JEE Main · 2026 · 22 Jan 2026 · Shift 2 · Fluid Mechanics

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When a part of a straight capillary tube is placed vertically in a liquid, the liquid raises upto certain height h. If the inner radius of the capillary tube, density of the liquid and surface tension of the liquid decrease by

1%

each, then the height of the liquid in the tube will change by

____

(A)-1
(B)+3
(C)-3
(D)+1✓ Correct

Answer: (D)

Solution

The capillary rise is

h = \frac{2 T cos θ}{ρ g r}

, so for small changes the percentage changes combine as

\frac{Δ h}{h} = \frac{Δ T}{T} - \frac{Δ ρ}{ρ} - \frac{Δ r}{r} .

Each of

T

ρ

and

r

decreases by

1%

, so

\frac{Δ h}{h} = (- 1) - (- 1) - (- 1) = + 1%

. The height of the liquid increases by

1%

JEE Main · 2026 · 22 Jan 2026 · Shift 2 · Single correct option

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