Q23. A liquid column of height 0.04 cm balances excess pressure of a soap bubble of certain radius. If density of liquid is $8 \times 10 ^ { 3 } \mathrm {~kg} \mathrm {~m} ^ { - 3 }$ and surface tension of soap solution is $0.28 \mathrm { Nm } ^ { - 1 }$, then diameter of the soap bubble is $\_\_\_\_$ cm . (if $g = 10 \mathrm {~m} \mathrm {~s} ^ { - 2 }$ )