The lower end of a capillary tube is dipped into water and it is seen that the water rises through 7.5 cm in the capillary. Find the radius of the capilary. Surface tension of water `=7.5xx10^-2Nm^-1`. Contact angle between water and glass `=0^@. Take g=10ms^-2`.

Options

A. 0.2 cm
B. 0.1 cm
C. 0.4 mm
D. 0.2 mm

Answer

D

Explanation

Given, height raised by liquid,
`h=7.5 cm= 7.5 xx 10^(-2)` m
Surface tension, S`=7.5 xx 10^(-2)Nm^(-1)`
and contact angle, `theta=0^(@)`
As `r=(2Scostheta)/(hrhog)`
where, `rho`=density of water `=1000kgm^(-3)`
`rArr r=(2 x x 7.5 xx 10^(-2) xx cos0^(@))/(7.5 xx 10^(-2) xx 1000 xx 10)` ltbgt `=2/10 xx 10^(-3)m=0.2mm`