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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

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Length of the plate, l = 10 cm =0.1 m
Thickness, t = 0.4 cm = 0.004 m
Forces acting on the plate when it just touches the surface of water.
(i) Weight of the plate, IV = mg
(40g)(9.8m`s^(.2)`)
`0.04xx9.8 N `
0.392 N
Weight acts downward.
(ii) Force due to surface tension
`F = S xx 2`(tength + thickness)
= 0.073 x 2(0.1 + 0.004)
= 0.073 x 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
0.407N
Therefore, apparent weight of the plate W =,W+ F
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