@cgudrian @marcan Ah, techie tricks on teachers. This one took two weeks. We had an old-fashioned class room with glass in the door and brass door knobs. Week 1 smeared the doorknob with transparent glue (Bostik) and enjoyed teacher's expression through the glass. Week 2 teacher arrives, grins through the glass at us and carefully touches the doorknob with a finger tip. By the time he picked himself off the floor the HUGE and thoroughly charged capacitor had disappeared.