Electric Charges and FieldsIntroduction
It is a dry January evening in Delhi. Riya pulls off her woollen sweater in a dark room, and it crackles with tiny blue sparks. The next morning, as she slides off her seat and grabs the steel rail to get down from the bus, a sharp little sting jumps into her fingers. And every monsoon the sky does the same thing on a gigantic scale: lightning.
What is behind the crackle, the sting and the lightning?
Rubbing insulating things together, a woollen sweater against a shirt or a seat cover against your clothes, piles up electric charge. The charge stays put until it finds a path: then it rushes away in a discharge, as a spark through the air or as a sting through your body to the ground. You may have heard this called static electricity. Static means not moving or changing with time, and electrostatics is the study of the forces, fields and potentials of charges at rest. This chapter and the next are all about it.