WAEC - Physics (2017 - No. 18)
The diagram above illustrates a beaker of water being heated. It is observed that as the bubbles rise they get bigger in size.The reason for this observation is
water pressure on the bubbles decreases
density of water increases with rise in temperature
volume of water increases with rise in temperature
atmospheric pressure on the bubbles decreases
Paliwanag
When a bubble is deep under water, it has both atmospheric pressure and water pressure (giving it depth), acting on it but as it rises, the water pressure decreases. At this point, the basic pressre acting on the bubble is the atmospheric pressure. Recall that pressure is inversely proportional to volume (Boyles' law), hence, the less the pressure, the more the volume.