Contents are appropriate for IGCSE Physics

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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