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Threads of Curiosity A tone is a sound of a single frequency like that produced by a tuning fork or by oral whistling (Fig. 10.25a). A musical note like the sound produced by plucking a tanpura string or singing (Fig. 10.25b) is a combination of a lowest (a) frequency called the fundamental and higher frequencies called overtones, which together create a rich and pleasant sound. Indian string instruments like the sarangi, sitar, and veena oftenuseextrastringstoenrichthiscombination. (b) Even when different instruments like a flute, ektara, or tabla play the same note at the Fig. 10.25: Schematic representation same loudness each sounds unique. This quality of the sound produced by is called timbre, and comes from their shape, (a) a vibrating tuning fork or a person material and construction, which determine the whistling, and (b) a child singing pattern and intensity of the overtones. An octave is the interval between two notes where one has double the frequency of the other (for example, 200 Hz and 400 Hz), measured between their fundamental frequencies. Meet a Scientist Sir C. V. Raman won India’s first Nobel Prize in Science for discoveringtheRamanEffectinlight.Healsomadeimportant contributions to acoustics by studying Indian percussion instruments, such as the tabla and mridangam to understand how they produce rich and nuanced sounds. Threads of Curiosity Indian drums like the tabla (Fig. 10.26) or mridangam have a black patch at the centre of the drum head membrane called the syaahi. This patch alters the vibration of the membrane, allowing these instruments to produce a rich variety of sounds. The syaahi also gives a level of tonal control rarely found in other drums. Fig. 10.26: A tabla set 10.7 Reflection of Sound CuriositySound waves can bounce off obstacles like solids or liquids and this is Chapter 10known as the reflection of sound. Sound follow the same laws of reflection as those of light which you have learned earlier. The directions in which the sound is incident and is thereafter reflected make equal angles with the normal to the reflecting surface at the point of incidence, with all three lying in the same plane. One of the most common examples of the reflection of sound is an echo. 200 Exploration|Grade 9