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THEME ASSIGNMENT, , 1. OBJECTIVE TYPE QUESTIONS, , , , A. (i) bass (ii) pitch (iii) Decibel, , B. (i) True (ii) False (iii) False, , Cc. (i) (b) (ii) (©) (iii) (©), (iv) (a) (vd (c), , D. (i) The characteristic which distingushes a shrill sound from a bass, sound is called pitch of sound., (ii) The loudness of a sound wave is directly related to the energy, it carries., (iii) The loudness of sound is considered just audible if it is between, 10 dB to 25 dB., 2. Refer to Answer 1 (a), (b) and (c) of Exercise., 3. We hear a variety of sounds produced by different vibrating objects., We can easily make out the difference between the sound of sitar, and that of a violin. What makes these sounds different. The different, objects produce different sounds because either they have different, loudness or different pitch or both., 4. (a) Pitch depends upon the frequency of a vibrating body, i.e., the, higher the pitch, the more is the frequency and the lower the, , , , pitch, the less is the frequency., (b) Musical instruments like Jal Turang and flute are based on the, vibrations of air columns of different lengths, The siren also works on the same principle. When initially the, e siren is started, it produces sound of low pitch. However, as, the speed of its rotating discs increases, it produces a sound of, high pitch, 5. (a) Refer to Answer 5 (a) of Exercise., (b) Refer to Answer 5 (b) of Exercise., , o00, 8. ELECTRICITY, , OBJECTIVE TYPE QUESTIONS, A. 1. positive 2. repel, attract 3. free, 4. bound 5. protons, et

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ee, , Pa), , , , (b, , From a point, ultrasonic vibrations are sent. These vibrations,, after striking the sea bed, get reflected upward and are picked up., The time in which reflected sound is received is recorded., Knowing the speed of sound in water (1500 m/s) and the time, taken for the reflected sound to reach the sonar, the depth can, be calculated as illustrated by the example given below, , @ Let us suppose that it takes 2.4 s to receive the reflected sound,, It is clear that for 1.2 s the sound must have travelled downward, and for another 1,2 s it must have travelled upward. Now,, , ‘ Distance covered by sound, Speed of sound in water 2, , , , Time, m Distance covered by sound, 1500 - =< ts, |, Dastance covered by sound 1500 * 1.2 = 1800 m, Depth of sea 1800 m., , 9.(a) Loudness of sound : Loudness is the characteristic of a sound, which distinguishes a feeble sound from a loud sound of the, same frequency, , (b, , (i) Loudness depends on the area of vibrating body, (ii) Loudness decreases with the increase in distance from the, source of sound., 10.(a) Pitch : Pitch is the effect produced on the ear by the sound of, some particular frequency, A shrill sound is called high pitch sound, whereas a soft or, less shrill sound is called low pitch sound., (b), , , , Pitch depends upon the frequency of a vibrating, higher the pitch, the more is the frequency and the lower the, pitch, the less is the frequency, , body, ic., the, , 11. The property due to which two notes of same pitch and loudness, produced by two different vibrating bodies can be distinguished, is, called quality of sound., , This quality of sound is due to the formation of other notes which are, produced due to the vibration of various parts of musical instruments, and their sh; , therefore,, every note produced by the musical instrument has a definite, waveform, which in tums imparts it a special quality, , pes, Thus, as no pure note reaches the, , , , >

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ES er er ee, , , , , , Source of Loudness Effect of sound, sound level | on human ear, Whispering | 10dB—25dB | Just audible, Radio or | 30dB—40dB | Quite audible, T.V. at low comfortable sound, volume | |, Conversation 50dB-—60dB | Moderately loud, | | sound, * Light-vehicles | 60dB-70dB | Very loud sound, Mixer-cum- | 70dB-80dB | Very loud but, grinder/busy tolerable sound, crossing | |, Motor-cycle | 90dB—105dB | Noise very loud, heavy vehicle | [and uncomfortable _|, Lightning 120 dB — 130 dB | Very uncomfortable, , loud sound, , [150 dB and above | Painful sound, , , , , , , , ‘[Jet acroplane, , , , , , 6.(a) Laws of Reflection, , (i) Reflection of sound takes place only from hard and polished, surfaces in which incident wave, reflected wave and normal, lic in the same plane., , ic of, , , , (ii) The angle of incidence is always equal to the a, reflection., , (b) Mirrors, metals and stones reflect sound, (c) Curtains, gunny bags and straw absorb sound., , 7. (a) The repetition of the sound, which is reflected from a high, building or any such object is called an echo., (b) Ithas been found that an echo can be heard only, if':, © There is a high-rise building or hill., © Minimum distance between source of sound and reflecting, body is 17 m., , © The loudness of the sound should be sufficient so that it, can be heard afier reflection,, 8. (a) A device fitted in a ship to find the depth of sea is called sonar., It is based on the principle of reflection of sound., , , , a>

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Ea eed, , fi), , , , STUDY QUESTIONS, © 1. (a) Amplitude ; The maximum displacement of a vibrating body, from its mean position is called amplitude, , , , , , (b) _- Frequeney : The number of vibrations produced by a vibrating, body in one second is called frequency. It is denoted by, letter /, , {e) Time Period : The time in which a vibrating body completes, , one vibration is called time period. It is denoted by letter T, 2. If*f is the frequency of vibrating body and ‘T’ is the time period,, then, {vibrations are completed in Is, 1, one vibration is completed in Fs, But time taken to complete one vibration is its time period (7)., 1, , Frequency, , 1, T = Fe., Timperiod, , (a) Infrasonic waves (b) Sonic waves ({c) Ultrasonic waves, Human ear can hear sound waves in the range of sonic waves ie.,, between 20 Hz and 20,000 Hz only. Thus, human ear cannot hear, infrasonic or ultrasonic sound waves., , 4. Dogs, bats and dolphines use ultrasonic waves. —_ Bats can produce, vibration in the frequency range of 50 Hz to 80,000 Hz. Bats have, very weak eyes. When bats fly at night they produce ultrasonic, vibrations which cannot be heard by humans or the insects. When, these vibrations strike the insects they are reflected back. On receiving, the reflected sound the bat can locate the insect and cat it, , wo, , . (a) Monotone : Ifthe pitch, volume, rhythm and timbre of a voice, never fluctuate then it is said monotone. It will risk of losing, the audience as a result of this speech., , Thus, we can say, monotone is a sound which is repeated on, , one note without change of pitch while a pure note is a sound, , of one particular frequency, , The loudness of sound is measured inlecibels (dB), It signifies the, sound pressure level, Human ears can pick up sound from 10 dB to, 180 dB. The table given below, gives the loudness of various, sounds in decibels and their effect on human ear, , (b

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Ea: eer er ee, , , , 3. (a) Refer to Answer 2 of Exercise., (b) (i) Gaps are left in between rails, while laying a railway tine., , (ii) Electric transmission and telephone wires are kept slightly, loose when laid in summer., , (iii) Conerete floor is made in small slabs, rather than a single block, (iv) Iron bridges are mounted on steel rollers., , 4. (a) Plates of two different metals which are riveted together at a, number of points in such a way that they cannot slide on being, heated or cooled form a bimetallic strip, , (b) Refer to Answer 6 of Exercise:, 5. (a) Refer to Answer 7 (f) of Exercise., , (b) Refer to Answer 7 (g) of Exercise., , , , goa, 7. SOUND, °, OBJECTIVE TYPE QUESTIONS, A. 1. sonar 2. reflecting ultrasonic, 4. frequency 5. amplitude, , B. 1. The time taken by a vibrating body to complete one vibration is, called time period., , w, , . In order to produce an echo, the minimum distance between the, of sound and the reflecting body should be 17 m,, , , , , , The characteristic of sound which distinguishes between the shrill, sound and bass sound is called pitch., , 4. Shriller the sound more is the frequency of body, , on whistles are used to train dogs., , , , 2. False 3. True 4. False 5. False, 2. (d) 3. (b) 4. (c) 5. (a), 2.(d) 3. (b) 4. (c) 5. (a), , , , aD