\text { Show that } \frac{1}{f} \text { is given by: } Figure 6 shows apparatus used to determine the speed of sound in air. An air column is created in the upper part of a measuring cylinder by partly filling the cylinder with water. A loudspeaker connected to a signal generator is held above the air column.The frequency of the sound is gradually increased from zero until the sound suddenly becomes much louder. At this point, the frequency f of the first harmonic of the stationary wave is equal to the frequency of the signal from the signal generator.

I is measured with a metre ruler. \text { Figure } 7 \text { is a plot of } \frac{1}{f} \text { against } l \text {. }

fis recorded from the signal generator. The length / of the air column is varied by changing the volume of water in the measuring cylinder. fis measured for a range of values of 1.