Question

q15. why must water be degassed each time the ultrasonic cleaners tank is changed?
excess bubbles from filling reduce the energy of the cavitation process
excess bubbles reduce the effectiveness of the detergent
excess bubbles decreased the temperature of the tank
excess bubbles make it difficult to see if items are clean

Explanation:

Ultrasonic cleaners rely on cavitation (formation and collapse of bubbles) for cleaning. Excess bubbles from filling (not degassed water) reduce the energy available for the cavitation process. Detergent effectiveness isn't mainly about filling - stage bubbles. Bubble presence doesn't significantly decrease tank temperature. And while seeing items might be a minor aspect, the core issue for cleaning efficiency is cavitation energy reduction.

Answer:

Excess bubbles from filling reduce the energy of the cavitation process.