Question

A barometer is constructed with its tube having radius 1.0 mm. Assume that the surface of mercury in the tube is spherical in shape. If the atmospheric pressure is equal to 76 cm of mercury, what will be the height raised in the barometer tube? The contact angle of mercury with glass`135^@` and surface tension of mercury `=0.465Nm^-1`. Density of mercury`=13600kgm^-3`.

Answer 1

Correct Answer - C
`r=1.0mm,
`p=76cm,
`theta=135^@, T=0.4654N/m`
`h=(2Tcostheta)/(rrhog)`
`theta=135^@, t=0.465N/m`
`h=(2xx465xx(1/sqrt2))/(10^-3xx13600xx10)=0.0048m`
`=0.48cm `
=capillary fault due to surface tension
So, height raised in barometer tube
`=H-h=76-0.48=75.52cm`