Electricity

What is electricity? The flow of charge Mostly, we focus on the flow of electrons in “normal” matter With static electricity, we get a good “zap” But we cannot stand around all day with Fluffy trying to keep the lights on

Sources of electric charges Chemical Batteries Mechanical Generators Hydro, thermal, nuclear (thermal) Solar Solar cells In every case, the source provides electrons with a “push” that makes it run around in a path (“circuit”)

What is “voltage”? Batteries 1.5V 6V 12V AC electricity 120V 240V 7500V 115000V Voltage is the “push” electrons have in a circuit

What is a circuit? A circuit has three elements A conductor A potential difference or “voltage” A closed loop

An electric circuit is composed of what 3 elements? Conductor, potential difference, closed loop The “push” is called voltage, and is measured in Volts. The flow of electrons is called current, and is measured in Amperes or Amps. The flow of electrons is hindered by resistance, measured in Ohms.

Ohm’s Law Mnemonic

Ohm’s Law: Ohm's Law …says that, for many materials under a wide range of conditions, the voltage, V, and current, I, are linearly related, which implies resistance, R, is independent of V and I. When does it not apply? (Most important case) https://www.youtube.com/watch?v=u4FpbaMW5sk https://www.youtube.com/watch?v=m4jzgqZu-4s

Questions When a battery is connected to a complete circuit, charges flow in the circuit almost simultaneously. Why?

Examples How does this work? http://www.youtube.com/watch?v=0dLTEOM3qQc&feature=related

Electrical Power P= IV “Poison Ivy”

Electrical Energy Hand Generator

Resistance and Ohm’s Law Resistance is the impedance to the flow of charge Resistance is defined as the ratio of potential difference to current R = V/I Unit is the Ohm, Ω A device is said to obey Ohm’s Law of its resistance is independent of the Voltage

Find Resistance of a material Depends on four factors R ∞ Temp R ∞ RHO (ρ) resitivity R ∞ Length R ∞ A-1 (cross-sectional Area)

Low resistance Short Fat cold

High Resistance Long Thin Hot

Diagramming circuits

Series Diagram

Parallel Circuit More than one path for the flow of charge More room for the flow of charge so Resistance goes down Voltage must stay the same since all charges have the same drop