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JEE Advanced · Physics · 11. Properties of Fluids

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

  1. A 2Sbρgcos(θ-α) 
  2. B 2Sbρgcosθ+α
  3. C 2Sbρgcosθ-α2
  4. D 2Sbρgcosθ+α2
Verified Solution

Answer & Solution

Correct Answer

(D) 2Sbρgcosθ+α2

Step-by-step Solution

Detailed explanation

If R be the meniscus radius,
Rcosθ+α2=b
Excess pressure on concave side of meniscus =2SR

hρg=2SR=2Sbcosθ+α2
h=2Sbρgcosθ+α2
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