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Thursday, 14 November 2013

F.Sc Notes: Physics XI: Chapter 08 Waves Exercise Short Questions:

FSc Notes: Physics XI: Chapter 08 Waves Exercise Short Answer:


Question 8.1 What features do longitudinal waves have in common with transverse waves?
Answer 8.1
Common features between longitudinal and transverse waves.
  1. They produce disturbance in the medium in which they are traveling.
  2. Transport energy from one place to another.
  3. The equation v = f λ is valid for both waves.


Question 8.2 The five possible waveform obtained, when the output from a microphone is fed into the Y-input of the cathode ray oscilloscope, with the time base on, are shown in fig8.23 (on book). These waveform are obtained under the same adjustment of the cathode ray oscilloscope controls. Indicate the waveform.
a. which trace represents the loudest note?
b. which trace represents the highest frequency?
Answer 8.2
Loudness of sound depends on the intensity of sound which is directly related with the square of amplitude of the waves. Hence fig b represents the loudest note. Trace b has the highest frequency as the wavelength is small than other waves.


Question 8.3 Is it possible for two identical waves traveling in the same direction along a string to give rise to a stationary wave?
Answer 8.3 No
, there is no possibility for two waves traveling in the same direction along a string to give rise to a stationary wave. As stationary wave is produced by the superposition of two identical waves traveling in opposite direction.


Question 8.4 A wave is produced along a stretched string but some of its particles permanently show zero displacement. What type of wave is it?
Answer 8.4
The wave in which some of its particles permanently show zero displacement is known as stationary wave and these zero displacement maximum tension points are known as nodes.


Question 8.5 Explain the terms crest, trough, node and anti nodes.
Answer 8.5 Crest:
The portion of wave above mean position in a traverse wave is called crest.
Trough: The portion of wave below mean position in a traverse wave is called trough.
Node: Points having zero amplitude in a stationary wave is called node.
Anti nodes: Points having maximum amplitude in a stationary wave is called anti nodes.


Question 8.6 Why does a sound travel faster in solids than in gases?
Answer 8.6
In the relation v = √ (E / ρ) ‘E’ Elasticity of the medium is directly proportional to velocity of sound    its value is greater for solids than in gases. The effect of density, ρ is very less as compared to E. The ratio of  (E / ρ) is greater for solid than gases, so sound travel faster in solids then in gases.


Question 8.7 How are the beats useful in tuning musical instruments?
Answer 8.7
A new instrument is tuned as it is played with the standard musical instruments. They are sounded together thus beats are produced. The frequency of the new instrument is changed until the resonance occurs.


Question 8.8 When two notes of frequency f1 and f2 are sounded together, beats are formed if f1>f2. What will be the frequency of beats?
  1. f1+f2
  2. 1/2(f1+f2)
  3. f1-f2
  4. ½(f1-f2)
Answer 8.8 Since we know that no of beats per second is equal to the difference between the frequencies of the tuning forks. Hence option iii) f1-f2 is correct.

Question 8.9 As a result of distant explosion, an observer senses a ground tremor and then hears the explosion. Explain the time difference.
Answer 8.9
Sound waves travel faster in solids than in air. The sound waves produced by the explosion travel from two paths. One through ground reaches faster than traveling through air. This is the reason for time difference.


Question 8.10 Explain why sound travels faster in warm air than in cold air.
Answer 8.10
                        v ∝ √T  and  v = √ (γ P / ρ)
The speed of sound varies directly as the square root of absolute temperature and inversely to the square root of density of medium. As the temperature of air increases, the pressure increases and density decreases. So, speed of sound increases in warm air.


Question 8.11 How should a sound source move with respect to an observer so that the frequency of its sound does not change?
Answer 8.11
Both the source and the observer should not move so their relative speed be zero. From Doppler Effect, Then there will be no change in the frequency of its sound.

Written By: Asad Hussain

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