Lesson 4 — Decibel scale

Chapter 5
Understanding waves
 (§5.4 + §5.5)
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Chapter 5
Understanding waves
 (§5.4 + §5.5)

Slide 1 - Diapositive

This lesson
  •  The decibel scale
  • What is a wave?
  • The properties of a wave
  • Wave quiz

Slide 2 - Diapositive

The decibel
  • the unit of sound intensity
  • Symbol — dB.
  • Invented in 1920 by New York telephone engineers.

Slide 3 - Diapositive

Can you find the pattern?
  • Office noise — Heavy traffic: 10 times louders
  • Office noise — Subway, shouted conversation: 100 times louder
  • Office noise —  School dance: ... times louder

Slide 4 - Diapositive

Can you find the pattern?
  • Office noise — Heavy traffic: 10 times louders
  • Office noise — Subway, shouted conversation: 100 times louder
  • Office noise —  School dance: 1000 times louder

Slide 5 - Diapositive

How the decibel scale works
  • For every step of 10 decibel up the sound gets 10 times louder.
  • From 70 to 80 dB, the sound gets .... times louder
  • From 70 to 90 dB, the sound gets .... times louder
  • From 70 to 100 dB, the sound gets .... times louder

Slide 6 - Diapositive

How the decibel scale works
  • For every step of 10 decibel up the sound gets 10 times louder.
  • From 70 to 80 dB, the sound gets 10 times louder
  • From 70 to 90 dB, the sound gets .... times louder
  • From 70 to 100 dB, the sound gets .... times louder

Slide 7 - Diapositive

How the decibel scale works
  • For every step of 10 decibel up the sound gets 10 times louder.
  • From 70 to 80 dB, the sound gets 10 times louder
  • From 70 to 90 dB, the sound gets 100 times louder
  • From 70 to 100 dB, the sound gets .... times louder

Slide 8 - Diapositive

How the decibel scale works
  • For every step of 10 decibel up the sound gets 10 times louder.
  • From 70 to 80 dB, the sound gets 10 times louder
  • From 70 to 90 dB, the sound gets 100 times louder
  • From 70 to 100 dB, the sound gets 1000 times louder

Slide 9 - Diapositive

Question
a) Two people are investigating sound intensity levels in decibel. One of them measures background music to have a sound intensity of 60 dB.  The other one measures a busy subway station to have a sound intensity of 90 dB. How much louder is a busy subway compared to background music?

Later they measure leaves rustling to have a sound intensity of 30 dB. Another sound source they measure makes sound that is 100 times louder. A third sound source they measure makes a sound that is 10.000 times louder. 
b) what was the second sound source they measured?
c) What was the third sound source they measured?

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Sound is a wave

Slide 11 - Diapositive

What is a wave?
  • A disturbance that gets passed on through a medium

Slide 12 - Diapositive

Slide 13 - Vidéo

A wave

Slide 14 - Diapositive

A wave
How many waves do we see here?

Slide 15 - Diapositive

A wave
How many waves do we see here?
1 Wave

Slide 16 - Diapositive

A wave
How many waves do we see here?

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The properties of a wave
  • Frequency
  • Amplitude
  •  Wavelength
  • Wave speed

Slide 18 - Diapositive

A wave
How many waves do we see here?

Slide 19 - Diapositive

The properties of a wave
Frequency
  •  The amount of waves per second — Unit: Hertz (Hz) — influences the tone of a sound

Amplitude
  •  The distance from the centre of the wave to the top or the bottom in meters (m) — influences the loudness of a sound

Wavelength
  •  The length of one wave in meters (m)

Wave speed
  •  The speed of the wave in meters per second (m/s)

Slide 20 - Diapositive

 Wave Quiz

Slide 21 - Diapositive

Q1) What is the wavelength of this wave?
One block is 2 cm long

Slide 22 - Diapositive

Q2) What is the amplitude of this wave?
One block is 2 cm long

Slide 23 - Diapositive

Q3) What is the frequency of this wave?
1 second

Slide 24 - Diapositive

 Q1) What is the wavelength of this wave?
One block is 2 cm long
8 cm

Slide 25 - Diapositive

Q2) What is the amplitude of this wave?
One block is 2 cm long
4,5 cm

Slide 26 - Diapositive

Homework
  • Watch the following video.
  • Make a summary of it. 
  • Be able to show your summary next lesson.

Slide 27 - Diapositive

Slide 28 - Vidéo