Notes

Electric Charge pg 170-177
Positive + negative charges (underlined)
-atoms:
-protons - positive electric charge
-electrons - negative electric charge
-neutrons - no electric charge
-the amount of positive charge on a proton = the amount of negative charge on an electron
-when the positive charge + negative charge cancel out, an atom has no net electric charge
-objects w/ no net charge are said to be electrically neutral
-the amount of electric charge is measured in coulombs (C)
-there are 6,250 million billion protons in 1 C of electric charge; there are 6,250 million billion electrons in -1 C of electric charge
-because electrons are bound more tightly to some atoms + molecules, when a shoe walks on a carpet, electrons transfer from the carpet to the sole of the shoe, the shoe gain an excess of electrons + becomes negatively charged, while the carpet ends up having an excess of positive charge
-static electricity - the accumulation of excess electric charge on an object
-the law of conservation of charge:
charge can be transferred from object to object, but it cannot be created or destroyed
-usually, it is the electrons that transfer from one object to another + not the protons
-Charges exert forces (underlined)
-like magnets, opposite charges attract, whilst like charges repel (charges do not attract or repel particles w/ no charge, such as neutrons, through the electric force)
-the force between electric charges depends on the amount of charge as well as on the distance between charges
-electric field - surrounds every electric charge + exerts the force that causes other electric charges to be attracted or repelled
-any charge that is placed in an electric field would make a positive charge move (electric charges don't need to be touching to exert forces on each other)
-electric field arrows point away from positive charges + toward negative charges
-compared w/ electric forces, the force of gravity is very weak
-Conductors + insulators (underlined)
-conductor - a material through which electrons move easily
-skin is an effective conductor
-best conductors: metals
-insulator - a material in which electrons are not able to move easily
-glass: an insulator
-electrons are held tightly to the atoms that make up insulators
-most plastics: insulators
-Charging by contact (underlined)
-charging by contact - the process of transferring charge by touching or rubbing
-if you rub 2 materials together, it can result in a transfer of electrons, resulting in on material left w/ a positive charge + the other w/ an equal amount of negative charge
-Charging by induction (underlined)
-because electric forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object
-charging by induction - the rearrangement of electrons on a neutral object caused by a nearby charged object
-Lightning (underlined)
-static discharges - a transfer of charge between 2 objects because of a buildup of static electricity (lightning, getting shocked, etc.)
-thundercloud: a mighty static electricity generator
-as air masses move + swrl in the cloud, areas of positive + negative charge build up
-eventually, enough charge builds up to cause a static discharge between the cloud + the ground
-as the electric charges move through air, they collide w/ atoms + molecules, which cause the atoms + molecules in the air to emit light (the flash of lightning)
-lightning produces sound waves as well as a brilliant flash of light
-the electrical energy in a lightning bolt ripis electrons off atoms in the atmosphere + produces great amounts of heat. the surrounding air temperature can rise to =~ 30,000^oC, severe times hotter than the Sun's surface. the heat causes air in the lightning bolt's path to expand rapidly, producing sound waves that you hear as thunder
-a discharge can occur any time that charge builds up in one area
-providing a path for charge to reach Earth prevents any charge from building up (lightning)
-Earth: neutral object, conductor of charge
-grounding - connecting an object to Earth w/ a conductor
-Electroscopes (underlined)
-electroscope - a device that can detect electric charge
i i
| --> |
|^| /^
-if a negatively charged object touches the knob, electrons will travel down the rod into the leaves. Both leaves become negatively charged as they gain electrons, resulting in them repelling each other
-if a positively charged object touches the knob, the same thing will happen, as both metal leaves will still have the same charge