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Question:

The following observations were taken for determining surface tension T of water by capillary method: diameter of capillary, D = 1.25 × 10⁻⁶ m; rise of water, h = 1.45 × 10⁻⁶ m. Using g = 9.80 m/s² and the simplified relation T = rhg/2 × 10³ N/m, the possible error in surface tension is closest to:

0.15

2.4

10

1.5

Solution:

T = rhg/2 × 10³ N/m = Dhg/4 × 10³ N/m (Since D = 2r)
⇒ logT = logD + logh + logg + 3
⇒ ΔT/T = ΔD/D + Δh/h = 0.01/1.25 + 0.01/1.45 = 0.015 = 1.5%