The tube of a mercury barometer is 1 cm is diameter. What correction dur to capillarity is to be applied to the barometric reading if the surface tension of mercury is 435.5 dyn/cm and the angle of contact of mercury with glass is `140^(@)` ?

Explanation

Data : d=1 cm . T = 435.5 dyn/ cm. ` theta = 140^(@)`
` rho = 13660 "kg/m"^(3) = 13.66 "g/cm"^(3)`
` g = 9.8 "m/s"^(2) = 980 "cm/s"^(2)`
` r = d/2 = 0.5 cm, " " cos 140^(@) = - 0.7660` ltbr. ` T = (hr rho g)/(2 cos theta) " " therefore (2 T cos theta)/(r rho g) `
` h = (2xx 435.5 xx (-0.7660))/ (0.5 xx 13.6 xx 980) = - 0.1001 ` cm
The correction due to capillarity = + 0.1001 cm