1. Unit 6 Chapter 18 & 19 Sound and Light
P. Sci.
Unit 6
Chapter 18 & 19
Sound and Light

2. Sound Sound travels as longitudinal waves
All sound is produced by vibrating objects.
Sounds must have a medium to travel through (mechanical wave)

3. Properties of Sound
The speed of sound waves depends on the medium it travels through.
Two properties that affect the speed are temperature and density.

4. Loudness (intensity) Depends on your distance from the source.
on the energy of the wave
the greater the amplitude – the more energy carried – the louder the sound.

5. It is measured in decibels (dB) 0 dB – 120 dB
Relative intensity is found by comparing a sound with the quietest sound a person can hear.
It is measured in decibels (dB)
0 dB – dB
quietest sound – threshold of pain

6. Pitch How high or low a sound is.
It is determined by the frequency of the sound wave.
High frequency =high pitch sound Low frequency = low pitch sound

7. Human Hearing The human ear can hear sounds from 20 Hz to 20,000 Hz.
Infrasound – any sound with a frequency below human hearing.
Ultrasound – any sound with a frequency above human hearing.

8. How we Hear
The ear converts vibrations in the air (compressional waves) into nerve impulses that travel to the brain.

9. Sonar
Sonar systems determine distance by measuring the time it takes for sound waves to be reflected back from a surface.
d = v x t
d = distance t = time of reflection
v = average speed of sound waves in water

10. Ultrasound reflection
Ultrasound waves (between 1 – 15 million Hz) are used to produce sonograms (computerized images)
Used to view organs inside the body without having to perform surgery.

11. Review What does the speed of a sound wave depend on?
What is Pitch determined by?
How is relative intensity found?
How do we use sound reflection?