Static Electricity Ms. Petrauskas

Static Electricity An imbalance of electric charge on the surface of an object Static means stationary or non-moving

Electric charge A form of charge either positive or negative that exerts an electric force Ex. When an atom is not neutral A ‘+’ symbol represents a large number of protons an a ‘-’ symbol represents a large number of electrons Shows the distribution of charges in an object

Law of Electric Charges Like charges repel Opposites attract Any charge attracts neutral + + + - + - +

Laws continued The strength of the electric force is directly related to the strength of the charges on each object Decreases with distance between objects

Pithball electroscope Detects charge Pithball is neutral and if the object is charged then the pithball will be attracted to it.

Neutral Attraction As a charged object is brought close to a neutral object it causes (induces) a rearranging of electrons Inducing a movement of electrons is called induced charge separation Charge not permanent!

Metal Leaf Electroscope More sensitive than pith ball when detecting electrical charge When a charge is transferred (by contact or by induction) the leaves receive the same charge and therefore repel each other

Charging by friction When two objects of different materials rub against each other, they produce a net static charge

Electrostatic Charges One material has a stronger attraction to electrons than another material, and therefore pulls those electrons away resulting in a negative charge The material that loses electrons becomes positively charged Most object are electrically neutral

Electrostatic Series A list of materials arranged by their likelihood to attract electrons Used to predict resulting charges from contact

Examples: see page 473 What is the resulting charge when ebonite and rabbit fur are rubbed together? Nylon and wool? Which would have a stronger resulting charge?

Insulators and Conductors Insulator: electrons do not move freely between atoms in this material Wood, rubber, wax Conductor: electrons move freely from atom to atom in this material Metal, tap water Semi- conducter: electrons can move fairly well in these non-metal materials Silicone, mixtures of arsenic, selenium and tellurium

Charging by Contact Aka charging by conduction When two objects with different amounts of charge come into contact and electrons move from one object to another “ electrons distribute” The neutral object takes the charge of the charged object SO when a + touches a neutral object the object become + and when - touches neutral it becomes -

Neutral Object becomes negative Negatively charged

Neutral becomes positive

Grounding Removing a net static charge by putting it into contact with the ground Has a large number of electrons and can either supply or remove Earth is so huge, it can do this without affecting its overall charge

Grounding = Neutralizes Electrons move toward the earth Electrons move up to neutralize

Shocks & Sparks When a large number of electrons flow rapidly between objects (more often with a conductor) Ex. When wearing cotton socks and you walk across a polyester carpet and then touch a doorknob= SHOCK!. What charge do your socks become? Positive When you touch a conductor like a doorknob, electrons quickly flow into you, to neutralize your charge, causing a shock or spark Avoid by slowly releasing electrons with a insulator “ground” Grounding is used in the following situations Operating rooms Fuel trucks Lightning Appliances

Applications Dryer sheets Higher humidity Grounding electronics waxy coating equals charges so there is no transfer of electrons, no static Higher humidity more water in air and charges removed quickly through collisions because of the close proximity with water vapour Grounding electronics Third prong is a ground. Shocks and sparks can damage equipment and/or cause fires

Precipitator- remove pollution particles from air in power plants Precipitator- remove pollution particles from air in power plants. Particles pass by negatively charged plates and become negative by contact. They then pass positive plates and stick. Electrostatic duster- sweep across the ground, creates a build-up of charge, dust “jumps” from dusty surface to duster