# Section 20.1 Electric Charge and Static Electricity p. 600

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Section 20.1 Electric Charge and Static Electricity p. 600
Ch Electricity Section 20.1 Electric Charge and Static Electricity p. 600 1 1

Electric Charge Causes subatomic particles to attract/repel 2 types
+ and – Everything affected by charge

Neutral atom = protons & e-’s
Gain e-’s = - ion Lose e-’s = + ion Excess/shortage of e-’s produce net charge Coulomb (C) - SI unit of electric charge 6.24 x 1018 e-’s = 1 C

Electric Forces Opposite charges attract
Electric force depends on charge & distance 2x distance = ¼ electric force Stronger than gravity Hold atoms together

Electric Fields The effect electric charge has on other charges
Strength depends on amt of charge producing field & distance from charge Exerts forces on charged object placed in field. More net charge object has, greater force on it

Static Electricity and Charging
net accumulation of electric charges on an object Charge can be transferred by Friction Contact Induction

Static Electricity and Charging
During charge transfer, total charge same before & after transfer Law of conservation of charge

Charging by friction e-’s move from hair to balloon
Atoms in rubber >attraction for e-’s Balloon net – charge Hair net + charge - - + + +

Charging by contact Touch electrically charged object – you become charged Sphere still has net charge, but reduced Van de Graaff generator

Charging by Induction Transfer of charge w/o contact btwn materials
Walk across carpet Pick up extra e-’s; net – charge Repels e-’s in doorknob Leaves net + charge on doorknob closest to hand Doorknob overall charge neutral, but charges moved within it

Static Discharge Occurs when pathway forms for charges to move
Air becomes charged when hand near doorknob Air provides path for e-’s

Static Discharge – lightning
Charge built up from friction btwn moving air masses in clouds - charge in bottom of cloud induces + charge in ground Charge in cloud increases Attraction increases Air charged – pathway for e-’s Lightning 5:06

Electric Current and Ohm’s Law p. 604
Chapter 20.2 Electric Current and Ohm’s Law p. 604

Electric Current Continuous flow of electric charge
SI unit is ampere, or amp (A) 2 types: Direct current (DC) Alternating current (AC)

Direct Current Charge flows in 1 direction
Most battery opperated devices Flashlights Remotes

Alternating Current Current that regularly reverses its direction
Electric current in homes, businesses, & schools often use AC

Electric current in a flashlight
e-’s flow from - to + terminal Current in opposite direction! Scientists define current as direction + charges flow

Conductors material that allows e-’s to flow easily
Metals like copper and silver Made of ions in a lattice ions - atoms that gained or lost e-’s Ions not free to move Each ion has e-’s loosely held Free e-’s conduct charge

Insulators material that doesn’t allow e-’s to move through it easily
e- are tightly held ex: plastic, wood, rubber, glass

Resistance e-’s in electric curent collide opposes flow of e-’s
Tungsten - high resistance e-’s in electric curent collide opposes flow of e-’s electrical energy converted to thermal energy & light measured in ohms () Thickness, length, temp affect resistance

Resistance depends on.. wire thickness
more resistance in thinner wires milkshake in thin v.s. thick straw wire length more resistance in longer wires Temp high resistance at high temps e-’s collide more often

Superconductors Can resistance ever be 0?
Superconductors produce near zero resistance when cooled to low temps.

Voltage Potential Difference (voltage)
diff in electrical potential btwn 2 places in electric field Similar to PE diff of water at top and bottom of fountain large separation of charge creates high voltage Large fountain – high PE “push” causing e- to move from - to + measured volts (V)

Voltage sources Fountains pump water to top, voltage source increases PE of electric charges batteries solar cells generators

Ohm’s Law increasing voltage increases current
Increasing resistance decreases current

A lightbulb with a resistance of 160  is plugged into a 120-V outlet
A lightbulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb? I V R GIVEN: R = 160  V = 120 V I = ?

Electroscope Electroscope
instrument that detects presence of electrical charges leaves separate when they gain + or - charge

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