Waves: Miscellaneous Doppler Effect Standing Waves
Doppler Effect • Observed whenever the source of waves is moving with respect to an observer. • An apparent upward shift in frequency for the observer when the source is approaching • An apparent downward shift in frequency for the observer when the source is receding. • NO effect for the source - or an observer moving with the source
Doppler Effect • Effect does not result because of an actual change in the frequency of the source. • Can be observed for any type of wave - water wave, sound wave, light wave, etc. • Most familiar with the Doppler effect because of our experiences with sound waves-> sirens! • Animation
Concept Question A music fan at a swimming pool is listening to a radio on a diving platform. The radio is playing a constant frequency tone when this fellow, clutching his radio, jumps off. Describe the Doppler effect heard by: a) a person left behind on the platform b) a person down below floating on a rubber raft. In each case, specify whetherthe observed frequency is constant or – if it changes - how does theobserved frequency change while the music fan is falling.
Concept Question • Suppose you are standing on the passenger-loading platform of the commuter railway line. As the commuter train approaches the station, it gradually slows down. During this process of slowing down, the engineer sounds the horn at a constant frequency of 300 Hz. What pitch or changes in pitch will you perceive as the train approaches you on the loading platform?
Other Applications • Bats • Doppler Radar: Weather, Speeding Cars • Medical Imaging • Astronomy: Expansion of the Universe • Sonic Boom: Sound Compression
Standing Waves • Pattern which results from the interference of two or more waves along the same medium. • Standing wave patterns are always characterized by an alternating pattern of nodes and antinodes. • Phet Animation
Standing Waves • Nodes: point of no displacement. • Occur where two waves exhibit destructive interference • Anti-nodes: point of maximal displacement. • Occur where the two interfering waves are always undergoing constructive interference. • Standing Wave Animation
Concept Question Consider the standing wave pattern shown below. A wave generated at the left end of the medium undergoes reflection at the fixed end on the right side of the medium. The number of nodes? The number of antinodes? How many waves?
Concept Question • A node is a point located along the medium where there is always ______.A - a double crestB - a double troughC - constructive interferenceD - destructive interferenceE - a double rarefaction