Static Electricity Flashcards
SI Unit of Electric Charge
Coulomb (C)
Charge of 1 electron/proton
1.6 × 10⁻¹⁹ C
How do like and unlike charges react with one another?
Like charges repel, unlike charges attract
What is an Electric Force?
When an electric charge exerts a force on another nearby charge
Properties of an electric force
Can be attractive/repulsive
Gets weaker with distance
What is a Electric Field?
The region where an electric charge experiences an electric force
Electric field of positive charge
Lines go out
Electric field of negative charge
Lines go in
Electrostatic Charging due to Friction
When rubbed, surface atoms are disturbed. Some electrons from surface of one object travel to the other. Object losing electrons becomes positively charged. Object gaining electrons becomes negatively charged. Electrons are easily removed and added to an atom by friction as they are weakly bounded to the atom
Examples of materials with positive charges
Glass, wool, hair, Perspex
Examples of materials with negative charges
Silk, Polythene, Rubber, Wool
What are Conductors?
Materials that have free electrons and are able to conduct electricity (not easily charged by rubbing silk/fur)
What are Insulators?
Materials that do no have free electrons and cannot conduct electricity (electrons are confined at region of rubbing)
Discharging charged insulators and conductors
Earthing
How to discharge a charged insulator?
Heating. Intense heat causes air surrounding insulator to be ionised. These ions in air then neutralise excess charges in insulator
Humid conditions also neutralise a charged insulator over time as water vapour in air helps remove excess charges
What is induction?
Induction is the process of charging a conductor without any contact with charging body
How to charge 2 conductors by induction?
- Let the 2 conductors touch each other
- Bring negatively charged rod near conductor
- Negatively charged rod induces the charges in the 2 conductors, repelling negative charges to the furthest end of conductor B, leaving excess positive charges at the end of conductor A nearest to rod
- Separate the 2 conductors far from each other and remove rod 5. Conductor A is positively charged and conductor B is negatively charged
How do you charge a single conductor?
- Bring positively charged rod near conductor
- Positively charged rod induces the charges in conductor, attracting negative charges to the end of conductor nearest to the rod, leaving behind an excess of positive charges on the other side
- Earth end of conductor which has positive charges
- Negative charges move up the earth and neutralise positive charges
- Remove earth first, then remove rod
- Conductor is negatively charged
What happens when you bring a charged object near an uncharged hanging conductor?
- Positively charged rod induces the charges in other object, attracting negative charges to the end nearest to the rod, leaving an excess of positive charges on the other side
- Since unlike charges are closer than like charges, attractive force is stronger than repulsive force, unlike charges attract and conductor will be attached to the rod
- If conductor touches rod, electrons from conductor will be attracted and move to rod, leaving rod and conductor to have like charges. Like charges repel, conductor will be repelled from the bar
What are the hazards of Electrostatics?
Lightning. Thunderclouds charged by friction with water molecules in clouds and air molecules. Air ionised due to charges. Ionised air provides conducting path for electric charges to be discharged to nearest point in the ground
Electrostatic discharge. Excessive charges built up between objects due to friction. Charges can discharge, causing sparks and ignite flammable items
What are the applications of Electrostatics?
Laser printer
Spray painting cars
Crop pesticide sprayers Electrostatic precipitator to remove ash from power plants
