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A glass capillary tube is of the shape o...

A glass capillary tube is of the shape of a truncated cone with an apex angle `alpha` so that its two ends have cross sections of different radii. When dipped in water vertically, water rises in it to a high h, where the radius of its cross section is b. If the surface tension of water is S, its density if `rho`, and its contact angle with glass is `theta`, the value of h will be (g is the acceleration due to gravity)

A

`(2S)/(brhog)cos(theta-alpha)`

B

`(2S)/(brhog)cos(theta+alpha)`

C

`(2S)/(brhog)cos(theta-alpha//2)`

D

`(2S)/(brhog)cos(theta+alpha)`

Text Solution

Verified by Experts

The correct Answer is:
D
Let r= radius of curvature of meniscus `b=r"cos"(theta+(alpha)/(2))`
Excess pressure on concave side of meniscus`=(2S)/(r)`
`implies (P_(0)+hrhog)-P_(0)=(2S)/(r)`
`implies hrhog=(2Scos(theta+(alpha)/(2)))/(b)`
or `h=(2S)/(brhog)"cos"(theta+(alpha)/(2))`
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Knowledge Check

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