A wire of diameter `0.04 cm` and made of steel of density `8000 kg//m^(3)` is under a tension of `80 N`. A fixed length of `50 cm` is set into transverse vibrations . How would you cause vibrations of frequency `840 Hz` to predominate in intensity ?

Explanation

`n_(0) ("fundamental frequency") = (1)/( 2I) sqrt(T//m)`
Here `m = pi r^(2) rho = pi (0.02 xx 10^(-2))^(2) xx 8000`
` = 32 pi xx 10^(-5) kg//m`
` n = (1)/( 2 xx 0.5) sqrt ((80)/( 32 xx 10^(-5))) = 280 Hz`
Obviously `840 Hz` is its `3 rd` harmonic . The third harmonic needs a node `1//3` point. So strike the wire at `1//6` point and touch gently `1//3` point to make `840 Hz` dominant.