Logic Puzzles

These are not brain teasers and don't require much of knowledge of mathematics. Just common sense is enough to solve each of these.

Have fun solving puzzles!

1. A man who lives on the tenth floor takes the elevator down to the first floor every morning and goes to work. In the evening, when he comes back; on a rainy day, or if there are other people in the elevator, he goes to his floor directly. Otherwise, he goes to the seventh floor and walks up three flights of stairs to his apartment. Can you explain why? (Courtsey Harshvardhan Mandad)

This puzzle is taken from the movie Fermat's Room(nice movie)

2. There are two rooms. In one of the room A, there are three light bulbs and in another room B, there are three switches corresponding to these bulbs. Initially, you are in the room B
How can you identify which switch correspond to which bulb with just one trip to room A.

3. How can you throw a ball as hard as you can and have it come back to you, even if it doesn't bounce off anything? There is nothing attached to it, and no one else catches or throws it back to you.

4. You are in a room with no metal objects except for two iron rods. Only one of them is a magnet. How can you identify which one is a magnet?