Practice portal › Mechanical Properties of Fluids › Surface Tension and Surface Energy

The surface tension of a soap bubble is 2.0×10⁻² N m⁻¹. The work done to increase the radius of the soap bubble from 3.5 cm to 7 cm will be (take π=(22)/7)

Asked in JEE Main 29th Jan 1st Shift 2023 · Work done on a soap bubble

• (1) 9.24×10⁻⁴ J
• (2) 18.48×10⁻⁴ J
• (3) 0.72×10⁻⁴ J
• (4) 5.76×10⁻⁴ J

Step-by-step solution

Why the other options are wrong

• (1) comes from counts only one surface, 4π T(r₂²-r₁²)=9.24×10⁻⁴ J; a bubble in air is a film with an inside face and an outside face, so the area to be created is doubled.
• (3) comes from no consistent slip lands here; 0.72×10⁻⁴ J is below even the one-surface value 9.24×10⁻⁴ J, and nothing in 8π T(r₂²-r₁²) shrinks the answer that far.
• (4) comes from a filler near the value 8T(r₂²-r₁²)=5.88×10⁻⁴ J that comes from dropping π altogether — near it, but not equal to it, so nothing clean lands on 5.76×10⁻⁴ J.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.