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ICSE Class 8 Notes 2024 : Environmental Science

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Grade 7 Physics Class Test I. Fill in the blanks. 1. The speed of sound in air in normal conditions is _____________________. 2. Speed of sound in air depends on the __________________________ and ____________________________ in air. 3. Speed of sound is least in ________________________ media. 4. Speed of sound in gas depends on its ____________________ . 5. Speed of sound in water is ____________________. 6. An object travelling with a speed greater than the speed of sound is said to be having _________________________speed. 7. Metallic sheets, plane polished smooth walls are ____________________reflectors of sound. 8. Sound cannot travel through ____________________ media. 9. To hear a clear echo _____________________ should be the distance between the source of sound and the reflecting surface. 10. SONAR stands for ____________________________________________. 11. Megaphones work on the principles of ___________________________ of sound. 12. The three characteristics of sound are _________________________, ____________________________ and _____________________________. 13. Loudness mainly depends on ______________________ of vibration.The maximum displacement of a vibrating particle from its mean position on either side is _________________________. 14. The time taken by a particle to complete one vibration is the ________________________. 15. The no. of vibrations completed by a medium particle in unit time is known as its _________________________. 16. The S.I unit of frequency is ______________________. 17. Pitch determines the ______________________ of a sound. 18. Sounds of same pitch and loudness but produced by two different sources can be distinguished by the ____________________ of sound. 19. A normal human ear can hear clear sounds with frequencies ranging from ___________________________ to __________________ only. 20. Sounds having frequencies lower than 20 Hz are known as _______________________. 21. SONAR uses ______________________ sound waves for finding objects under water. -222. Bats can produce and hear ___________________ sounds. 23. A sound which produces a jarring effect in our ears is called a ______________________. 24. The loudness of sound is measured on the ____________________ scale. 25. A normal person can tolerate sound of loudness level upto ____________. 26. Noise pollution is caused due to sounds above ____________ dB. 27. Sounds of ________dB or more can cause heart attack and sometimes even death. 28. The vibrations are carried to the brain through ___________________ nerve in the form of signals. 29. Sound is the form of energy that causes sensation of hearing in our ______________. 30. During earthquakes and volcanic eruptions, _______________________ sounds are produced. II. 1. 2. 3. 4. 5. 6. Give reasons for the following. Speed of sound is maximum in hydrogen gas. Speed of sound is much less than the speed of light. Echo, t = 2d/t Curtains are bad reflectors of sound. SONAR is used to determine the depth of the sea. In large auditoriums, the walls, ceiling and floor are covered with heavy carpets. 7. Bats can easily fly in the night. 8. Sound waves travel faster in high temperature. 9. Speed of sound increases with increase in humidity. 10. Red Indians used the propagation of sound through solid during battles. *****************

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