At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work?

a. A comb run through one's dry hair attracts small bits of paper. Why? What happens if the hair is wet or if it is a rainy day? (Remember, a paper doesn't conduct electricity.) b. Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary? c. Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why? d. A bird perches on a bare high power line, and nothing happens to the bird. A man standing on the ground touches the same line and gets a fatal shock. Why?

The simplest example of simple harmonic motion is the oscillations of a simple pendulum. In a simple pendulum made of a metallic wire, what will happen to the period when temperature increases? Give a reason.