The motion detector used in a physics lab sends and receives 45 kHz ultrasonic p
ID: 1521121 • Letter: T
Question
The motion detector used in a physics lab sends and receives 45 kHz ultrasonic pulses. A pulse goes out, reflects off the object being measured, and returns to the detector. The lab temperature is 20 C. You may want to review ( page ) . For help with math skills, you may want to review: Substituting Numbers into Mathematical Expressions Part A What is the wavelength of the waves emitted by the motion detector? Express your answer using two significant figures. PART B How long does it take for a pulse that reflects off an object 3.0 m away to make a round trip?
Explanation / Answer
a)n=45000Hz
as temperature is 20 degree velocity of sound=330+20*0.6=342m/sec
as velocity of sound increases by 0.6m/sec for every 1 degree raiseof temperature.
v=n
wavelength==v/n=342000mm/45000=7.6mm
b)time =distance /velocity
as it is round trip time=2*distance/velocity=2*3/342
=0.0175m
=17.5 msec