why are strings of different thicknesses and materials used in a sitar

1.	why are strings of different thicknesses and materials used in a sitar or a violin ?
Answer» SOLUTION :Fundamental frequency of streched string `v= 1/2L sqrt T/m`. when we use string of DEFFERENT thiknesses and materials, they have different values of MASS as PER unit length (m). So the strings will PRODUCED notes of different frequencies.

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