{"id":4147,"date":"2016-05-06T11:49:00","date_gmt":"2016-05-06T11:49:00","guid":{"rendered":"http:\/\/mycbseguide.com\/blog\/ncert-solutions-class-9-science-sound-part-2\/"},"modified":"2018-06-07T15:52:16","modified_gmt":"2018-06-07T10:22:16","slug":"ncert-solutions-for-class-9-science-sound-part-2","status":"publish","type":"post","link":"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/","title":{"rendered":"NCERT Solutions for Class 9 Science Sound part 2"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_76 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 eztoc-toggle-hide-by-default' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#NCERT_Class_9_Science_Chapter_wise_Solutions\" >NCERT Class 9 Science Chapter wise Solutions<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#NCERT_Solutions_for_Class_9_Science_Sound_part_2\" >NCERT Solutions for Class 9 Science Sound part 2<\/a><ul class='ez-toc-list-level-6' ><li class='ez-toc-heading-level-6'><ul class='ez-toc-list-level-6' ><li class='ez-toc-heading-level-6'><ul class='ez-toc-list-level-6' ><li class='ez-toc-heading-level-6'><ul class='ez-toc-list-level-6' ><li class='ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#1_What_is_sound_and_how_is_it_produced\" >1. What is sound and how is it produced?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#2_Describe_with_the_help_of_a_diagram_how_compressions_and_rarefactions_are_produced_in_air_near_a_source_of_sound\" >2. Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#3_Cite_an_experiment_to_show_that_sound_needs_a_material_medium_for_its_propagation\" >3. Cite an experiment to show that sound needs a material medium for its propagation.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#4_Why_is_sound_wave_called_a_longitudinal_wave\" >4. Why is sound wave called a longitudinal wave?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#5_Which_characteristic_of_the_sound_helps_you_to_identify_your_friend_by_his_voice_while_sitting_with_others_in_a_dark_room\" >5. Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#6_Flash_and_thunder_are_produced_simultaneously_But_thunder_is_heard_a_few_seconds_after_the_flash_is_seen_why\" >6. Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#7_A_person_has_a_hearing_range_from_20_Hz_to_20_kHz_What_are_the_typical_wavelengths_of_sound_waves_in_air_corresponding_to_these_two_frequencies_Take_the_speed_of_sound_in_air_as\" >7. A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#8_Two_children_are_at_opposite_ends_of_an_aluminium_rod_One_strikes_the_end_of_the_rod_with_a_stone_Find_the_ratio_of_times_taken_by_the_sound_wave_in_air_and_in_aluminium_to_reach_the_second_child\" >8. Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#9_The_frequency_of_a_source_of_sound_is_100_Hz_How_many_times_does_it_vibrate_in_a_minute\" >9. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#10_Does_sound_follow_the_same_laws_of_reflection_as_light_does_Explain\" >10. Does sound follow the same laws of reflection as light does? Explain.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#11_When_a_sound_is_reflected_from_a_distant_object_an_echo_is_produced_Let_the_distance_between_the_reflecting_surface_and_the_source_of_sound_production_remains_the_same_Do_you_hear_echo_sound_on_a_hotter_day\" >11. When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#13_A_stone_is_dropped_from_the_top_of_a_tower_500_m_high_into_a_pond_of_water_at_the_base_of_the_tower_When_is_the_splash_heard_at_the_top_Given_and_speed_of_sound\" >13. A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, and speed of sound =.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#14_A_sound_waves_travels_at_a_speed_of_If_its_wavelength_is_15_cm_what_is_the_frequency_of_the_wave_Will_it_be_audible\" >14. A sound waves travels at a speed of. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-16\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#15_What_is_reverberation_How_can_it_be_reduced\" >15. What is reverberation? How can it be reduced?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-17\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#16_What_is_loudness_of_sound_What_factors_does_it_depend_on\" >16. What is loudness of sound? What factors does it depend on?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-18\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#17_Explain_how_bats_use_ultrasound_to_catch_a_prey\" >17. Explain how bats use ultrasound to catch a prey.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-19\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#18_How_is_ultrasound_used_for_cleaning\" >18. How is ultrasound used for cleaning?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-20\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#19_Explain_the_working_and_application_of_a_sonar\" >19. Explain the working and application of a sonar.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-21\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#20_A_sonar_device_on_a_submarine_sends_out_a_signal_and_receives_an_echo_5_s_later_Calculate_the_speed_of_sound_in_water_if_the_distance_of_the_object_from_the_submarine_is_3625_m\" >20. A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-22\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#21_Explain_how_defects_in_a_metal_block_can_be_detected_using_ultrasound\" >21. Explain how defects in a metal block can be detected using ultrasound.<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-6'><a class=\"ez-toc-link ez-toc-heading-23\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#22_Explain_how_the_human_ear_works\" >22. Explain how the human ear works.<\/a><\/li><\/ul><\/li><\/ul><\/li><\/ul><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-24\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#NCERT_Solutions_for_Class_9_Science\" >NCERT Solutions for Class 9 Science<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-25\" href=\"https:\/\/mycbseguide.com\/blog\/ncert-solutions-for-class-9-science-sound-part-2\/#CBSE_app_for_Class_9\" >CBSE app for Class 9<\/a><\/li><\/ul><\/nav><\/div>\n<p>NCERT Solutions for Class 9 Science Sound part 2 Class 9 Science book solutions are available in PDF format for free download. These ncert book chapter wise questions and answers are very helpful for CBSE exam. CBSE recommends NCERT books and most of the questions in CBSE exam are asked from NCERT text books. Class 9 Science chapter wise NCERT solution for Science Book for all the chapters can be downloaded from our website and myCBSEguide mobile app for free.<\/p>\n<p style=\"text-align: center;\"><strong>NCERT solutions for Science\u00a0Sound <a class=\"button\" href=\"https:\/\/mycbseguide.com\/downloads\/cbse-class-09-science\/1218\/ncert-solutions\/5\/\">Download as PDF<\/a><\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter\" src=\"https:\/\/media-mycbseguide.s3.ap-south-1.amazonaws.com\/images\/blog\/09_Science_Book.jpg\" alt=\"NCERT Solutions for Class 9 Science Sound part 2\" width=\"172\" height=\"231\" \/><\/p>\n<h2><span class=\"ez-toc-section\" id=\"NCERT_Class_9_Science_Chapter_wise_Solutions\"><\/span><span class=\"underline-text\">NCERT Class 9 Science Chapter wise Solutions<\/span><span class=\"ez-toc-section-end\"><\/span><\/h2>\n<ul>\n<li>01 \u2013 \u00a0Matter in Our Surroundings<\/li>\n<li>02 \u2013 Is Mattter Around us Pure<\/li>\n<li>03 \u2013 Atoms and Molecules<\/li>\n<li>04 \u2013 Structure of the Atom<\/li>\n<li>05 \u2013 The Fundamental Unit of Life<\/li>\n<li>06 \u2013 Tissues<\/li>\n<li>07 \u2013 Diversity in Living Organisms<\/li>\n<li>08 \u2013 Motion<\/li>\n<li>09 \u2013 Force and Laws of Motion<\/li>\n<li>10 \u2013 Gravitation<\/li>\n<li>11 \u2013 Word and Energy<\/li>\n<li>12 \u2013 Sound<\/li>\n<li>13 \u2013 Why Do We Fall Ill<\/li>\n<li>14 \u2013 Natural Resources<\/li>\n<li>15 \u2013 Improvement in Food Resources<\/li>\n<\/ul>\n<h2><span class=\"ez-toc-section\" id=\"NCERT_Solutions_for_Class_9_Science_Sound_part_2\"><\/span>NCERT Solutions for Class 9 Science Sound part 2<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"1_What_is_sound_and_how_is_it_produced\"><\/span><strong>1. What is sound and how is it produced?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Sound is a form of energy that produces a sensation of hearing in our ears.<\/p>\n<p style=\"text-align: justify;\">Sound gets produced when any object vibrates\/oscillates.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"2_Describe_with_the_help_of_a_diagram_how_compressions_and_rarefactions_are_produced_in_air_near_a_source_of_sound\"><\/span><strong>2. Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans.<\/strong><\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" id=\"Picture 25\" class=\"\" style=\"height: 140px; width: 383px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image015.png\" \/><\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"3_Cite_an_experiment_to_show_that_sound_needs_a_material_medium_for_its_propagation\"><\/span><strong>3. Cite an experiment to show that sound needs a material medium for its propagation.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Take an electric bell and an airtight glass bell jar. The electric bell is suspended inside the airtight bell jar. The bell jar is connected to a vacuum pump If you press the switch you will be able to hear the bell. Now start the vacuum pump. When the air in the jar is pumped out gradually, the sound becomes fainter, although the same current is passing through the bell.<\/p>\n<p style=\"text-align: justify;\">After some time when less air is left inside the bell jar you will hear a very feeble sound. Now if we evacuate the bell jar no sound is heard.<\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" id=\"Picture 7\" class=\"\" style=\"height: 146px; width: 190px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image016.jpg\" alt=\"Chapter_12_Sound_Science_CBSE_Class_9th_Q3.jpg\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>Result:<\/strong> The above mentioned activity shows that sound needs a medium to propagate.<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"4_Why_is_sound_wave_called_a_longitudinal_wave\"><\/span><strong>4. Why is sound wave called a longitudinal wave?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Sound wave is called a longitudinal wave because sound waves travel in the air through compressions and rarefactions.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"5_Which_characteristic_of_the_sound_helps_you_to_identify_your_friend_by_his_voice_while_sitting_with_others_in_a_dark_room\"><\/span><strong>5. Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Pitch of the sound wave.<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"6_Flash_and_thunder_are_produced_simultaneously_But_thunder_is_heard_a_few_seconds_after_the_flash_is_seen_why\"><\/span><strong>6. Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Since speed of thunder (sound) is much less (332 m\/s) as compared to speed of flash (light) which is about <img decoding=\"async\" style=\"height: 22px; width: 74px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image017.png\" \/>therefore light travels faster than sound hence thunder is heard a few seconds after the flash is seen.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"7_A_person_has_a_hearing_range_from_20_Hz_to_20_kHz_What_are_the_typical_wavelengths_of_sound_waves_in_air_corresponding_to_these_two_frequencies_Take_the_speed_of_sound_in_air_as\"><\/span><strong>7. A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as<img decoding=\"async\" style=\"height: 22px; width: 68px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image018.png\" \/>.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>For 20 Hz sound waves the wavelength would be<\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" style=\"height: 19px; width: 68px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image004.png\" \/><\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" style=\"height: 19px; width: 11px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image019.png\" \/> = v\/n = 344\/20 = 17.2 m<\/p>\n<p style=\"text-align: justify;\">For 20 kHz sound waves the wavelength would be<\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" style=\"height: 19px; width: 68px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image004.png\" \/><\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" style=\"height: 22px; width: 140px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image020.png\" \/>\/20000 Hz = 0.0172 m<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"8_Two_children_are_at_opposite_ends_of_an_aluminium_rod_One_strikes_the_end_of_the_rod_with_a_stone_Find_the_ratio_of_times_taken_by_the_sound_wave_in_air_and_in_aluminium_to_reach_the_second_child\"><\/span><strong>8. Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Since speed of sound in air = 344 m\/s<\/p>\n<p style=\"text-align: justify;\">and speed of sound in aluminium = 6420 m\/s<\/p>\n<p style=\"text-align: justify;\">we know that v = distance\/time therefore time = d\/v<\/p>\n<p style=\"text-align: justify;\">time taken by sound wave in air\/time taken by sound wave in aluminium<\/p>\n<p style=\"text-align: justify;\">= d\/344: d\/6420 = 6420\/344 = 18.66\/1<\/p>\n<p style=\"text-align: justify;\">the sound will take 18.66 times more time through air than in aluminium in reaching other boy.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"9_The_frequency_of_a_source_of_sound_is_100_Hz_How_many_times_does_it_vibrate_in_a_minute\"><\/span><strong>9. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Frequency of source of sound being 100 Hz means the sound source vibrates 100 times in one second.<\/p>\n<p style=\"text-align: justify;\">therefore vibrations made by sound source in 1 min (60 sec) = <img decoding=\"async\" style=\"height: 19px; width: 56px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image021.png\" \/>= 6000<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"10_Does_sound_follow_the_same_laws_of_reflection_as_light_does_Explain\"><\/span><strong>10. Does sound follow the same laws of reflection as light does? Explain.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Yes. Sound follows the same laws of reflection as light does. We can say that because here the directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane.<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"11_When_a_sound_is_reflected_from_a_distant_object_an_echo_is_produced_Let_the_distance_between_the_reflecting_surface_and_the_source_of_sound_production_remains_the_same_Do_you_hear_echo_sound_on_a_hotter_day\"><\/span><strong>11. When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>As the sensation of sound persists in our brain for about 0.1 s.To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s. There for the total distance covered by the sound from the point of generation to the reflecting surface and back should be at least <img decoding=\"async\" style=\"height: 26px; width: 130px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image022.png\" \/>= 34.4 m. Thus, for hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be half of this distance, that is, 17.2 m. Speed of sound will increase with increase in temperature. Therefore, on a hotter day speed of sound will be greater hence echoes may be heard more than once because of multiple reflections of sound result will be no distinct echo will be heard by us.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<p style=\"text-align: justify;\"><strong>12. Give two practical applications of reflection of sound waves.<\/strong><\/p>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Two practical applications of reflection of sound waves<\/p>\n<p style=\"text-align: justify;\"><strong>i.<\/strong> Megaphones or loudhailers, horns, musical instruments such as trumpets and <em>shehanais<\/em>, are all designed to send sound in a particular direction without spreading it in all directions.<\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" id=\"Picture 17\" class=\"\" style=\"height: 83px; width: 310px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image023.png\" \/><\/p>\n<p style=\"text-align: justify;\"><strong>ii.<\/strong> Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs. In stethoscopes the sound of the patient\u2019s heartbeat reaches the doctor\u2019s ears by multiple reflection of sound.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"13_A_stone_is_dropped_from_the_top_of_a_tower_500_m_high_into_a_pond_of_water_at_the_base_of_the_tower_When_is_the_splash_heard_at_the_top_Given_and_speed_of_sound\"><\/span><strong>13. A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, <img decoding=\"async\" style=\"height: 24px; width: 91px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image024.png\" \/>and speed of sound =<img decoding=\"async\" style=\"height: 22px; width: 68px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image025.png\" \/>.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <img decoding=\"async\" style=\"height: 24px; width: 100px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image026.png\" \/><\/strong><\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" style=\"height: 19px; width: 125px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image027.png\" \/>= 10000<\/p>\n<p style=\"text-align: justify;\">v = <img decoding=\"async\" style=\"height: 21px; width: 55px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image028.png\" \/> = 100 m\/s<\/p>\n<p style=\"text-align: justify;\">we also know that v = u + gt = 0 + 10t<\/p>\n<p style=\"text-align: justify;\">100 = 10t or, Time taken by stone to reach the pond surface (t) = 100\/10 = 10 sec<\/p>\n<p style=\"text-align: justify;\">therefore, time taken by sound to reach the top from pond surface = d\/v = 500\/340<\/p>\n<p style=\"text-align: justify;\">= 1.47 sec<\/p>\n<p style=\"text-align: justify;\">so the total time taken for splash being heard at the top = 10 + 1.47 = 11.47 s<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"14_A_sound_waves_travels_at_a_speed_of_If_its_wavelength_is_15_cm_what_is_the_frequency_of_the_wave_Will_it_be_audible\"><\/span><strong>14. A sound waves travels at a speed of<img decoding=\"async\" style=\"height: 22px; width: 68px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image029.png\" \/>. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Since we know that<img decoding=\"async\" style=\"height: 19px; width: 57px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image030.png\" \/><\/p>\n<p style=\"text-align: justify;\">339 = 0.015 <img decoding=\"async\" style=\"height: 14px; width: 37px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image031.png\" \/><\/p>\n<p style=\"text-align: justify;\">\u03bd = 339\/0.015 = 22600 Hz<\/p>\n<p style=\"text-align: justify;\">Since the resulting frequency is beyond the audible range of human beings (20Hz to 20kHz) therefore sound will not be audible to human ears.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"15_What_is_reverberation_How_can_it_be_reduced\"><\/span><strong>15. What is reverberation? How can it be reduced?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>The repeated reflection of sound due to which sound persists for a long time is called reverberation.<\/p>\n<p style=\"text-align: justify;\">To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fibreboard, rough plaster or draperies. The seat materials are also selected on the basis of their sound absorbing properties.<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"16_What_is_loudness_of_sound_What_factors_does_it_depend_on\"><\/span><strong>16. What is loudness of sound? What factors does it depend on?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Loudness is a measure of the response of the ear to the sound. Even when two sounds are of equal intensity, we may hear one as louder than the other simply because our ear detects it better.<\/p>\n<p style=\"text-align: justify;\">Loudness of sound depends upon the amplitude of those sound waves. Higher is the amplitude of vibrating air particles louder will be the sound.<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"17_Explain_how_bats_use_ultrasound_to_catch_a_prey\"><\/span><strong>17. Explain how bats use ultrasound to catch a prey.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Bats search out prey and fly in dark night by emitting and detecting reflections of ultrasonic waves. The high-pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to bat\u2019s ear. The nature of reflections tells the bat where the obstacle or prey is and what it is like.<\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" id=\"Picture 10\" style=\"height: 233px; width: 377px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image032.png\" alt=\"Ultrasound_Bat_Chapter_12_Sound_Science_CBSE_Class_9th.jpg\" \/><\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"18_How_is_ultrasound_used_for_cleaning\"><\/span><strong>18. How is ultrasound used for cleaning?<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Ultrasound is generally used to clean parts located in hard-to-reach places, for example, spiral tube, odd shaped parts, electronic components etc. Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution. Due to the high frequency, the particles of dust, grease and dirt get detached and drop out. The objects thus get thoroughly cleaned.<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"19_Explain_the_working_and_application_of_a_sonar\"><\/span><strong>19. Explain the working and application of a sonar.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.<\/p>\n<p style=\"text-align: justify;\">Sonar consists of a transmitter and a detector and is installed in a boat or a ship. The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. Let the time interval between transmission and reception of ultrasound signal be <em>t <\/em>and the speed of sound through seawater be <em>v<\/em>. The total distance, 2<em>d <\/em>travelled by the ultrasound is then, 2<em>d<img decoding=\"async\" style=\"height: 16px; width: 43px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image033.png\" \/><\/em>.<\/p>\n<p style=\"text-align: justify;\">The above method is called echo-ranging. The sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarine, icebergs, sunken ship etc.<\/p>\n<p style=\"text-align: justify;\"><img decoding=\"async\" id=\"Picture 4\" class=\"\" style=\"height: 125px; width: 231px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image034.png\" alt=\"400px-Sonar_Principle_EN.svg.png\" \/><\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"20_A_sonar_device_on_a_submarine_sends_out_a_signal_and_receives_an_echo_5_s_later_Calculate_the_speed_of_sound_in_water_if_the_distance_of_the_object_from_the_submarine_is_3625_m\"><\/span><strong>20. A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Distance of object from submarine = 3625 m<\/p>\n<p style=\"text-align: justify;\">therefore, distance travelled by sonar waves <img decoding=\"async\" style=\"height: 19px; width: 74px;\" src=\"https:\/\/media-mycbseguide.s3.amazonaws.com\/images\/static\/ncert\/09\/science\/ch12\/image035.png\" \/>= 7250 m<\/p>\n<p style=\"text-align: justify;\">since, speed = distance\/time= 7250\/5 = 1450 m\/s<\/p>\n<hr \/>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"21_Explain_how_defects_in_a_metal_block_can_be_detected_using_ultrasound\"><\/span><strong>21. Explain how defects in a metal block can be detected using ultrasound.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>Ultrasounds can be used to detect cracks and flaws in metal blocks. Metallic components are generally used in construction of big structures like buildings, bridges, machines and also scientific equipment. The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure. Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect<\/p>\n<hr \/>\n<p style=\"text-align: center;\">NCERT Solutions for Class 9 Science Sound part 2<\/p>\n<h6 style=\"text-align: justify;\"><span class=\"ez-toc-section\" id=\"22_Explain_how_the_human_ear_works\"><\/span><strong>22. Explain how the human ear works.<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h6>\n<p style=\"text-align: justify;\"><strong>Ans. <\/strong>The outer ear is called \u2018pinna\u2019. It collects the sound from the surroundings. The collected sound passes through the auditory canal. At the end of the auditory canal there is a thin membrane called the ear drum or tympanic membrane. When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones (the hammer, anvil and stirrup) in the middle ear. The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"NCERT_Solutions_for_Class_9_Science\"><\/span>NCERT Solutions for Class 9 Science<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>NCERT Solutions Class 9 Science PDF (Download) Free from myCBSEguide app and myCBSEguide website. Ncert solution class 9 Science includes text book solutions .NCERT Solutions for CBSE Class 9 Science have total 15 chapters. 9 Science NCERT Solutions in PDF for free Download on our website. Ncert Science class 9 solutions PDF and Science ncert class 9 PDF solutions with latest modifications and as per the latest CBSE syllabus are only available in myCBSEguide.<\/p>\n<h2><span class=\"ez-toc-section\" id=\"CBSE_app_for_Class_9\"><\/span>CBSE app for Class 9<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>To download\u00a0NCERT Solutions for class 9 Science, Computer Science, Home Science,Hindi ,English, Maths Social Science do check myCBSEguide app or website. myCBSEguide provides sample papers with solution, test papers for chapter-wise practice, NCERT solutions, NCERT Exemplar solutions, quick revision notes for ready reference, CBSE guess papers and CBSE important question papers. Sample Paper all are made available through\u00a0<a href=\"https:\/\/play.google.com\/store\/apps\/details?id=in.techchefs.MyCBSEGuide&amp;referrer=utm_source%3Dmycbse_bottom%26utm_medium%3Dtext%26utm_campaign%3Dmycbseads\"><strong>the best app for CBSE students<\/strong><\/a>\u00a0and myCBSEguide website.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>NCERT Solutions for Class 9 Science Sound part 2 Class 9 Science book solutions are available in PDF format for free download. These ncert book chapter wise questions and answers are very helpful for CBSE exam. CBSE recommends NCERT books and most of the questions in CBSE exam are asked from NCERT text books. 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