Selina solutions concise physics class 8 icse Solutions for Chapter 7 sound

Q1) Write true or false for each statement :

(a) When sound propagates in air, it does not carry energy with it.

(b) In a longitudinal wave, compression and rarefaction are formed.

(c) The distance from one compression to the nearest rarefaction is called wavelength.

(d) The frequency is measured in seconds.

(e) The quality of a sound depends on the amplitude of wave.

(f) The pitch of sound depends on frequency.

(g) Decibel is the unit of a sound.

Q2) Fill in the blanks.

(a) The time period of a wave is 2 s. Its frequency is_______.

(b) The pitch of a stringed instrument is increased by _______ tension in the string.

(c) The pitch of a flute is decreased by _______ the length of the air column.

(d) Smaller the membrane,_______ is the pitch.

(e) If a drum is beaten hard, its loudness _______ .

(f) A tuning fork produces sound of _______ frequency.

Q3) Match the following :

Q4) Select the correct alternative

(a) Sound can not travel in

1. Solid

2. Liquid

3. Gas

4. Vacuum

(b) When sound travels in form of a wave

1. The particles of medium move from the source to the listener

2. The particles of medium remains stationary

3. The particles of medium start vibrating up and down

4. The particles of medium transfer energy without leaving their mean positions

(c) The safe limit of loudness of audible sound is

1. 0 to 89dB

2. Above 80dB

3. 120dB

4. Above 120 dB

(d) The unit of loudness is

1. Cm

2. Second

3. Hertz

4. Decibel

(e) In a piano, pitch is decreased by

1. Using thicker string

2. Increasing tension

3. Reducing length of string

4. Striking it hard

Q1) How does sound travel in air?

Q2) What is longitudinal wave?

Q3) Explain the mechanism of formation of a longitudinal wave when source vibrates in air.

Q4) Define the following terms:

(a) Amplitude

(b) Frequency

(c) Time period

Q5) Obtain relationship between the time period and frequency.

Q6) Name three characteristics of a musical sound.

Q7) Name the quantity from below which determines the loudness of a sound wave:

(a) Wavelength

(b) Frequency, and

(c) Amplitude

Q8) How is loudness related to the amplitude of wave?

Q9)If the amplitude of a wave is doubled, what will be the effect on its loudness?

Q10) How does the wave pattern of a loud note differ from a soft note? Draw a diagram.

Q11) Name the unit in which the loudness of sound is expressed?

Q12) Why is the loudness of sound heard by a plucked wire increased when mounted on a soundboard?

Q13) State three factors on which loudness of sound heard by a listener depends.

Q14) What determines the pitch of a sound?

Q15) Name the characteristics of sound related to its frequency.

Q16) Name and define the characteristic which enables one to distinguish two sounds of same loudness, but of different frequencies, given by the same instrument.

Q17) Draw a diagram to show the wave pattern of high pitch note and a low pitch note, but of the same loudness.

Q18) How is it possible to detect the filling of a bucket under a water tap by hearing the sound standing at a distance?

Q19) The frequencies of notes given by flute, guitar and trumpet are respectively 400 Hz, 200 Hz and 500 Hz. Which one of these has the highest pitch?

Q20) Figure shows two jars A and B containing water up to different heights. Which will produce sound of higher pitch when air is blown on them?

Q21) Two identical guitars are played by two persons to give notes of the same pitch. Will they differ in quality? Give reason for your answer.

Q22) Two 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

Q23) Which characteristics of sound makes it possible to recognize a person by his voice without seeing him?

Q24) State the factors that determine

(a) The pitch of a note

(b) The loudness of the sound heard

(c) the quality of the note.

Q25) Name the characteristics of the sound affected due to a change in its

(a) amplitude (b) waveform (c) frequency

Q26) Figure 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

Q27) How is the pitch of sound in a guitar changed if (a) thin wire is used, (b) wire under less tension is used?