponds to crests, rarefaction corresponds to troughs How are pitch and frequency related? Pitch is the brain response, what you hear when a certain frequency is emitted from a sound source. How can a tuning fork be used to show a sound wave? Tuning fork when vibrating creates areas of high and low densities which creates areas of rarefaction and compression thereby creating a soundwave. What are the three different categories of sound waves? Describe each in comparison to what we can hear and give an example of each. Ultrasonic – above what we hear Ex: Dog Whistles, Audible – what we hear between 20 Hz to 20,000 Hz, Infrasonic – below what we hear Ex: Earthquakes What is the Doppler effect? (Think of Sheldon’s Halloween Costume) Wave phenomena that occurs whenever there is relative motion between an observer and a sound source and a perceived frequency is heard due to this relative motion. o When sources move toward each other what happens to the perceived sound? Perceived sound/pitch/frequency is higher o When sources moves away from each other what happens to the perceived sound? Perceived sound/pitch/frequency is lower. What is resonance? Give an example When an object begins to oscillate at its natural frequency due to a driving force. Describe what happened in the Tacoma Narrows Bridge collapse. Bridge was forced to oscillate at its natural frequency due to the driving force of wind and eventually the bridge could not withstand the motion any longer and collapsed. Light What are the two forms that light takes on? Light either acts as a wave or a particle (photon). What are electromagnetic waves? Light waves that we may not necessarily can see but they still exist and can be located on the electromagnetic spectrum. Is visible light included on the electromagnetic spectrum? Yes, in all the colors. What is the electromagnetic spectrum? Spectrum that shows all of the possible forms of electromagnetic waves including their wavelengths in relation to one another. Are there specific ranges for each type of electromagnetic waves? (Hint: Do sections overlap or not) No, they overlap with one another and the ranges are essentially continuous. What is the speed of light? 3.0 x 108 m/s How does the distance you are from light source affect brightness? The further away you are from a light source, the less bright it appears because the light spreads out into the air as you move further away. When light is reflected off of a surface, how does the angle of incidence compare to the angle of reflection? They are equal. Angle of incidence = Angle of reflection What is refraction? When part of a light wave enters into a medium and bends based upon the properties and conditions of that medium. When a ray of light goes from a medium of HIGH index of refraction to a medium of LOW index of refraction… o What happens to the speed of the light ray? Increases o How does the light bend with regards to the normal? Away When a ray of light goes from a medium of LOW index of refraction to a medium of HIGH index of refraction… o What happens to the speed of the light ray? Decreases Name: ______________________________________________________ Date: ___________________________ o How does the light bend with regards to the normal? Toward What is the formula for finding the velocity of light in a specific medium using the index of refraction for that medium? n = c/v What is Snell’s law? n1sintheta1 = n2sintheta2 What is total internal reflection? What has to happen in order for it to occur? A light ray is reflected within a medium when a light ray tries to leave a medium with a high index of refraction to a medium with a low index of refraction. What is the critical angle? When does it happen? How can you calculate it? Critical angle is the angle needed to have a refracted angle of 90 degrees. Can only occur when n1 > n2. Practice Problems 1. What is the period of a spring with a spring constant of 50 N/m with a 20 kg mass hanging from it? 3.97 seconds 2. What is the frequency of a wave that oscillates at a period of 50 seconds? .02 Hz 3. What is the period of a 11.11 m long pendulum? 6.68 seconds 4. What is the speed of a wave that has a 600 m wavelength and a period of 60 seconds? 10 m/s 5. What is the speed of light in a block of glycerol? 2.04 x 108 m/s 6. What is the speed of light in a cup of corn oil? 2.04 x 108 m/s 7. What is the critical angle of a ray of light that goes from diamond to water? 33.34o 8. What is the critical angle of a ray of light that goes from air to water? Can only occur if n1 > n2 9. What is the angle of refraction of a ray of light that goes from air to alcohol and has an angle of incidence of 35o? 25.74o 10. What is the index of refraction of a mystery substance if a ray of light goes from air at an angle of incidence of 75o and refracts at an angle of 52o? 1.23

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# Physics Unit 6 Review ANSWER KEY