1. What is the frequency range of audible sound?
The range of audible frequencies is 20Hz to 20,000Hz.
2. What are ultrasonic waves?
Sounds waves of frequencies beyond 20 kHz are called ultrasonic waves.
3. List any six uses of ultrasonic waves?
· Study of ultrasonic waves gives information about its physical properties like elasticity, configuration of atoms etc.
· They are used in the manufacturing of alloys, for mixing of immiscible and to manufacture emulsion for photographic films.
· They are used in the dry cleaning of clothes to remove dirt.
· They can be used to detect cracks and flaws in metal molding.
· They are used for welding, local heating and drilling small holes in hard materials.
· Ultrasonic waves serve as insect repellants and are used for sterilization purposes.
· They are used to cure neuralgic and rheumatic pains.
· Surgical instruments vibrating at ultrasonic frequencies are used in bloodless surgery.
· They can be used to break gallstones and stones in the kidney
4. What is SONAR? How does it work?
a) Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.
b) It can be used to find the distance of an object in water and works as follows.
· SONAR is installed in a boat or ship. It consists of a transmitter and a receiver
· The transmitter produces and transmits ultrasonic waves. These waves travel through water until they strike an object, reflect and return to the sonar.
· The time interval between transmission and reception‘t’ recorded. The detector converts the reflected waves into electrical signals and interprets them.
· If ‘v’ is the velocity of sound through water, then the distance of the object is given by d = vt/2
5. Using sonar, ultrasonic waves are emitted at the ocean water surface. The ocean bottom reflects these waves. If the time interval between the emission of the waves and the detection of the reflected waves is 3.5 seconds, find the depth of the ocean.
Time ‘t’ between the emission of the waves and detection of reflected waves = 3.5 seconds
Velocity of sound in water ‘v’ = 1.5km/second
Distance of the object = vt/2
= 3.5 x 1.5/2 = 2.625km
6. What is an ultrasonic scanner?
Ultrasonic scanners are instruments that use ultrasonic waves for getting image of internal organs of human body.
7. Write a note on the medical applications of ultrasonic waves
· They can be directed towards specific area of the body. The waves get reflected and provide information about the change in the density of tissues.
· They are used in scanning, as they are less harmful than X-rays.
· They are used to obtain information about the internal organs of a body and more so for fluid filled organs like bladders, kidneys and ovaries.
· It is used in ECG for diagnosing heart diseases and in foetus examination during pregnancy.
8. Explain Doppler Effect with a suitable example.
· Imagine, you are standing in a railway platform and a train is reaching you of moving towards you.
· The frequency of sound increases as it reaches you.
· You stand in the same position, and if the train leaves the platform, the frequency of sound again decreases.
· Similar observations are noticed when you are moving and the source is stationery.
· This change in the frequency due to the relative motion of the observer and the source.
· This principle of apparent change in frequency is called Doppler Effect.
9. Mention three applications of Doppler Effect.
Doppler Effect of sound can be used to
· Determine the velocity of submarines
· Detect velocities of vehicles crossing speed limits
· Track artificial satellites.
10. Write a note on application of Doppler Effect in astrophysics?
· Doppler’s effect is found useful in the study of binary stars, Saturn rings, galaxies etc.
· It is used to estimate the speed of stars, galaxies and rotation of sun’s disc.
· The red shift observes in the spectrum of the galaxies helps to determine the velocity of the source.
ADDITIONAL IMPORTANT QUESTIONS
1. How is sound produced?
Sound produced by the vibration of a body
2. How is sound propagated?
Sound is propagated in the form of a wave
3. How do we hear sound?
Sound is produced by the vibrations of a body. When these vibrations are registered in our brain, we hear sound
4. What is a wave? How is it described?
a) A wave is a periodic disturbance propagating through a medium, carrying energy.
b) It is described in terms of its frequency (f), wavelength (l) and velocity (v)
5. Write the equation for a wave and indicate the notations used.
The equation for a wave is v = fl, where is the frequency, l is the wavelength and v is the velocity
6. What is audible range?
The range of frequencies that can be heard by normal human beings is called audible range.
7. What is ultrasonic sound? What is their range?
a) Sounds of frequencies beyond 20 kHz are called ultrasonic sounds.
b) Their frequency ranges from 20 kHz to 5 x 105 kHz.
8. How are the speeds of the two related audible range ultrasonic range?
Both are equal.
9. What is infrasonics? How does it differ from supersonics?
a) Infrasonics refers to sounds of frequencies lesser than 20Hz.
b) Supersonics refers to waves of velocities greater than that of sound.
10. Why do ultrasonic waves have high energy?
Ultrasonic waves have energy because of their high frequency.
11. What is a radar gun?
Radar gun is a device used to detect the vehicles crossing the speed limit.
12. What is SONAR? Briefly explain one of its uses with an example.
· Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.
· It can be used to find the distance of objects under water
· The ultrasound signal sent by sonar takes 3 seconds to return.
· The velocity of sound in water is 1.5km/second.
· The distance traveled by the signal
= 1.5 x 3 = 4.5km
· Hence, the distance of the object
= 4.5/2 = 2.25km
13. Who invented Sonar? Why?
Paul Langevin invented sonar. It was result of the inspiration by titanic disaster.
14. What is echo ranging?
It is technique of finding the distance of under water objects using sonar.
15. Why are ultrasonic waves preferred for X-rays? Name the best-known application of ultrasonics in medicine.
a) Ultrasonic waves are preferred because they are less harmful than X-rays.
b) Examination of foetus during pregnancy is the best-known application of ultrasonics in medicine.
16. What is Doppler Effect? What changes are observed in the case of light waves?
a) Doppler Effect is the apparent change in frequency of wave motion due to the relative motion between the source and the observer.
b) Doppler Effect in light can be observed only in celestial bodies or atomic sources that are moving with high velocities. In the case of light waves, there is a shift in the wavelength of light emitted by celestial bodies.
17. What is red shift?
The shift in the color of the light towards the red end of the spectrum when a source emits light of particular wavelength and moves away from us are called the re shift.