Question

The motion detector used in a physics lab sends and receives 30 kHz ultrasonic pulses. A pulse goes out, reflects off the object being measured, and returns to the detector. The lab temperature is 20 ∘C.

Answer 1

Answer

Given,

Frequency of the ultrasonic pulse = 30 kHz

Speed of the sound = v = 343 m/s

wavelength of the wave emitted = ?

using formula

     $v = \nu \lambda$                    

     $\lambda= \dfrac{v}{\nu}$                  

     $\lambda= \dfrac{343}{30\times 10^3}$

     $\lambda=11.43 \times 10^{-3}\ m$          

     $\lambda=11.43\ mm$                    

time taken for a pulse  that reflects off an object 3.0 m away to make a round trip                                                

   $time = \dfrac{\Delta x}{\Delta v}$

   $time = \dfrac{2\times 3}{343}$

            t = 0.01749 s

            t = 17.49 ms