I was photographing landscapes in a field under high tension power lines (see photo) when I discovered my metal tripod was delicately vibrating. I could only feel the vibrations if I rested my fingers lightly on the metal and they were clearly related to the high tension wires (not the gentle breeze). When I moved the tripod away from the lines the vibrations stopped, but returned when I took it back beneath the wires again. What was going on? More importantly, if the lines did this to a metal tripod, what might they have been doing to my body?

Alistair Scott, Gland, Switzerland

If you played the same note, in 500 versions of exactly the same speakers (so all the same frequencies) at the same distance from the receptor (ear or decibel meter), would it be the same volume? 

If it would increase, how much by and why? 

Would it be 500 times? Or would some be cancelled out?

Thanks!

On a number of brush metal laptops/appliances if you run your finger lightly across the surface it creates a vibration sensation in your fingertip; this is not friction it is an actual vibration, I can categorically say that it is caused by some kind of electrical interaction is that the sensation only happens when your appliance is plugged into the AC power which suggest it is something to do with the frequency of AC power, but my question relates to the actual interaction between the metal surface and my finger, what is causing the feeling?