An electric circuit is composed of 3 elements

• Conductor, potential difference, closed loop

• An electrical circuit without a load that has some resistance is essentially a short circuit

•(Think about the batteries in the simulation)

•(An ammeter has very little resistance. Think about my poor ammeters in a circuit with no loads or other resistance.)

Electrical Circuits

In a series electric circuit all of the electrons must flow through the same elements

In a parallel electric circuit electrons may flow through different circuit elements

Electrical Circuits

In a series electric circuit, the voltage drops as it flows through each resistive circuit element

Electrical Circuits

Resistors in Series: Building Analogy

To go from the top to the bottom floor, all people must take the same path. So, by definition, the staircases are in series. With each flight people lose some of the potential energy given to them by the elevator, expending all of it by the time they reach the ground floor. So the sum of the V drops across the resistors the voltage of the battery. People lose more potential energy going down longer flights of stairs, so long stairways correspond to high resistance resistors.

The double waterfall is like a pair of resistors in series because there is only one route for the water to take. The longer the fall, the greater the resistance.

3 steps

6 steps11 steps

Elevator (battery)

R1 = Lamp

R2 = Lamp

R3 = Lamp

R1

R2

Diagramming circuits

Series Diagram

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)

Ohm’s Law Mnemonic

Questions

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

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

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