A) More frequency, less wavelength
B) More frequency, more wavelength
C) Less frequency, less wavelength
D) More frequency, constant wavelength
Correct Answer: A
Solution :
Key Idea: When the distance between the source and lis-tener is decreasing, the apparent frequency increases. According to Dopplers effect, whenever there is a relative motion between a source of sound and listner, the apparent frequency of sound heard by the listner is different from the actual frequency of sound emitted by the source. Let S be source of sound and L the listener of sound. Let v be the actual frequency of sound emitted by the source and \[\lambda \] be the actual wavelength of the sound emitted. If v is velocity of sound in still air, then \[\lambda =\frac{v}{V}\] If velocity of listener is \[{{v}_{L}}\] and velocity of source is \[{{v}_{S}}\], then apparent frequency of sound waves heard by the listener is \[V=\frac{v-{{v}_{L}}}{v-{{v}_{s}}}\times v\] Here, both source and listener are approaching each other. Then \[{{v}_{S}}\] is positive and \[{{v}_{L}}\] is negative. \[\therefore \] \[V\frac{v-(-{{v}_{L}})}{v-{{v}_{S}}}v\] \[=\left( \frac{v+{{v}_{L}}}{v-{{v}_{S}}} \right)v\] ie., \[v>v\] Also, \[\lambda <\lambda \] So, listener, listens more frequency and observes less wavelength.You need to login to perform this action.
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