Question:
When one end of the capillary is dipped in water, the height of water column is 'h'. The upward force of 108 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of the capillary is (surface tension of water $=7.2\times10^{-2}N/m$)
When one end of the capillary is dipped in water, the height of water column is 'h'. The upward force of 108 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of the capillary is (surface tension of water $=7.2\times10^{-2}N/m$)
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$1$ Newton $= 10^5$ dyne. Always double-check unit conversions in surface tension problems.
Updated On: Jun 21, 2026
- 3 cm
- 2.5 cm
- 1.8 cm
- 1.5 cm
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The Correct Option is D
Solution and Explanation
Step 1: Concept
The upward force due to surface tension is $F = T \times L$, where $L$ is the contact length (circumference).
Step 2: Conversion
- Force $F = 108$ dyne $= 108 \times 10^{-5}$ N. - Surface tension $T = 7.2 \times 10^{-2}$ N/m.
Step 3: Calculation
$L = F/T = \frac{108 \times 10^{-5}}{7.2 \times 10^{-2}} = \frac{108}{7.2} \times 10^{-3} = 15 \times 10^{-3}$ m.
$L = 1.5$ cm.
Step 4: Conclusion
Hence, the inner circumference is 1.5 cm. Final Answer: (D)
The upward force due to surface tension is $F = T \times L$, where $L$ is the contact length (circumference).
Step 2: Conversion
- Force $F = 108$ dyne $= 108 \times 10^{-5}$ N. - Surface tension $T = 7.2 \times 10^{-2}$ N/m.
Step 3: Calculation
$L = F/T = \frac{108 \times 10^{-5}}{7.2 \times 10^{-2}} = \frac{108}{7.2} \times 10^{-3} = 15 \times 10^{-3}$ m.
$L = 1.5$ cm.
Step 4: Conclusion
Hence, the inner circumference is 1.5 cm. Final Answer: (D)
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