Question

An air bubble in a water tank rises from the bottom to the top. Which of the following statements are true?[Assume tank is maintained in isothermal condition]

• A. Bubble rises upwards because pressure at the bottom is less than that at the top.
• B. Bubble rises upwards because pressure at the bottom is greater than that at the top.
• C. As the bubble rises, its size remains same
• D. As the bubble rises, its size decreases

Answer 1

The correct option is B Bubble rises upwards because pressure at the bottom is greater than that at the top.

$P_{\text{Bottom}}>P_{\text{Surface}}$ . So the bubble rises upward.
At constant temperature $V\propto \frac{1}{P}$ (Boyle’s law)
Since, the bubble rises upward, pressure decreases, then from above law volume of the bubble will increase i.e. its size increases.