Sound

Question 1

Origin of sound

Answer 1

• most sounds are waves produced by vibration of material objects
• vibrating material sends a disturbance through the surrounding medium, in the form of longitudinal waves
• in most cases, frequency of vibrating source and frequency of sound waves produced are the same

Question 2

Pitch

Answer 2

Our subjective impression about the frequency of sound

• young person can hear 20-20000 Hz
• this range gets smaller with age

Question 3

Infrasonic

Answer 3

Below 20 Hz

Question 4

Ultrasonic

Answer 4

Above 20000 Hz

Question 5

Pulse

Answer 5

No periodic sound

Question 6

Compression

Answer 6

Condensed region of medium through which a longitudinal wave travels

Question 7

Rare fraction

Answer 7

Reduced pressure of the medium through which a longitudinal wave travels
- it is not the medium that travels across the room but the energy carrying pulse

Question 8

Elasticity

Answer 8

Ability of a material that has changed shape in response to an applied force to resume its initial shape once the distorting force is removed

Question 9

Media that transmit sound

Answer 9

Relative to solids and liquids, air is a poor conductor of sound

• liquids and crystalline solids are generally excellent conductors of sound
• speed of sound is generally greater in solids than in liquids, and greater in liquids than in gases

Question 10

Speed of sound

Answer 10

• depends on wind conditions, temperature, and humidity
• it DOES NOT depend on the loudness or frequency of the sound
• sound travels through warm air faster
• for each degree rise in temperature above 0C, speed of sound increases by 0.6m/s

Question 11

Echo

Answer 11

Reflection of sound

Question 12

Transmitted wave

Answer 12

Sound energy not carried by the reflected sound wave

Question 13

Reverberations

Answer 13

Multiple refelctions

Question 14

Acoustics

Answer 14

Study of sound properties

Question 15

Refraction

Answer 15

When sound waves bend when parts of the wave fronts travel at different speeds

• sound travels slower at higher altitudes and bends away from the ground
• reflections and retractions of ultrasonic waves are used in diagnositc imaging
• when high frequency sound (ultrasound) enter the body, it is…

Question 16

Energy in sound waves

Answer 16

• only a small amount of energy is needed to produce sound
• sound energy dissipates to thermal energy while sound travels in air
• for waves of higher frequency, the sound energy is transformed into internal energy faster than for waves of lower frequency

Question 17

Forced vibration

Answer 17

Setting up of vibrations in an object by a vibrating force

Question 18

Natural frequency

Answer 18

Frequency at which an elastic object naturally tends to vibrate if it is disturbed and the disturbing force is removed
- some factors that contribute to the natural frequency of an object are elasticity and shape of object

Question 19

Resonance

Answer 19

When the frequency of forced vibrations on an object matches the object’s natural frequency and a dramatic increase in amplitude occurs
- tuning forks tuned to the same frequency and spaced about 1m apart from each other

Question 20

Constructive interference

Answer 20

Waves arrive in phase and interfere constructively when the path lengths from the speakers are the same
(Crest meets crest, trough meets trough)

Question 21

Destructive interference

Answer 21

Waves arrive out of phase and interfere destructively when the path lengths differ by half a wave length
(Crest meets trough)

Question 22

Interference

Answer 22

If a range of sounds with different frequencies are emitted, only some waves destructively interfere. There is usually enough reflection of sound to fill in cancelled spots

Question 23

Dead spots

Answer 23

Occur when sound aves reflect off walls and interfere with non-reflected waves to produce zones of low amplitude
- good anti-noise technology

Question 24

Beats

Answer 24

Periodic variation in the loudness of sound

• they are due to interference
• the sound that reached our ears throbs between max and min loudness
• when frequencies are identical, the beats disappear