Chapter 21

Electricity

Opposite charges attract, like repelCharged objects can cause electrons to rearrange their positions on a neutral object

Three methods of charging objects with static electricity

1. Friction- movement of electrons caused by rubbing

2.Conduction: flow of electrons by direct contact

Conductor: material that allows electrons to move easily through it (metals)

Insulator: material that doesn’t allow electrons to move through it easily (plastic, rubber, glass, wood, and air)

3. Induction- rearrangement of electric charges

Static Electricity: accumulation of electric charges on an object and is stationary or not moving

Loosely held electrons are transferred from one object to another

Electric Discharge-The loss of static electricity as electrons move off an object and usually into the airLightning Shocking someone after rubbing your feet as you walk on carpet in the winter

Section 2

Lightning: very large discharge of static electricity

Billions and billions of electrons

Circuit: closed path through which electrons can flow

Current: flow of electrons through a wire or conductor

Ampere

Series circuit: current has only one path it can travel

When any part of a series circuit is disconnected, no current can flow through the circuit (Christmas lights)

Parallel Circuit: contain separate branches for current to move through

When one branch is open, the current continues to flow through the other branches

Parallel Circuit: contain separate branches for current to move through

Electroscope: device that detects the presence of an electric charge

Two thin metal leaves attached to a metal rod with a knob at the top

The two leaves move away from each other when they become charged

Lightning Rod: device that is grounded to the Earth so that it can carry lightning harmlessly to the ground

Section 3

Electrons flow from places of higher potential energy to those with lower until equal

Potential difference: difference in potential between two different places

Volts (v)

Batteries

Dry Cell: “electron pump” because it has a potential difference between the positive and negative terminals

Continues as long as the chemical reaction occurs

Batteries

Wet Cell: two connected plates made of different metals in an electrolyte solution

Ex. Car battery

Resistance: tendency for a material to oppose the flow of electronsOhms ()

Material, size & length, temperature all affect resistance

Ohm’s Law: current in a metal conductor is directly proportional to the potential difference across its ends & inversely proportional to the resistance

V (volts) = I (amperes) x R (ohms)

Practice Problems 1 & 2 (pg. 558)

Either a fuse or a circuit breaker is wired between every parallel circuit and the main switch box

Fuse – melts Breaker - bends

Section 5

Electrical Power: rate at which electrical energy is converted to another form of energy (W) watts

Power = current x voltageP = I x V

Practice Problems 1 & 2 (pg. 566)

Kilowatt- hour: 1000 watts of power used for one hour

Energy = power x timeE = P x t

Practice Problems 1 & 2 (pg. 568)