Question 1

Question 1Two waves of the same pitch have amplitudes in the ratio 1:3. What will be the ratio of their:(i) loudness(ii) pitch?

Accepted Answer

(i) Loudness (L) ∝ [amplitude (a)]2Ratio of loudness =L1L2=(a1)2(a2)2=(1)2(3)2=19\dfrac{	ext{L}_1}{	ext{L}_2} = \dfrac{(	ext{a}_1)^2}{(	ext{a}_2)^2} = \dfrac{(1)^2}{(3)^2} = \dfrac{1}{9}L2​L1​​=(a2​)2(a1​)2​=(3)2(1)2​=91​So L1 : L2 = 1 : 9.(ii) Frequency remains the same if the pitch remains unchanged.pitch of 1st wavepitch of 2nd wave=11=1:1\dfrac{	ext{pitch of 1st wave}}{	ext{pitch of 2nd wave}} = \dfrac{	ext{1}}{	ext{1}} = 1:1pitch of 2nd wavepitch of 1st wave​=11​=1:1So pitch will be 1 : 1.

Question 2

Question 2Two waves have frequencies 256 Hz and 512 Hz, but same amplitude. Compare their:(i) loudness, and(ii) pitch.

Accepted Answer

(i) Since amplitude of two waves are same so loudness of both the waves will be same.amplitude of 1st waveamplitude of 2nd wave=11=1:1\dfrac{	ext{amplitude of 1st wave}}{	ext{amplitude of 2nd wave}} = \dfrac{	ext{1}}{	ext{1}} = 1:1amplitude of 2nd waveamplitude of 1st wave​=11​=1:1So, loudness of first wave : loudness of second wave = 1:1.(ii) Frequency determines the pitch of the sound.frequency of 1st wavefrequency of 2nd wave=256512=12=1:2\dfrac{	ext{frequency of 1st wave}}{	ext{frequency of 2nd wave}} = \dfrac{	ext{256}}{	ext{512}} = \dfrac{	ext{1}}{	ext{2}} = 1:2frequency of 2nd wavefrequency of 1st wave​=512256​=21​=1:2So pitch of first wave : pitch of second wave = 1 : 2.

Question 3

Question 3Two waves have the same pitch but their amplitudes are in the ratio of 1 : 2. Draw a figure to show the two waves.

Accepted Answer

In figure (a) the amplitude of wave A is 2 m and in figure (b) the amplitude of wave B is 4 m. But both the waves have same frequency (pitch).Ratio of amplitude of wave A to wave B = 2 : 4 = 1 : 2.

Question 4

Question 4Obtain relationship between the time period and frequency.

Accepted Answer

If T is the time period of a wave, then by definitionIn time T, the number of waves = 1∴ In 1 second, number of waves (or frequency) =f=1T	ext f = \dfrac{	ext{1}}{	ext{T}}f=T1​Thus,frequency=1Time period	ext{frequency} = \dfrac{	ext{1}}{	ext{Time period}}frequency=Time period1​ortime period=1frequency	ext{time period} = \dfrac{	ext{1}}{	ext{frequency}}time period=frequency1​

Question 5

Question 8If the amplitude of a wave is doubled, what will be the effect on its loudness?

Accepted Answer

The loudness (L) of a sound is directly proportional to the square of amplitude of wave.Loudness ∝ (amplitude)2L = (2)2 = 4 times.So, if the amplitude (a) of a wave is doubled, loudness will be four times.

Question 6

Question 9Name the unit in which the loudness of sound is expressed.

Accepted Answer

The unit in which loudness of sound is expressed is decibel (dB).

Question 7

Question 10Why is the loudness of sound heard by a plucked wire increased when mounted on a sound board?

Accepted Answer

Larger the surface area of the vibrating body, louder is the sound heard as a large vibrating area sends forth a greater amount of energy. By mounting a wire on a sound board, the surface area increases which in turn increases the loudness of the sound produced.

Question 8

Question 11State three factors on which loudness of sound heard by a listener depends.

Accepted Answer

The three factors on which loudness of sound heard by a listener depends are:Amplitude of wave.Distance of source of the sound.Surface area of the vibrating body.

Question 9

Question 12What determines the pitch of a sound?

Accepted Answer

Frequency determines the pitch of a sound. Higher the frequency, higher is the pitch and sound produced is shrill. Lower the frequency, lower is the pitch and sound produced is flat.

Question 10

Question 13Name the characteristic of sound related to its frequency.

Accepted Answer

The characteristic of sound related to its frequency is pitch.

Question 11

Question 14Which characteristic of sound makes it possible to recognize a person by his voice without seeing him?

Accepted Answer

Timbre or quality of sound makes it possible to recognize a person by his voice without seeing him. The vibrations produced by the vocal cord of each person have a characteristic wave form which is different for different persons.

Question 12

Question 15State the factors that determine(a) the pitch of a note.(b) the loudness of the sound heard.(c) the quality of the note.

Accepted Answer

(a) Frequency determines the pitch of a note.(b) Amplitude determines the loudness of the sound heard.(c) Wave form determines the quality of the note.

Question 13

Question 16Name the characteristic of the sound affected due to a change in its:(a) amplitude(b) wave form(c) frequency

Accepted Answer

(a) Loudness.(b) Quality.(c) Pitch.

Question 14

Question 17How is the pitch of a sound in a guitar changed if:(a) a thin wire is used(b) a wire under less tension is used?

Accepted Answer

(a) Pitch of sound will be higher if a thin wire is used in a guitar.Thin wires in stringed musical instruments produce sound with higher frequency and hence higher pitch.(b) Pitch of sound will be low if a wire under less tension is used in guitar.In stringed musical instruments, wires under less tension produce sound with lower frequency and hence lower pitch.

Question 15

Question 5Two musical notes of the same pitch and same loudness are played on two different instruments. Their wave patterns are as shown in figure.How do they differ in:(a) Loudness(b) Pitch and(c) Quality?

Accepted Answer

(a) Loudness will be same for both the instruments because they have same amplitude.(b) Pitch will be same for both the instruments as they have same frequencies.(c) Quality will be different as they have different wave forms as seen in the diagram of the given wave patterns.

Question 16

Question 6Figure shows four waves A, B, C and D.Name the wave which shows(a) a note from a musical instrument,(b) a soft note,(c) a shrill note.

Accepted Answer

(a) Note from a musical instrument is shown by figure (d) because the sound produced by the musical instruments comprises of different frequencies and amplitudes resulting in a mixed type of wave form.(b) Soft note is shown by figure (a) because this wave has low amplitude.(c) Shrill note is shown by figure (c) because this wave has high frequency.

Question 17

Question 7What happens when a lighted candle is placed in front of a loudspeaker making a loud and steady noise. Give reason.

Accepted Answer

When a lighted candle is placed in front of a loudspeaker producing a loud and steady noise, the flame of the candle flickers.A loudspeaker produces sound waves, which are longitudinal pressure waves in the air. These waves consist of alternating regions of compression and rarefaction that move outward from the speaker, causing the air near the loudspeaker to vibrate rapidly back and forth. The resulting air currents disturb the flame, making it flicker in step with the pressure variations of the sound waves.

Sound

Exercise 7 Numericals

Exercise 7 Short Answer Type Questions

Exercise 7 Think And Answer