1) Why does the stroboscope appear to make the vibrations stop at certain frequencies? Why does it appear to be two strings at 240 Hz and three strings at 360 Hz?
2) If the frequency is variable and the length of the closed (at both ends) tube is fixed at 45 cm, sketch the plastic tube showing the positions of the nodes and anti-nodes for the three lowest resonant frequencies.
3) If the frequency is held constant at 1350 Hz and the length of the closed (at both ends) tube is increased from zero, sketch the tube showing this expansion of length and the positions of the nodes and anti nodes for the first three resonances.