CBSE Class 11-science Answered
Sir/madam
I have a question. How can we say that water spreads on glass easily inspite of its low surface tension. Also how can we say that the interface of mercury-glass does not spread on glass easily inspite of its high surface tension?????plz reply quickly!!!
Asked by shravan s | 02 Dec, 2013, 11:48: AM
Expert Answer
How easily a liquid drop spreads on a solid surface depends on contact angle.
A contact angle less than 90° (low contact angle) usually indicates that wetting of the surface is very favorable, and the fluid will spread over a large area of the surface. Contact angles greater than 90° (high contact angle) generally means that wetting of the surface is unfavorable so the fluid will minimize contact with the surface and form a compact liquid droplet.
The angle of contact between water and glass typically lies in the range 
to 
, whereas that between mercury and glass is about 
to , whereas that between mercury and glass is about Therefore, mercury does not spread easily on glass surface while water spreads easily on it.
|
Contact angle |
Degree of wetting |
|
θ = 0 |
Perfect wetting |
|
0 < θ < 90° |
high wettability |
|
90° ≤ θ < 180° |
low wettability |
|
θ = 180° |
perfectly |
Answered by Komal Parmar | 02 Dec, 2013, 03:02: PM
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