Fused Light-bulb fragile-glass - Ultrasound
In a physics lab at a major university, a very expensive light bulb which would emit precisely controlled quantities of light was being used in some experiments. Ruth was the research assistant responsible for operating the sensitive light bulb. One morning she came into the lab and found to her dismay that the light bulb no longer worked. She realized that she had forgotten to tum it off the previous night. As a result the light bulb overheated, and two wires in the filament inside the bulb fused together. The surrounding glass bulb was completely sealed, so there was no way to open it. Ruth knew that the light bulb could be repaired if a brief, high-intensity ultrasound wave could be used to jar apart the fused parts. Furthermore, the lab had the necessary equipment to do the job.
However, a high-intensity ultrasound wave would also break the fragile glass surrounding the filament. At lower intensities the ultrasound wave would not break the glass, but neither would it jar apart the fused parts. So it seemed that the light bulb could not be repaired, and a costly replacement would be required. Ruth was about to give up when she had an idea. She placed several ultrasound machines in a circle around the light bulb, and administered low-intensity ultrasound waves from several directions all at once. The waves all converged on the filament, where their combined effect was enough to jar apart the fused parts. Since each spot on the surrounding glass received only a low-intensity wave from one ultrasound machine, the glass was left intact. Ruth was greatly relieved that the light bulb was repaired, and she then went on to successfully complete the experiment.