- (a) stretched strings
- (b) stretched membranes
- (c) air columns
- (d) metal plates
Answer:
(d) metal plates
- (a) only if no moisture is present
- (b) if particles move from one place to another
- (c) if both particles and disturbance move
- (d) if disturbance moves
Answer:
(d) if disturbance moves
Particles vibrate about mean position; disturbance travels.
- (a) wax
- (b) vacuum
- (c) water
- (d) empty vessel
Answer:
(b) vacuum
Sound cannot travel through vacuum.
- (a) sea water
- (b) ground glass
- (c) dry air
- (d) human blood
Answer:
(b) ground glass
- (a) liquids
- (b) gases
- (c) solids
- (d) vacuum
Answer:
(c) solids
- Sound is a longitudinal mechanical wave and requires a material medium.
- Number of vibrations produced in one second is called frequency.
- Velocity of sound in solids is greater than in air.
- Vibrations of objects produce sound.
- Loudness is proportional to square of the amplitude of vibration.
- Stethoscope is used for listening to sounds inside body.
- Repeated reflection causing persistence of sound is called reverberation.
| List I | List II |
|---|---|
| Tuning fork | Production of sound |
| Sound | Longitudinal wave |
| Compressions | Region of maximum density |
| Amplitude | Maximum displacement from equilibrium |
| Ultrasonics | Frequency greater than 20,000 Hz |
Answer:
Sound travels faster through iron.
Reason:
Speed of sound is maximum in solids because particles are closely packed.
Answer:
Frequency.
Definition:
Frequency is number of vibrations produced in one second.
Unit:
Answer:
Speed greater than speed of sound in air is called supersonic speed.
(approximately at room temperature)
Answer:
- Vibrating object sets nearby particles vibrating.
- Vibrating particles transfer energy to neighbouring particles.
- Compressions and rarefactions travel through medium.
- Sound finally reaches ears.
Answer:
No.
Reason:
Moon has no atmosphere, hence no material medium for sound transmission.
Compression
When vibrating body moves forward:
- particles crowd together
- pressure increases
This region is called:
Compression
Rarefaction
When vibrating body moves backward:
- particles spread apart
- pressure decreases
This region is called:
Rarefaction
Procedure
- Take two long identical tubes.
- Place them near reflecting wall.
- Place ticking clock near one tube.
- Listen through second tube.
- Adjust tube positions for maximum sound.
Observation
Measured angles satisfy:
Conclusion
Laws of reflection of sound are verified.
- Angle of incidence = angle of reflection
- Incident sound, reflected sound and normal lie in same plane
Cleaning
Used to remove tiny dust particles from delicate objects.
Industry
Used to detect cracks in metal blocks.
Medicine
(i) Echocardiography
Ultrasound used to study heart.
(ii) Kidney Stones
Ultrasonic waves break stones into smaller pieces.
SONAR
Working
- Ultrasonic waves transmitted through water.
- Waves strike object and reflect back.
- Detector receives echo.
- Time interval measured.
Distance:
Where:
- (d) = distance
- (v) = speed of sound
- (t) = total time
This method is called:
Echo-ranging
Given:
Frequency means vibrations per second.
In one minute:
Answer:
Correction made:
Unit should be “vibrations”, not “Hz”.
Given:
Time for Stone to Fall
Using:
Time for Sound to Travel Upward
Total Time
Answer:
Vibrations of Tuning Fork
Observation:
Tuning fork vibrates when struck.
Conclusion:
Sound is produced due to vibrations.
Longitudinal Wave Using Spring
Observation:
- Some turns crowd together
- Some turns spread apart
Conclusion:
- Crowded regions → compressions
- Spread regions → rarefactions
Sounds from Musical Instruments
Observation:
Different instruments produce different sounds.
Sound Characteristics:
- Amplitude
- Wavelength
- Frequency
- Pitch
- Loudness
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