Chapter 17 Static Electricity Static Electricity Electrostatic Phenomena

Chapter 17: Static Electricity:

Static Electricity: Electrostatic Phenomena Have you ever experience: You walk across the rug, reach for the doorknob and. . ZAP!!! You get a shock. WHY?

Static Electricity: Electrostatic Phenomena OR have you ever experience: You come inside from the cold, pull off your hat and. . . BOING!!! All your hair stands on end. What is going on here? And why does it only happen in the winter?

Static Electricity: Electrostatic Phenomena

Static Electricity: Electrostatic Phenomena

Static Electricity: Electrostatic Phenomena

Static Electricity: Electrostatic Phenomena Summary

Static Electricity: Structure of an atom

Static Electricity: Insulators & Conductors

Static Electricity: Neutralising Charged Conductors

Static Electricity: Neutralising Charged Conductors

Static Electricity: Charging by Induction

Static Electricity: Charging by Induction

Static Electricity: Charging a single conductor

Static Electricity: Charging a single conductor

Electric Field: Unit of Charge – The Coulomb (C) The Coulomb is the quantity of electric charge that passes through a given section in a circuit when a steady current of one ampere flows for one second.

Electric Field: Unit of Charge – The Coulomb (C) Unlike Charges Like Charges

Electric Field: Coulomb’s Law The electrostatic force of interaction between two charged particles is proportional to the product of their charges and inversely proportional to the square of their separation, and its direction is along the line joining the two charges. Where є=8. 85 x 10 -12 C 2 N-1 m-2

Electric Field: An Electric Field exists in a region of space where a small positive charge experiences an electric force. The direction of the field is defined as the direction of the force on a small positive charge.

Electric Field: An Electric Field exists in a region of space where a small positive charge experiences an electric force. The direction of the field is defined as the direction of the force on a small positive charge.

Electric Field: An electric dipole

Practical Application of Electrostatics: 1. Electrostatic Precipitator

Practical Application of Electrostatics: 2. Spray Paint

Practical Application of Electrostatics: 3 a. Photocopier Drum coated with Selenium, a photoconductor White parts of paper reflect lot of light to some part of drum, making these areas conducting and loses charges

Practical Application of Electrostatics: 3 b. Photocopier Fine particles of carbon powder (toner) are attracted to charged area of the drum

Potential Hazards with Electrostatics 1 a. Lightning • Friction between clouds and wind causes the cloud to be charged NEGATIVELY • Highly Charged clouds ionise the air around it • Air becomes a conductor to these charges • Charges flow through the air to the earth at very high speeds, giving off light • Charges take the shortest path http: //weathereye. kgan. com/cadet/lightning/bigspark. html

Potential Hazards with Electrostatics 1 b. Lightning • Lightning conductors are fitted on top of buildings • When thunderclouds are nearby, positive charges are induced on lightning conductors • Induced positive charges remove electrons from the nearby air and ionise surrounding air • Positive charged air flow upwards to neutralise thundercloud

Potential Hazards with Electrostatics 1 c. Lightning Rod • Charge flows readily to or from sharp metal points • Point of the rod collects electrons from the air, preventing large buildup of positive charge on the building by induction. • Continual “leakage” of charge prevents a charge buildup that might lead to sudden discharge between the cloud and building Purpose of lightning rod: To prevent a lightning discharge. Hence, to prevent a fire caused by lightning!

Potential Hazards with Electrostatics 1 c. Lightning Rod • Lightning rod collects the electrons from the bottom of the cloud and discharges them, preventing a large discharge in the form of lightning. Should a discharge occur, the sharp point causes a concentration of positive charge at the tip, attracting the lightning and conducts the electrons to the ground, preventing damage to the building

Potential Hazards with Electrostatics 2. Fires and explosions • Tyres of moving truck acquires negatively charges by friction from the road • Metal body near tyres become positively charged by induction • Sparks may be produced • Metal chain at the rear end conducts electrons from ground to neutralise positive charges on the metal body of truck It also allows the truck to discharge excess charge •

Van De Graaff Generator • Charges on surface of dome cause the air nearby to be ionised, making the air partially conducting • A pathway for charges on the dome to leak off into the air, causing “Lightning”

Electrostatic – Shock! • When your shoes scuff against the rug, your shoes are actually picking up electrons from the rug. • The electrons move over your body, giving you a negative charge. • If you touch a metal doorknob, the electrons on your body will leap into the metal, attracted by the protons there. • The transfer of electrons is actually a small electrical current, and produces the tiny electric shock you feel. http: //weathereye. kgan. com/cadet/lightning/electricity. html#s tatic

Electrostatic