[填空题]
An ultrasound source;*g k4lwgyyj /rcc/p. passes 7l2hi-j -1b 9fdv hveoby a stationary sound detector with a constant speed -i1hdoe-2vb 7l9v hfjof $v$. The angle between the direction of the motion of the source and the line to the detector from the source is $30^{\circ}C$.
1.Describe the Doppler effect.
2.The frequency of the wave emitted by the source is 21 000 Hz. The average speed of ultrasound in the air is $350\,ms^{−1}$
For the orientation shown in the diagram, the detector receives an ultrasound that has a 27 Hz difference in the frequency from 21 000 Hz. Calculate the speed of the source. $u_s$ = $ms^{-1}$
3.The angle between the direction of the motion of the source and the detector is increased up to $90^{\circ}C$ at a steady rate. Sketch a graph that shows how the observed frequency $′f′$ by the detector varies with time $t$. (no need to add values on the axis)
$f_0$′ is the initial detected frequency and $f$ is the frequency of the wave emitted from the source.
2.(1)Another application of the doppler effect is calculating the speed of satellites.
A geostationary satellite is a satellite that is used for broadcasting. Its position is fixed above a stationary television receiver on earth. It undergoes circular motion with a speed of $8.0\,kms^{−1}$ and the emitted frequency for a channel is $3.0\times10^5\,Hz$. What is the frequency that should be set on the television on earth to be tuned with the channel? $10^5\,Hz$
2.While changing the position of a satellite, it approaches the earth at a constant speed. Explain, adding wavefronts to the diagram, any difference between emitted frequency from satellite and received frequency by the television.
