Answer to Question #164375 in Optics for Ulrich

Question

 (a.) Explain the term Doppler effect.

  A car sounding an alarm of frequency 512Hz is approaching a stationary car at a speed of 10ms^-1

 (b.) Explain why the driver of the stationary car has the impression that the frequency of the sound is

    increasing.

Answer 1

(a) Doppler Effect refers to the change in wave frequency during the relative motion between a wave source and its observer.

$f_I=\dfrac{340}{340-10}\times 512=526.34\ Hz$

$\\ f_P=\dfrac{340+10}{340}\times 526.34=537.68\ Hz$

(b) Sound is a longitudinal pressure wave. As the alarms distance became less , the air molecules get compressed together. The wavelength of the sound (these pressure waves) decreases, and the frequency increases. That results in a higher sound pitch