You have an empty wine bottle (too bad eh?) with a cork that has been secured at the top in a normal way. There is a metal ring inside the bottle that is suspended by a string.

How can you make the metal ring drop to the bottom if you are not allowed to touch anything - not the bottle, not the cork, not the thread and not the ring?

Science Logic Puzzle

You just need a magnifying glass to do considering you are out in open with bright sun rays available to you. With the glass, you can burn through the string and thus making the ring drop to the bottom.