Sound

This chapter explains how sound is produced, how it travels and how we hear it. Sound is produced by vibrating bodies: the stretched skin of a drum, the strings of a sitar, the air column in a flute and the vocal cords in our larynx. You will learn that sound needs a medium such as a solid, liquid or gas to travel and cannot pass through a vacuum, as the bell jar experiment shows. You will study how the human ear works, with the eardrum vibrating when sound reaches it and passing the vibrations to the inner ear and then to the brain. You will describe vibrations using amplitude, time period and frequency, measured in hertz (Hz). Loudness depends on amplitude, being proportional to its square, while pitch depends on frequency. Humans can hear sounds of frequencies from about 20 Hz to 20,000 Hz. The chapter also distinguishes music from noise, explains noise pollution, its harmful effects such as hearing loss, and measures to control it.

Detailed Worksheet: Sound Section A - Definitions (10 marks) 1. What is a vibration? Name the vibrating part that produces sound in (i) a tabla (ii) a flute. (2 marks) 2. Define amplitude and time period of a vibration. (2 marks) 3. Define frequency. What is its SI unit? (2 marks) 4. What are inaudible sounds? Name the two kinds of inaudible sounds based on frequency. (2 marks) 5. What is noise pollution? Name two sources of noise pollution. (2 marks) Section B - Calculations and Applications (15 marks) 6. A pendulum completes 40 oscillations in 10 seconds. Find its frequency and time period. (3 marks) 7. The time period of a vibrating object is 0.005 s. Find its frequency. Will a human being be able to hear the sound it produces? Give a reason. (3 marks) 8. A bat produces sound of frequency 50,000 Hz and an elephant produces a rumble of frequency 15 Hz. Can a human hear either? Find the time period of the bat's sound. (3 marks) 9. If the amplitude of a vibration is doubled, by what factor does the loudness increase? If the amplitude is made three times, what happens to the loudness? (3 marks) 10. Two sounds have frequencies of 256 Hz and 512 Hz and the same amplitude. Which has the higher pitch? Compare their time periods and state which one would sound shriller. (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of the human ear, showing the outer ear, ear canal, eardrum and inner ear. Explain briefly how we hear. (4 marks) 12. Draw a labelled diagram of the bell jar experiment and explain what it shows about the propagation of sound. (3 marks) 13. Draw two wave sketches showing (i) a sound of high amplitude and low frequency (ii) a sound of low amplitude and high frequency. Label amplitude on each. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain how the human voice is produced. Why do men, women and children have voices of different pitch? (5 marks) 15. On the Moon there is no atmosphere. Explain why astronauts on the Moon cannot hear each other directly and how they talk. Also explain why we can hear sounds through a wall or underwater. (5 marks) 16. Describe four harmful effects of noise pollution on health and suggest five measures to reduce noise pollution in a residential area near a busy road. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Show the formula and units in every numerical and label all diagrams neatly.