Team Quanta gladly presents all possible short questions of BS Physics book Waves and Oscillation Chapter#03: Beats and Polarization.
Q.1 Sound waves can be used to measure the speed at which the blood flows in arteries and veins. Explain How?
Answer: Velocity measurement of blood flow in arteries and veins is based on Doppler’s effect. By sending a sound signal through an astray and measuring the change in its frequency, one can find easily the speed of the blood through which the sound was passed.
Q.2 Why does sound not travel through a vacuum?
Answer: As sound waves are mechanical waves and mechanical waves require medium for their propagation, for this reason sound does not travel through a vacuum.
Q.3 Does your singing really sound better in a shower? Is so what are the physical reasons?
Answer : Your shower works like a low-tech sound mixer that modifier your voice in three different ways thus improving your sound.
- Volume – sound reflect back and forth between the sound intensity.
- Reverberation – reflected sounds cause a prolonged effect of listening.
- Bass boast – shower act like a closed box due to which resonance make some frequencies to be amplified.
Q.4 Explain tuning of musical instruments by beat phenomenon.
Answer: When two musical instruments, one of known frequency and other of unknown having slightly different frequencies (beat) are sounded together. If the known frequency instrument is so adjusted till the frequency difference between them becomes zero (f1-f2) no. of beats per second will become zero. Then due to resonance other instruments can be tuned.
Q.5 Define beat and beat frequency?
Answer: The intensity of sound is rise and fall, this rise and fall of sound is called beats. The difference it between the frequencies of the sound is called beat frequency. For example if one sound has 30Hz and other has 32Hz then the beat frequency,
$$f_2-f_1=n\ \ ,\ \ \ 32-30\ \ ,\ \ \ =2Hz$$
Q.6 What experimental evidence is there for assuming that the speed of sound in air is the same for all wavelengths?
Answer: The speed of a sound in a medium depends upon the nature of the medium. It is independent of the frequency of the wave. All sound waves, whether of low frequency or high frequency travel through a medium at the same speed.
Q.7 How can a sound wave travel down an organ pipe and be reflected at its open end? It seems there is nothing there to reflect it.
Answer: The density of air at the open end of the organ pipe is smaller than the density of air inside the pipe. Therefore, when sound waves reach the open end, they experience a change of medium and hence undergo reflection.
Q.8 The resonant frequencies of wind instrument rise as an orchestra warms up. Explain why.
Answer: As a wind instrument w arms up, the density of air inside the instrument decreases. This increases the speed of the sound in the orchestra. Since frequency of a wave is directly proportional to its speed, that is why the frequency of sound emitted by orchestra increases.
Q.9 Define Doppler effect.
Answer: An increase or decrease in the frequency of sound, light or other waves, as the observer and source mover towards, or away from each other. The effect causes the sudden change in pitch, noticeable in the passing siren as well as red shift seen by astronomers.
Q.10 When you strike one prong of the tuning fork the other prong also oscillates, even if the bottom end of the fork is clamped formally in a vise. How can this happen? That is how does the second prong gets the world that somebody has strike the first prong?
Answer: Since both prong of the tuning fork are identical, they hence the same natural frequencies. When one prong vibrates the other comes in resonance with the first and also starts vibrating with large amplitude.
Q.11 Explain how a stringed instrument is tuned?
Answer: String instrument is tuned by tightening or losing the sting which adjust the beat frequency. When we change the length then the frequency or pitch of the sound is produced.
Q.12 You wish to tune the note A3 on a piano to its proper frequency of 220Hz. You have available a tuning fork whose frequency is 440Hz. How should you proceed?
Answer:
No of beats = n = 3
Frequency of for =
Then the string frequency
$$f_2-f_1=\ \pm n$$
$$f_2=f_{1\pm n}$$
$$f_{2\ }=440\pm3$$
$$=440+3\ ,\ 440-3$$
$$f_2=443Hz,\ 437Hz$$
