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Question

Liquid rises to a height of 2 cm in a capillary tube. The angle of contact between the solid and the liquid is zero. The tube is depressed more now so that the top of the capillary is only 1 cm above the liquid. Then, the apparent angle of contact between the solid and the liquid is:

A
0
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B
30
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C
60
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D
90
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Solution

The correct option is C 60

We know that,
hR=LR
Also,
R=rcosθ
where r= radius of capillary
θ= contact angle

Let new contact angle be θ.
hrcosθ=Lrcosθ
hcosθ=Lcosθ
2cos0=1cosθ

θ=60
Apparent angle of contact between solid and liquid is 60.

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