The fundamental frequency of string stretched with a weight of 4kg is 256 Hz. The weight required to produce its octave is _____?

24 kg wt

16 kg wt

12 kg wt

None of these

The frequency of a stretched string is proportional to the square root of the tension.

To produce an octave (double frequency), the tension must increase fourfold.

Since the original tension is from 4 kg, the required tension is

4 \times 4 = 16 kg wt .