When a cylindrical capillary glass tube, open at both ends, is vertically inserted in a pool of water, the water level in the tube rises to $7 \mathrm{~cm}$ relative to the water level outside the tube. Consider that the surface tension of water is $0.07 \mathrm{~N} \mathrm{~m}^{-1}$ and that the contact angle of water on glass is $0^{\circ}$. The density of water is $1000 \mathrm{~kg} \mathrm{~m}^{-3}$, and the local acceleration due to gravity is $10 \mathrm{~m} \mathrm{~s}^{-2}$. The diameter of the capillary tube (in $\mu \mathrm{m}$ ) is $\_\_\_\_$ (rounded off to the nearest integer).
