Quick Review Flashcards - Click to flip and test your knowledge!
Question
What defines the 'audible range' of frequency for a healthy human ear?
Answer
$20\text{ Hz}$ to $20,000\text{ Hz}$
Question
Sound waves with a frequency above $20,000\text{ Hz}$ are classified as _____.
Answer
ultrasonic
Question
What term is used for sound frequencies below $20\text{ Hz}$?
Answer
infrasonic
Question
Term: Amplitude ($a$)
Answer
Definition: The maximum displacement of a particle of the medium on either side of its mean position.
Question
Define 'time period' ($T$) in the context of wave motion.
Answer
The time taken by a particle of the medium to complete one full vibration.
Question
What is the 'frequency' ($f$) of a wave?
Answer
The number of vibrations made by a particle of the medium in one second.
Question
The distance travelled by a wave in one time period of vibration is called the _____.
Answer
wavelength ($\lambda$)
Question
Formula: Wave velocity ($V$)
Answer
$V = f\lambda$ (where $f$ is frequency and $\lambda$ is wavelength).
Question
What is the mathematical relationship between frequency ($f$) and time period ($T$)?
Answer
$f = \frac{1}{T}$
Question
How does the speed of sound ($V$) in a medium relate to its elasticity ($E$) and density ($d$)?
Answer
$V = \sqrt{\frac{E}{d}}$
Question
Why are sound waves also known as 'mechanical' or 'elastic' waves?
Answer
They require a material medium for propagation and involve the transfer of energy through particle vibrations.
Question
Which type of wave is characterized by vibrations along the direction of wave propagation, forming compressions and rarefactions?
Answer
Longitudinal wave
Question
In which media can transverse waves be formed and propagate?
Answer
Only in solids and on the surface of liquids.
Question
How does an increase in the temperature of a gas affect the speed of sound through it?
Answer
The speed of sound increases.
Question
Why does the speed of sound in air increase with higher humidity?
Answer
The density of air decreases as humidity increases.
Question
Does a change in pressure at a constant temperature affect the speed of sound in a gas?
Answer
No, because density changes in the same proportion as pressure.
Question
What is the approximate speed of sound in air at ordinary temperatures?
Answer
Approximately $330\text{ m s}^{-1}$
Question
Contrast the requirement of a medium for light waves versus sound waves.
Answer
Light waves can travel in a vacuum, whereas sound waves require a material medium.
Question
State the speed of light in a vacuum using scientific notation.
Answer
$3 \times 10^8\text{ m s}^{-1}$
Question
What is the primary requirement for the size of a reflecting surface to reflect sound waves effectively?
Answer
The size must be larger than the wavelength of the sound wave.
Question
The sound heard after reflection from a distant obstacle after the original sound has ceased is called an _____.
Answer
echo
Question
How long does the sensation of sound persist in the human ear after the stimulus ceases?
Answer
Approximately $0.1\text{ s}$
Question
What is the minimum distance required for a listener to hear a distinct echo in air (assuming $V = 340\text{ m s}^{-1}$)?
Answer
$17\text{ m}$
Question
What is the formula to calculate the distance ($d$) of an obstacle using the echo method, given sound speed ($V$) and time interval ($t$)?
Answer
$d = \frac{Vt}{2}$
Question
What term describes the effect when repeated reflections cause sound to be prolonged?
Answer
Reverberation
Question
In sonar, what does the acronym 'SONAR' stand for?
Answer
Sound Navigation and Ranging
Question
How do bats detect obstacles or prey in the dark?
Answer
By emitting ultrasonic waves and hearing the reflected echoes (sound ranging).
Question
What is the medical application of the echo method for imaging human organs called?
Answer
Ultrasonography
Question
Define 'natural vibrations'.
Answer
Periodic vibrations of a body in the absence of any external force.
Question
What happens to the amplitude of a body's vibration in a vacuum during natural vibrations?
Answer
The amplitude remains constant.
Question
Periodic vibrations of decreasing amplitude in the presence of resistive forces are known as _____ vibrations.
Answer
damped
Question
In damped vibrations, which force acts to oppose the motion and dissipate energy?
Answer
Frictional (or resistive) force
Question
Vibrations of a body that take place under the influence of an external periodic force are called _____ vibrations.
Answer
forced
Question
What occurs during the phenomenon of resonance?
Answer
A body vibrates with an increased amplitude because the external frequency matches its natural frequency.
Question
How do soldiers crossing a suspension bridge avoid causing resonance?
Answer
They are asked to break their steps so their periodic footfalls do not match the bridge's natural frequency.
Question
Why are musical instruments like the sitar provided with a hollow sound box?
Answer
To set a large volume of air into forced vibrations, increasing the loudness through a large surface area.
Question
How is a radio receiver tuned to a particular station using resonance?
Answer
The receiver circuit's frequency is adjusted to match the frequency of the incoming radio waves.
Question
Which three characteristics distinguish two sounds from one another?
Answer
Loudness, pitch (shrillness), and quality (timbre).
Question
Which physical property of a wave primarily determines the loudness of a sound?
Answer
Amplitude
Question
Define the 'intensity' of a sound wave at a point.
Answer
The amount of sound energy passing per second normally through a unit area at that point.
Question
How is loudness ($L$) related to the intensity ($I$) of a sound mathematically?
Answer
$L = K \log_{10} I$
Question
What is the unit used to measure the sound level, named after the inventor of the telephone?
Answer
decibel ($dB$)
Question
What is the reference intensity ($I_0$) for the threshold of hearing at $1\text{ kHz}$?
Answer
$10^{-12}\text{ W m}^{-2}$
Question
How does the loudness of a sound vary with the distance from the source?
Answer
Loudness varies inversely as the square of the distance.
Question
The characteristic of sound that enables one to distinguish an acute note from a grave note is called _____.
Answer
pitch
Question
Which wave property determines the pitch of a sound note?
Answer
Frequency
Question
How does a lower frequency sound affect the perceived pitch?
Answer
The sound is perceived as 'grave' or 'flat' (lower pitch).
Question
What characteristic allows a listener to distinguish between sounds of the same loudness and pitch from different instruments?
Answer
Quality (or timbre)
Question
The quality of a musical sound depends on its wave form, which is determined by the number and relative amplitudes of _____.
Answer
subsidiary (or secondary) vibrations
Question
In a C.R.O. display, what visual difference distinguishes a pure note from a musical note of the same frequency?
Answer
The pure note has a sine wave form, while the musical note has a complex wave form.
Question
What defines 'noise' in comparison to 'music'?
Answer
Noise is produced by irregular, non-periodic vibrations and is unpleasant to the ear.
Question
What is the generally accepted safe limit for the sound level for human hearing?
Answer
$0$ to $80\text{ dB}$
Question
At what sound level is sound generally considered to become 'noise pollution'?
Answer
Above $120\text{ dB}$
Question
How does increasing the tension of a stretched string affect its natural frequency of vibration?
Answer
The natural frequency increases ($f \propto \sqrt{T}$).
Question
Which wave property changes when a sound wave enters a new medium (refraction) while the frequency remains constant?
Answer
Wave speed and wavelength
Question
What is the relationship between the frequency ($f$) and length ($l$) of a vibrating air column?
Answer
Frequency is inversely proportional to the length ($f \propto \frac{1}{l}$).
Question
What term describes a sound consisting of only a single frequency?
Answer
Monotone
Question
Formula: Sound level ($L$) in decibels
Answer
$L = 10 \log_{10} \left( \frac{I}{I_0} \right)$
Question
How is a higher pitch obtained in a stringed instrument like a piano?
Answer
By using a thinner string or increasing the tension.
Question
Why is the frequency of sound considered an objective property while pitch is subjective?
Answer
Frequency is a measurable quantity of the source, while pitch depends on the listener's sensation.