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A square glass plate of length 10 cm and...

A square glass plate of length 10 cm and thickness 0.4 cm, weight 40 g in air. It is held vertically such that its lower edge rests on water surface. What is the apparent weight of glass plate now? (Given surface tension of water = 0.073 N `m^(-1)`)

Text Solution

Verified by Experts

Length of the plate, `l = 10 cm = 0.1 m`
Thickness, `t = 0.4 cm = 0.004 m`
Forcess acting on the plate when it just touches the surface of water.
(i) Weight of the plate, W = mg
`= (40 g) (9.8 ms^(-2))`
`= 0.04 xx 9.8` N
= 0.392 N
Weight acts downward.
(ii) Force due to surface tension
F = S `xx` 2 (length + thickness)
= 0.073 `xx` 2(0.1 + 0.004)
= 0.073 `xx 0.208 N
0.015 N
Since the angle of contact is acute in this case, this force acts downwards.
Therefore, apparent weight of the plate W' = W + F
0.392 + 0.015 N
= 0.407 N
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