Introduction

Introduction

Consider the activity of rubbing a balloon against our hair. We notice that after rubbing the balloon, the balloon can now stick to the wall. What really happens? The answer to this question lies in phenomena called static electricity.

• If you charge a balloon by rubbing it on our hair, it picks up extra electrons and acquires a negative charge.
• Holding it near a neutral object will make the charges in that object move. If it is a conductor, many electrons move easily to the other side, as far from the balloon as possible.
• If it is an insulator, the electrons in the atoms and molecules can only move very slightly to one side, away from the balloon.
• In either case, there are more positive charges closer to the negative balloon. Opposites attract each other, and hence the balloon sticks to the wall (at least until the electrons on the balloon slowly leak off).

STATIC ELECTRICITY

The static electricity refers to the buildup of electric charges on the surface of objects. We can also say that static electricity refers to stationary electric charges, typically produced by friction, which causes sparks or crackling or the attraction of dust or hair.

Scientists have ranked materials in order of their ability to hold or give up electrons. This ranking is called the triboelectric series. A list of some common materials are shown here. Thus, if two materials are rubbed together, the one higher in the list should give up electrons and become positively charged.

THE TRIBOELECTRIC SERIES

OUR HAND
GLASS
OUR HAIR
NYLON
WOOL
FUR
SILK
PAPER
COTTON
HARD RUBBER
POLYESTER
POLYVINYL CHLORIDE
PLASTIC

ELECTRIC CHARGES

Electric charge is the basic physical property of matter that causes it to experience a force when kept in an electric or magnetic field.

TYPES OF CHARGES

There are two types of charges.

1. Positive charge
2. Negative charge

Properties:

• Like charges always repel each other whereas unlike or opposite charges always attract each other.
• The SI unit of charge is Coulomb and is denoted by C.
• The smallest possible negative charge is an electron and that of positive charge is proton.
  • Charge on an electron is -1.6×10^-19C
  • Charge on a proton is  +1.6×10^-19C
• Since only an integral number of electrons can be transferred from one object to the other on rubbing. Hence, we say that charge is quantized.

or,  Q=ne , and n=1, 2, 3 ……

where Q is the total amount of charge on a charged body, n is the number of electrons and e is the charge on an electron.

Example: Calculate the number of electrons in  of charge.

Solution: Given,

Total charge  Q = 1C
Charge on an electron e = 1.6×10^-19C (neglecting the negative sign)
Number of electrons n = ?

Therefore, there are   6.25×10¹⁸C  electrons in 1C  and we should remember this data as this will make our calculation in further questions easy.