Find the frequencies of the first three harmonics of a piano string of length 1.5m, if the velocity of the wave on the string is 120ms-1

Answer Details

The frequency of a wave on a string is related to its length, tension, and mass per unit length by the equation f= (1/2L) * sqrt(T/μ), where L is the length of the string, T is the tension in the string, μ is the mass per unit length, and f is the frequency of the wave. In this question, the length of the string is given as 1.5m and the velocity of the wave on the string is given as 120ms^-1. We need to first calculate the tension in the string. The velocity of a wave on a string is also related to tension and mass per unit length by the equation v= sqrt(T/μ), where v is the velocity of the wave. Rearranging this equation, we get T= μv^2. Substituting the given values, T= (1/120)^2= 6.94 N. Now we can use the equation for frequency to calculate the frequencies of the first three harmonics. The first harmonic has one antinode (at the middle of the string), the second harmonic has two antinodes (one at the middle and one at a quarter of the length of the string from one end), and the third harmonic has three antinodes (at the middle, a quarter, and three-quarters of the length of the string from one end). The formula for frequency for a string fixed at both ends is f= (n/2L) * v, where n is the harmonic number. Therefore, for the first three harmonics, we have: f1= (1/2*1.5) * 120= 40Hz f2= (2/2*1.5) * 120= 80Hz f3= (3/2*1.5) * 120= 120Hz Therefore, the correct option is 40Hz, 80Hz, 120Hz.