This document discusses the reflection and refraction of sound. It explains that hard surfaces reflect sound waves, creating an echo. The time it takes for an echo to return is used to calculate the distance to the reflecting surface. Sound travels at different speeds in various materials. Refraction occurs when sound waves travel from one medium to another, such as underwater. The document also covers pitch, frequency, amplitude, and loudness of sound waves. It describes how ultrasound, which is above the human hearing range, has various uses such as metal testing and medical scanning.

1. Refraction and reflection of sound
Sound

2. 1. Reflection of sound
 Hard surfaces reflect sound.
 Reflected sound is called Echo.
-Sound travels from the mouth to the wall and back to the ear.
-Sound travels twice the distance between the man and the wall.
-The time taken for sound to move from the man to the wall and back to the man
is called echo time.

3. d
- Distance travelled by sound = 2d
- Time taken for sound to travel to the wall and back = echo time
Therefore;
speed of sound = distance travelled = 2 x distance to wall
time taken echo time

4. Speed of sound in different materials
Medium sound speed (m/s)
air (0C) 330
water 1400
gold 3240
brick 3650
wood 4000
concrete 5000
glass 5100
steel 5790
aluminum 6420

5. Example:
1. A ship is 220m from a large cliff when it sounds its foghorn. The speed of sound
in air = 330m/s
a. when the echo is heard on the ship, how far has the sound travelled?
2 x d = 2 x 220
= 440m
b. what time delay is there before the echo is heard?
echo time = 2 x d = 2 x 220 = 440
speed 330 330 = 1.33 sec
c. the ship changes its distance from the cliff. When the echo time is 0.5sec how
far is the ship from the cliff?
2 x d = speed x echo time
2 x d = 330 x 0.5
2 x d = 165m
Therefore d = 165
2 d = 82.5m

6. Exercise
1. When the horn of the ship is
sounded, the passengers hear
an echo from a cliff after 4.0 s.
How far away is the cliff?
2. A boy is stranded on an island. He shouts for help
but all he can hear in reply is the echo of his shout
from the cliff 500 m away. What is the time
interval between the boy shouting and hearing the
echo?

7. Echo sounding
 The process of using echoes of different sounds to
measure distance and time is called echo sounding.
 The principle of echo sounding is used in the
following processes:
 Echo-sounder: used by boats to measure the depth of water.
 Electronic-tape measure: used by surveyors to measure distance
between walls.
 Radar: microwaves are used to detect the positions of aircrafts
using the principle of echo-sounding.
 Used by animals to measure distances.

9. 2. Refraction of sound
Sound waves can:
 undergo refraction.
 travel from one medium to another. E.g.
 A person under water can hear sounds made above the
water.
 Can bend or change direction
 A person behind a hill can hear a gun shot from the
other side of the hill.

10. Quality of sound
1. Frequency and Pitch
- The sharpness of sound is called pitch.
- Pitch is related to frequency.
- The higher the frequency, the higher the pitch.
- The human ear can hear sounds of frequencies between
20Hz and 20kHz (20 000Hz)
PITCH FREQUENCY
High Upper limit of hearing 20 000Hz
Whistle 10 000Hz
High note (soprano) 1 000Hz
Low note (bass) 100Hz
Low Drum note 20Hz

11. exercise
Using the wave equation, calculate the wavelengths
and complete the table below. Speed of sound in air =
330m/s
PITCH FREQUENCY WAVELENGTH
High Upper limit of hearing 20 000Hz
Whistle 10 000Hz
High note (soprano) 1 000Hz
Low note (bass) 100Hz
Low Drum note 20Hz

12. 2. Amplitude and loudness.
- Loudness is how high or low the sound is to the ear.
- Loudness is related to amplitude.
- The higher the amplitude, the louder the sound.

13. A B
C D
Which sound or sounds has/have
(a) the same pitch as A?
(b) the same loudness as A?
(c) the same pitch as B?

14. Ultra sound
 Sounds of frequencies higher than the highest
hearing limit of human beings (higher than
20kHz) is called ultra sound.
 Sounds below 20Hz are called Infrasound.

15. Uses of Ultra-sound
 Metal testing: Ultrasound is used to detect leakages in metal
pipes.
 Scanning the womb:
 Cleaning and breaking: ultrasound is used for cleaning
surfaces of delicate machinery. It is also used in the making of
fine glass instruments such as pipettes and burettes.
 some animals e.g. bats and dolphins, use ultrasound in echo
sounding to navigate.

17. Thanks
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