Lesson 4 — Decibel scale

• Science
• Middelbare school
• havo, vwo
• Leerjaar 2

Chapter 5

Understanding waves

 (§5.4 + §5.5)

This lesson

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

The decibel

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

Decibel meter

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

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

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

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

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

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

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?

Sound is a wave

What is a wave?

• A disturbance that gets passed on through a medium
  

A wave

A wave

How many waves do we see here?

A wave

How many waves do we see here?

1 Wave

A wave

How many waves do we see here?

The properties of a wave

• Frequency
  
• Amplitude

•  Wavelength
• Wave speed

Tone generator

Oscilloscope

A wave

How many waves do we see here?

The properties of a wave

Tone generator

Oscilloscope

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)

 Wave Quiz

Q1) What is the wavelength of this wave?

One block is 2 cm long

Q2) What is the amplitude of this wave?

One block is 2 cm long

Q3) What is the frequency of this wave?

1 second

 Q1) What is the wavelength of this wave?

One block is 2 cm long

8 cm

Q2) What is the amplitude of this wave?

One block is 2 cm long

4,5 cm

Homework

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