# gr 9 science study notes

Topics: Electric charge, Electricity, Electrostatics Pages: 6 (1970 words) Published: December 12, 2014
﻿Static electricity: electric charge that builds up on the surface of an object

Friction: is the force resisting the relative motion of two surfaces in contact When two objects are rubbed together there is more contact between the surfaces and so more electrons are transferred

Electron Affinity:
Electron affinity is the tendency of a substance to hold onto electrons.

Items high on the list (electrostatic/ triboelectric series) will tend to lose electrons easily (positive) Items low on the list will tend to gain electrons easily, or hold on to their electrons

example: glass rubbed with plastic wrap
glass is above plastic wrap
glass will become positive and plastic wrap will become negative

Conductivity is the ability of materials to allow electrons to move freely in them Insulators: are solids, liquids, or gases that resist or block the movement of electrons Conductors: are materials that allow electrons to move freely.

Law of Attraction: states particles with opposite charges attract each other. (unlike charges attract) Law of Repulsion: states that particles with like charges repel each other. (like charges repel) -charged objects attract neutral objects, neutral objects show no reaction towards neutral objects

Charging by contact
-contact of the rod with the electroscope will cause a transfer of electrons and leave a permanent charge on the electroscope -the charge on the electroscope will be identical to that on the rod

Charging by Induction
-the movement of electrons within a substance caused by a nearby charged object. There is no direct contact. -a charged object is used to induce a charge in a neutral object and then the object is grounded so that charge is retained -Grounding is the process of connecting a charged object to the Earth's surface. A conductor (a finger) allows charges/ electrons to travel to or from ground -the charge on the electroscope will be opposite of the charge on the rod used in induction

Electrical discharge- an object is discharged when it loses its excess charges either by sparking or grounding. Sparking: electric charges are transferred very quickly -when an object is charges the charges are trapped on it until it is given a pathway to leave. Whenever they transfer very quickly the process is called electrical discharge. (e.g when you walk across a carpet and touch a metal doorknob.)

Detecting Static Charge
-if you have an object with an unknown charge you can determine its charge by bringing an object with a known charge next to it or by using an electroscope with a known charge -use known materials (from the triboelectric series) to attain a known charge and use the laws of attraction and repulsion or use a neutral electroscope

When a negative rod is brought near a neutral electroscope:
-electrons are repelled and move to the leaves
-leaves are both negative and repel
-if the rod does not touch the nob and is removed the electroscope will return to original neutral state

Lightning
-a very large electrical discharge caused by induction
-negative charges that have built up at the base of moving cloud create a temporary positive area on the ground below the cloud -when enough charge builds up on the cloud, it discharges in the form of lightning

Lightning awareness
-the longer it takes thunder to be heard after lightning is seen means the storm is farther away from you -if you can hear thunder, lightning is within striking distance of you -take shelter in tall buildings that are grounded

-take shelter in vehicles with windows rolled up and dont touch any metal parts of the vehicle -avoid the highest points of land as they are induced first
-do not stand under trees, as they tend to be induced first
-stay away from conductive materials like bikes

Lightning rod
-metal pole with a wire attached that conducts excess charge like lightning into the ground

Making use of static charges
-spray paint coming out of a nozzle is given a...