Lesson 6 — 2B

• Science
• Middelbare school
• vwo
• Leerjaar 2

5.7 Echoes

This lesson

•  Recap
• Echoes
• Practice exercises
• Time to study

Learning goals

• Be able to calculate wave speed.
• Explain in your own words how echoes work.
• Describe how echo location works.
• Be able to do calculations involving echoes and echo location

Recap

The distinct sound of 

musical instruments

Main frequency 

(the fundamental) 

with other frequencies mixed in (harmonics)

The distinctive sound that an instrument makes is called its timbre

The mach system

How does it work?

What is mach 1

What is mach 2

What is mach 3?

Mach 1, Mach 2, Mach 3

• Mach 1: traveling at 343 meters per seconds
  
• Mach 2: traveling at 686 meters per seconds
  
• Mach 3: 1029 meters per seconds
  
• The fastest skydiverer, Felix Baumgartner, traveled at mach 1.1, how fast did he fall?
  

5.6 Making simple calculations

• v: speed (m/s)
  
• f: frequency (Hz)
  
• λ: Wavelength (m)
  

v=f⋅λ

f=​T​​1​​

• f: frequency (Hz)
  
• T: Period (s)

Practice exercise

a) A wave has a wavelength of 0.5 meters and a frequency of 120 Hz. What is the wave’s speed? 

b) A soundwave is traveling through a steel katana. The wavelength of this wave is 3,725 m. The speed of sound in steel is 5960 m/s. Calculate the period of this wave.

5.7 Echoes

Echo location

Calculation exercise

A man has set out the find the deepest well in the world. Once he found it he clapped his hands above it. He timed how long it took before he heard an echo. It took 71.4 seconds. The speed of sound in air is 330 m/s. 

Calculate how deep the well is.

Calculation exercise

Dolphins can make sounds with a frequency as low as 0.2 Hz and as high as up to 150.000 Hz. A dolphin makes use of echo location. He sends out a signal, with fish floating 240 meters away.  It takes 0.32 seconds before he hear the echo. The wavelength of the sound wave he produced is 0.01875 m. Calculate the frequency of this sound wave.

Learning goals

• Be able to calculate wave speed.
• Explain in your own words how echoes work.
• Describe how echo location works.
• Be able to do calculations involving echoes and echo location