Ch 4.2 - Electrical Quantities - PART 1

Concepts, Formulas and Important points to remember

Static electricity

Static electricity

The process of charging 2 objects by rubbing them together. The process of charging an object by bringing another charged object near is called Induction.

Static electricity does not include a flow of charges- it is stationary. There is an accumulation of charge. Also ONLY INSULATORS CAN BE USED TO PRODUCE STATIC ELECTRICITY

Conductors & Insulators

Conductors -
Allow flow of charge due to presence of free electrons. Ex- metals- copper or aluminium etc.

Insulators - Do not allow flow of charge due to tightly bound electrons that do not move freely. Ex- wood, plastic or rubber.

Why can only insulators be used to produce static electricity?

Insulators are used because as stated before static electricity does not include the flow of charge. Insulators do not have free electrons hence allowing accumulation of charge

Types of charges

There are 2 types -
Positive charges - obtained by loss of electrons. Positive charge is more than negative

Negative charges - obtained by gain of electrons. Negative charges overweight positive ones

Tendency to gain/loose specific

Tendency to loose and become positive - Hair, Wool, Fur, glass

Tendency to gain - Wood, Paper, balloon, ebonite rod and silk

Charge

The SI unit of charge is coulombs (C). We represent charge by the letter Q

The charge on an electron is - 1.6 × 10^-19 C

Formula of Charge

Q = + OR - ne

Where n is number of electrons and e is the charge of electron which is 1.6 × 10^-19

Law of conservation of charge

Remember, the net charge is always the same before and after induction. There is no net charge because before and after induction sum of charges is same. The net becomes 0 due to balance and cancelling out.

Electric fields and direction

When one charge is placed in the vicinity of another a force is experienced. The region of space where it is experienced is known as an electric field. The direction of electric field at a point is the direction of force on a positive charge