What is electricity?
•The flow of charge
•Mostly, we focus on the flow of electrons in “normal”
•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
•Hydro, thermal, nuclear (thermal)
•In every case, the source provides electrons with a
“push” that makes it run around in a path (“circuit”)
What is “voltage”?
•Voltage is the “push” electrons have in a circuit
What is a circuit?
A circuit has three elements
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
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)
When a battery is connected to a complete circuit,
charges flow in the circuit almost simultaneously.
How does this work?
P= IV “Poison Ivy”
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
on four factors of a material
R ∞ Temp
R ∞ RHO (ρ) resitivity
R ∞ Length
R ∞ A-1 (cross-sectional Area)
More than one path for the flow of charge
More room for the flow of charge so Resistance goes
Voltage must stay the same since all charges have the