64 Questions
What is the condition for an echo to be produced?
If sound is reflected back from an obstacle to the observer in such a way that he/she hears it distinctly as a repetition of the original sound.
Why are the walls of auditoriums and cinema halls covered with soft materials like curtains?
To decrease the reverberation time by absorbing sound, rather than reflecting it.
What is the formula to determine the speed of sound, given the distance and echo time?
v = 2s / t
What is the application of echo in determining the depth of an ocean?
Using sonar, the echo time is measured, and the speed of sound in seawater is used to calculate the depth.
Why does sound not reflect off soft surfaces like cloth and rubber?
Because they absorb sound, rather than reflecting it.
What is the significance of the equation v = 2s / t in the context of echo?
It determines the speed of sound, given the distance and echo time.
What is the role of echo in determining the velocity of sound in air?
By measuring the distance and echo time, the velocity of sound can be calculated.
What is the relevance of the distance between the source and obstacle in echo formation?
It determines the total distance travelled by the sound wave, which is 2s.
What is the principle used in radar to determine the elevation and speed of an airplane?
The difference in frequency between the transmitted and reflected radio waves
How does SONAR calculate the speed of an approaching submarine?
By measuring the frequency of the reflected sound waves
What is the purpose of Doppler echocardiography?
To examine the heart and determine the speed and direction of blood flow
What is the frequency detected by the detector when a train moving towards it at 30m/s blows a 305Hz horn?
350Hz
What is the frequency detected by the detector when a train moving away from it at 30m/s blows a 305Hz horn?
280.3Hz
What is the principle demonstrated in the Doppler effect using a tuning fork?
The change in pitch due to the motion of the source
What type of wave is used in radar technology?
Radio wave
What is the purpose of measuring the frequency of reflected waves in SONAR?
To determine the speed and direction of an object
If the intensity of sound at a distance of 40m from the source is 4 × 10^-6 W/m^2, what will be the intensity at a distance of 80m?
1 × 10^-6 W/m^2
What is the power transmitted by a sound wave of intensity 4 × 10^-3 W/m^2, when you are 5m away from the source?
25 × 10^-3 W
What is the Doppler Effect, and what types of waves does it affect?
The Doppler Effect is the variation in the pitch of a sound due to the relative motion between a source of sound and a listener. It affects not only sound waves but also light and radio waves.
What happens to the frequency of sound waves when the source is approaching an observer?
The frequency of sound waves appears to increase, resulting in a higher pitch.
What is the relationship between the frequency of sound waves and the motion of the source?
When the source and observer are in relative motion, the frequency of the wave noted by the observer appears to be different from the true frequency.
What is the difference between the frequency of sound waves reaching an observer's ear and the frequency of the source?
When the source, medium, and observer are at rest, the frequency of sound reaching the observer's ear is the same as the frequency of the source.
What happens to the frequency of sound waves when the source is moving away from an observer?
The frequency of sound waves appears to decrease, resulting in a lower pitch.
How does the Doppler Effect relate to the concept of refraction?
The Doppler Effect does not directly relate to the concept of refraction, which is the bending of waves as they pass from one medium to another.
Sound waves are reflected off ______ surfaces like glass and wood.
hard
Soft surfaces like ______ and rubber absorb sound.
cloth
The time taken for sound to die away in a building is called the ______ time.
reverberation
The equation v = 2s / t is used to determine the ______ of sound at a given temperature.
speed
Echoes have many uses, including the determination of the ______ of sound in air.
velocity
Sonar devices use ______ waves to determine the depth of oceans or seas.
underwater sound
The principle of echo is used in ______ to determine the elevation and speed of an airplane.
radar
The ______ effect is a change in frequency observed when the source of sound is moving relative to the observer.
Doppler
Radar is a device that transmits and receives _______ waves.
radio
SONAR uses _______ waves to detect submarines.
sound
Doppler echocardiography uses _______ technology to examine the heart.
Doppler ultrasonography
The Doppler effect is demonstrated using a _______ fork.
tuning
The frequency of the reflected waves is measured to calculate the speed of the _______.
submarine
Radar sends high frequency _______ waves towards an airplane.
radio
The difference in frequency is used to determine the elevation and _______ of an airplane.
speed
Sound waves generated from a ship fitted with SONAR are transmitted in _______ towards an approaching submarine.
water
A loudspeaker radiates sound uniformly in all ______ directions.
all
If the intensity of the sound at a distance of 40m from the source is 4 × 10^-6 w/m^2, what will be the intensity at a distance of ______m?
80
The Doppler Effect is the variation in the ______ of a sound due to the relative motion between a source of sound and a listener.
pitch
As the ambulance is moving away from you, the sound waves ______ further apart resulting in a lower pitch.
spread
The frequency of sound reaching a listener's ear will be the same as the frequency of the source when the source of sound, the medium and the listener are all at ______.
rest
The Doppler Effect works not only for sound but also for ______ and radio waves.
light
When the source and the observer are in relative motion, the frequency of the wave noted by the observer appears to be different from the true ______ frequency.
source
The intensity of the sound wave of a beetle is 4 × 10^-3 w/m^2, when you are ______m away from it.
5
The phenomenon of variation of the frequency of the sound heard by the relative motion of the source or the listener is known as ______ effect.
Doppler
When the source and observer are relatively at rest with respect to each other, the frequency heard by the observer is equal to the ______ frequency produced by the source.
actual
When a listener is moving towards the stationary source, the apparent frequency is given by the equation fL = fs [(1 + VL)/V].
sound
Sound waves with frequency above the audio range are called __________
ultrasound
The frequency of the ______ received by the listener when the source of ______ is moving towards a stationary listener is given by the equation fL = fs [(V + Vs)/(V - Vs)].
sound
The minimum intensity level at which sound waves of different frequencies can be heard is called the __________ of hearing.
threshold
The maximum intensity level for audible sounds is called the __________ of pain.
threshold
In Case III, a listener moving away from the stationary source, the frequency of the ______ received by the listener is given by the equation fL = fs [(1 - VL)/V].
sound
The ______ effect is illustrated in Figure 32.
Doppler
The range of __________ frequencies is from 20 Hz to 20,000 Hz.
audio
The speed of sound in air at 25°C is approximately __________ m/s.
343
When the source of sound is moving towards a stationary listener, the frequency of the sound produced by the source (fs) and the frequency of the sound received by the listener (fL) are related by the equation fL = fs [(V + Vs)/(V - Vs)].
speed
The human ear can just detect sound waves of intensity __________ W/m².
10⁻²
The apparent frequency due to ______ effect for different cases can be deduced as follows.
Doppler
The wavelength of a __________ sound wave in a bar of iron can be calculated using the equation λ = v / f.
10KHz
The intensity of sound decreases by a factor of __________ if the distance from a point source is tripled.
9
Study Notes
Radar
- Radar devices transmit and receive radio waves to detect objects like airplanes
- Reflected radio waves are detected by the receiver to determine the elevation and speed of the airplane
Sonar (Sound Navigation and Ranging)
- SONAR uses sound waves to detect submarines underwater
- Frequency of reflected waves is measured to calculate the speed of the submarine
Doppler Echocardiogram
- Doppler echocardiography examines the heart using high-frequency sound waves
- Doppler technology determines the speed and direction of blood flow using the Doppler effect
Doppler Effect
- The Doppler effect is the variation in pitch of a sound due to relative motion between a source of sound and a listener
- The frequency of the sound heard by the listener is not the same as the source frequency when in motion relative to each other
- Applies to light and radio waves as well, with important applications in medicine and technology
Reflection of Sound
- Sound waves can be reflected off hard surfaces like glass and wood, but not soft surfaces like cloth and rubber
- Echoes can be used to determine the velocity of sound in air and the depth of oceans or seas using sonar
Applications of Reflection of Sound
- Determining the velocity of sound in air
- Determining the depth of oceans or seas using sonar
- Measuring the intensity of sound waves
Intensity of Sound Waves
- Intensity of sound waves decreases with distance from the source
- Example: intensity of sound at 40m and 80m from a loudspeaker
Radar and Sonar
- Radar is a device that transmits and receives radio waves to detect and determine the elevation and speed of an object, such as an airplane.
- Sonar (Sound Navigation and Ranging) uses sound waves to detect and determine the speed of an object, such as a submarine, by measuring the frequency of the reflected waves.
Doppler Effect
- The Doppler effect is the variation in the pitch of a sound due to the relative motion between a source of sound and a listener.
- The effect occurs when a source of sound and a listener are in motion relative to each other, resulting in a change in the frequency of the sound heard by the listener.
- The Doppler effect is used in medicine and technology, and works not only for sound but also for light and radio waves.
Applications of Reflection of Sound
- Echoes can be used to determine the velocity of sound in air by measuring the distance between the source and obstacle, and the echo time.
- Echoes can be used to determine the depth of an ocean or sea using a device called sonar.
- Sound waves are reflected off hard surfaces like glass and wood, but not off soft surfaces like cloth and rubber, which absorb sound.
Intensity of Sound
- The intensity of sound is measured in watts per square meter (W/m²).
- The intensity of sound decreases with distance from the source.
- The range of audio frequencies is from 20 Hz to 20,000 Hz.
Threshold of Hearing and Pain
- The threshold of hearing is the minimum intensity level at which sound waves of different frequencies can be heard, typically around 5 dB.
- The threshold of pain is the upper intensity level for audible sounds, typically around 130 dB.
- The threshold of hearing and pain vary from person to person, depending on age, the shape and health of the ear.
Exercises and Calculations
- The speed of sound at 25°C is 343 m/s.
- The wavelength of sound in air at 30°C can be calculated using the formula λ = v × T, where v is the speed of sound and T is the period.
- The distance between a man and a cliff can be calculated using the formula d = v × t, where v is the speed of sound and t is the time taken for the sound to travel to the cliff and back.
- The sound energy incident on an eardrum can be calculated using the formula E = I × A, where I is the intensity of sound and A is the area of the eardrum.
Learn about radar and sonar technology, including how they work and their applications in detecting and tracking objects.
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