A tube closed at one end containing air produces, when excited, the fundamental note of frequency $512 \mathrm{kHz}$. If the tube is opened at both ends, the fundamental frequency, that can be excited is (in $\mathrm{Hz}$),

Plane sound waves of wavelength $0.12 \mathrm{m}$ are incident on two narrow slits in a box with non-reflecting walls, as shown. At a distance of $5.0 \mathrm{m}$ from the center of the slits, a first-order maximum occurs at point P which is $3.0 \mathrm{m}$ from the central maximum. The distance between the slits is most nearly