Question:
The length of a needle floating on water is 2.5 cm. How much minimum force, in addition to the weight of the needle will be needed to lift the needle above the surface of water? Surface tension of water is $ 7.2\times {{10}^{-4}}N/cm $ .
The length of a needle floating on water is 2.5 cm. How much minimum force, in addition to the weight of the needle will be needed to lift the needle above the surface of water? Surface tension of water is $ 7.2\times {{10}^{-4}}N/cm $ .
Updated On: Jun 23, 2023
- $ 7.2\times {{10}^{-4}}N $
- $ 18.0\times {{10}^{-4}}N $
- $ 36.0\times {{10}^{-4}}N $
- none of the above
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The Correct Option is C
Solution and Explanation
: Surface tension $ =\frac{Force}{2(length)} $ $ \therefore $ $ 7.2\times {{10}^{-4}}\frac{N}{cm}=\frac{Force}{2(2.5)\text{ }cm} $ $ \therefore $ Force $ =7.2\times {{10}^{-4}}\times 2.5\times 2\,N $ $ =36.0\times {{10}^{-4}}N $
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Concepts Used:
Surface Tension
The amount of energy required to increase the liquid's surface area by one unit area is known as surface tension. In other words, it is a property of the liquid surface to resist force.
Surface tension is defined as,
The ratio of the surface force F to the length L along which the force acts.
Mathematically, the surface tension formula can be expressed as follows:
T=F/L
Where,
- F is the force per unit length
- L is the length in which force act
- T is the surface tension of the liquid
Read More: Detergents and Surface Tension
Factors affecting surface tension:
- Impurities: The surface tension decreases with the addition of impurities.
- Surfactants: Adding surfactants in liquids lowers the tension of water making it interrupt aside or get susceptible.
- Temperature: The surface tension of a liquid reduces as the temperature rises.
The Unit of Surface Tension:
The SI unit of Surface Tension is Newton per Meter or N/m.