Quick Review Flashcards - Click to flip and test your knowledge!
Question
What are the two primary ways energy can be transferred from one place to another?
Answer
By the transfer of matter (e.g. throwing a ball) or by wave motion.
Question
Waves that require a material medium for their transmission are called _____ waves.
Answer
mechanical
Question
Which type of waves can be transmitted through a vacuum?
Answer
Electromagnetic waves (e.g. light waves, X-rays, radio waves).
Question
In a mechanical wave, do the particles of the medium travel along with the disturbance?
Answer
No, the particles vibrate about their mean positions and transfer energy to neighbouring particles.
Question
What two properties of a medium determine the speed of propagation of a disturbance within it?
Answer
Elasticity and density.
Question
Term: Amplitude ($a$)
Answer
Definition: The maximum displacement of a particle of the medium on either side of its mean position. SI unit: metre ($m$).
Question
Term: Time period ($T$)
Answer
Definition: The time taken by a particle of the medium to complete one full vibration. SI unit: second ($s$).
Question
Term: Frequency ($f$)
Answer
Definition: The number of vibrations made by a particle of the medium in one second. SI unit: hertz ($Hz$).
Question
Formula: Relationship between frequency ($f$) and time period ($T$)
Answer
$f = \frac{1}{T}$
Question
The frequency of a wave is determined by the frequency of its _____, not the medium's properties.
Answer
source
Question
Term: Wavelength ($\lambda$)
Answer
Definition: The distance travelled by a wave in one time period of vibration of a particle of the medium. SI unit: metre ($m$).
Question
In a longitudinal wave, the distance between two consecutive compressions or rarefactions is equal to one _____.
Answer
wavelength ($\lambda$)
Question
In a transverse wave, the distance between two consecutive crests or troughs is equal to one _____.
Answer
wavelength ($\lambda$)
Question
Term: Wave velocity ($V$)
Answer
Definition: The distance travelled by a wave in one second. SI unit: $m\ s^{-1}$.
Question
Formula: Relationship between wave velocity ($V$), frequency ($f$), and wavelength ($\lambda$)
Answer
$V = f \lambda$
Question
Which graph shows the variation of displacement with time for a single particle at a fixed position?
Answer
Displacement-time graph.
Question
Which graph provides a 'snapshot' of the displaced positions of all particles in a medium at a specific instant?
Answer
Displacement-distance graph.
Question
In a _____ wave, particles vibrate perpendicular to the direction of wave propagation.
Answer
transverse
Question
The position of maximum upward displacement in a transverse wave is called a _____, while maximum downward displacement is a _____.
Answer
crest; trough
Question
Why can transverse waves not be produced inside liquids or gases?
Answer
Because liquids and gases do not possess the necessary rigidity to support transverse motion.
Question
In a _____ wave, particles vibrate in the same direction as the wave propagation.
Answer
longitudinal
Question
Longitudinal waves consist of alternating regions of high pressure called _____ and low pressure called _____.
Answer
compressions; rarefactions
Question
At which point in a longitudinal wave are the density and pressure of the medium at their maximum?
Answer
Compression.
Question
Sound waves in air are classified as _____ mechanical waves.
Answer
longitudinal
Question
What is the physical cause of sound?
Answer
Vibrations of a body.
Question
Which experiment demonstrates that sound requires a material medium and cannot travel through a vacuum?
Answer
The Bell jar experiment.
Question
Why can one not hear sound on the Moon?
Answer
Because the Moon has no atmosphere (medium) for sound to travel through.
Question
Identify the requisite: For a medium to propagate sound, it must be _____ so particles return to their mean positions after displacement.
Answer
elastic
Question
Identify the requisite: A medium must have _____ so its particles can store mechanical energy.
Answer
inertia
Question
Formula: Speed of sound ($V$) in a medium with modulus of elasticity ($E$) and density ($\rho$)
Answer
$V = \sqrt{\frac{E}{\rho}}$
Question
Why was Newton's calculated speed of sound in air ($279.5\ m\ s^{-1}$) lower than the experimental value?
Answer
He incorrectly assumed sound propagation in air is an isothermal process.
Question
Laplace corrected the speed of sound formula by assuming that sound propagation in gas is an _____ process.
Answer
adiabatic
Question
Formula: Laplace's corrected speed of sound in a gas
Answer
$V = \sqrt{\frac{\gamma P}{\rho}}$
Question
How does the speed of sound generally compare across the three states of matter?
Answer
Solids $>$ Liquids $>$ Gases.
Question
How is the speed of sound in a gas related to its density ($\rho$)?
Answer
It is inversely proportional to the square root of the density ($V \propto \frac{1}{\sqrt{\rho}}$).
Question
How does the speed of sound in a gas change with temperature ($T$)?
Answer
It is directly proportional to the square root of the absolute temperature ($V \propto \sqrt{T}$).
Question
Formula: Speed of sound in air ($V_t$) at temperature $t$ (in Celsius) relative to $V_0$
Answer
$V_t = V_0 + 0.61t$
Question
How does the presence of humidity affect the speed of sound in air?
Answer
It increases the speed because humid air is less dense than dry air.
Question
If the air pressure is doubled at a constant temperature, what happens to the speed of sound?
Answer
The speed of sound remains unchanged.
Question
Does the speed of sound depend on its frequency or wavelength?
Answer
No, the speed of sound is independent of both frequency and wavelength.
Question
The speed of light in air is approximately $3 \times 10^8\ m\ s^{-1}$, which is about _____ times faster than the speed of sound.
Answer
one million ($10^6$)
Question
Why is the sound of thunder heard after the lightning flash is seen, even though they occur simultaneously?
Answer
Light travels much faster ($3 \times 10^8\ m\ s^{-1}$) than sound ($330\ m\ s^{-1}$).
Question
What is the range of sound frequencies audible to a normal human ear?
Answer
$20\ Hz$ to $20,000\ Hz$ (or $20\ kHz$).
Question
Term: Infrasonic sound
Answer
Definition: Sound waves with frequencies below $20\ Hz$.
Question
Term: Ultrasonic sound (or Ultrasound)
Answer
Definition: Sound waves with frequencies above $20,000\ Hz$.
Question
Which animal can hear the highest frequency range, reaching up to $100\ kHz$?
Answer
Bats.
Question
List two properties of ultrasound that make it more useful than ordinary audible sound.
Answer
It carries very high energy and travels in a well-defined straight path (high directivity).
Question
How do bats use ultrasound to navigate and hunt?
Answer
They produce ultrasound and judge the distance of obstacles or prey by hearing the reflected echoes.
Question
Term: Echo cardiography
Answer
Definition: The use of ultrasound imaging to obtain an image of the heart.
Question
In medicine, ultrasound is used to break kidney _____ into fine grains.
Answer
stones
Question
What does the acronym SONAR stand for?
Answer
Sound Navigation and Ranging.
Question
Concept: Ultrasonic vs Supersonic
Answer
Definition: Ultrasonic refers to frequency above $20\ kHz$; Supersonic refers to speeds greater than the speed of sound.
Question
Concept: Infrasonic vs Subsonic
Answer
Definition: Infrasonic refers to frequency below $20\ Hz$; Subsonic refers to speeds less than the speed of sound.
Question
Which property of ultrasound allows it to be used for detecting defects in metals?
Answer
It passes through metals but is reflected back if it hits a crack or cavity.
Question
How is ultrasound used for cleaning minute objects like watch parts?
Answer
The parts are placed in a solution where ultrasonic waves create high-frequency vibrations that remove dirt.
Question
What animal produces infrasonic sounds with frequencies less than $20\ Hz$?
Answer
Elephants (or whales).
Question
Under what condition does the speed of sound increase due to wind?
Answer
When the wind is blowing in the same direction as the sound propagation.
Question
Why is sound heard much sooner through a steel railway track than through the air?
Answer
Sound travels significantly faster in solids (steel $\approx 5100\ m\ s^{-1}$) than in gases (air $\approx 330\ m\ s^{-1}$).
Question
Which factor(s) among pressure, amplitude, and frequency do NOT affect the speed of sound in a gas?
Answer
None of them affect the speed of sound.
Question
What is the approximate speed of sound in water at $0^{\circ} C$?
Answer
$1450\ m\ s^{-1}$.