Sound
Multiple Choice Questions
1. Note is a sound
(a) of mixture of several frequencies
(b) of mixture of two frequencies only
(c) of a single frequency
(d) always unpleasant to listen
Answer Answer is (a) of mixture of several frequencies Explanation: Sound is a mixture of several frequency which can be produced by vibrating objects.Show Answer
(a) sound will be louder but pitch will not be different
(b) sound will be louder and pitch will also be higher
(c) sound will be louder but pitch will be lower
(d) both loudness and pitch will remain unaffected
Answer Answer is (a) sound will be louder but pitch will not be different Explanation: Pitch depend on the frequency particular key and loudness depends on force by which key is pressed.Show Answer
(a) ultrasonic waves
(b) infrasonic waves
(c) radio waves
(d) audible sound waves
Answer Answer is (a) ultrasonic wavesShow Answer
(a) particles of medium travel from one place to another
(b) there is no moisture in the atmosphere
(c) disturbance moves
(d) both particles as well as disturbance travel from one place to another.
Answer Answer is (c) disturbance moves Explanation: Sound waves propagate by vibrating in its own position. Whereas disturbance created by vibration of particles moves from one place to another.Show Answer
(a) frequency
(b) amplitude
(c) velocity
(d) wavelength
Answer Answer is (b) amplitude Explanation: Loudness of sound is proportional to amplitude. When amplitude increase feeble sound change to loud sound.Show Answer
(a) A B
(b) B D
(c) D E
(d) A E
Fig. 12.1
Answer Answer is (b) B D Explanation: Wavelength is the distance between two consecutive troughs. In the graph half the wavelength will BD.Show Answer
(a) ultrasound
(b) infrasound
(c) audible sound
(d) none of the above
Answer Answer is (b) infrasound Explanation: It is due to infrared rays few animals sense the earthquake and they behave abnormally before earthquake.Show Answer
(a) dog
(b) bat
(c) rhinoceros
(d) human beings
Answer Answer is (c) rhinoceros Explanation: Infrasound have frequency less than $20 Hz$ and Rhinoceroses communicate using Infrasound waves of frequency of $5 Hz$ hence rhinoceros is the right answer.Show Answer
(a) intensity of sound only
(b) amplitude of sound only
(c) frequency of the sitar string with the frequency of other musical instruments
(d) loudness of sound
Answer Answer is (c) frequency of the sitar string with the frequency of other musical instruments Explanation: Artists adjust the frequencies before beginning to play an instruments because musical instruments should be tuned in with other musical instruments to produce pleasant music.Show Answer
Answer $T=2 \times 10^{6} s$ Frequency $v=\dfrac{1}{T}$ $
=10^{5} hz
$ Wavelength $\lambda \dfrac{v}{V}=5 \times 10^{5} m$Show Answer
Answer Pitch of male voice is lighter than pitch of female hence the graph a represent male voice.Show Answer
Answer Echo can be heard if the gap between the original sound and reflected sound received by the listener is around 0.1 sec. Sound Velocity $\times$ time interval $=344 \times 0.1$ $=34.4 m$ Here sound reflects from the building and then reaches the girl which is much smaller than the required distance. Hence echo cannot be heard.Show Answer
Answer Humming bees produce the sound by beating their wings and the frequency of sound they produce will be in the range of $20 Hz$ to $20000 Hz$ which is audible. On the other hand pendulum produces sound less than $20 hz$ which is below audible range and we don’t hear the sound of pendulum vibrations.Show Answer
Answer Answer is longitudinal wavesShow Answer
Answer Distance $=$ speed $\times$ time Here speed $=340 ms^{-1}$ Time $=10 s$ $=340 \times 10=3400 m$.Show Answer
Answer Angle of incidence is always equal to the Angle of reflection Angle of Incidence $=90^{\circ}-50^{0}=40^{\circ}$ Angle of reflection $=$ angle of incidence $=40^{\circ}$ Hence angle $x$ is $40^{\circ}$Show Answer
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Answer
Ceiling and wall behind the stage of good conference halls or concert halls made curved to ensure the reflected sound equally to all the audience.
Long Answer Questions
18. Represent graphically by two separate diagrams in each case
(i) Two sound waves having the same amplitude but different frequencies?
(ii) Two sound waves having the same frequency but different amplitudes.
(iii) Two sound waves having different amplitudes and also different wavelengths.
Answer (a) Two sound waves having same amplitude but different frequencies.
(b) Two sound waves with same frequency and different amplitudes.
(c) Two sound waves having varying amplitudes and different wavelengths.
Show Answer
(i) wavelength when frequency is $256 Hz$.
(ii) frequency when wavelength is $0.85 m$
Answer Relationship between Sound speed, wavelength and frequency Speed $=\dfrac{\text{ Distance }}{\text{ Time }}$ $V=\dfrac{\text{ Wavelength }}{\text{ Time }}$ $V=$ $\dfrac{\text{ Wavelength } \times 1}{\text{ time }}$ Frequency $=\dfrac{1}{\text{ time }}$ $V=$ wavelength $\times$ frequency 1) Wavelength $=\dfrac{\text{ speed }}{\text{ frequency }}$
$=\dfrac{340}{256}$ $=1.32$ mType equation here. 2) Frequency $=$ speed $/$ wavelength $\dfrac{\text{ speed }}{\text{ wavelength }}$ $=\dfrac{340}{0.85}$ $=400 HZ$Show Answer
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