Resistors in Series or in Parallel

Chapter 20 Section 2

Single Resistor AloneIn a circuit that consist of single bulb

and a battery, the potential difference across the bulb equals the terminal voltage.

The current can be found using Ohm’s Law if the resistance is known.

Series Series – Describes a circuit or portion

of a circuit that provides a single conducting path without junctions.

Charges that pass through one resistor must pass through the second resistor and then the third and so on.

All charges follow the same path then it is said to be connected in series.

Series Circuit Diagram

Conservation of ChargeAccording to conservation of charge,

the amount of charge that enters a resistor must equal the amount of charge leaving the resistor.

Resistors that are connected in series, the current in each resistor is the same.

Total ResistanceEquivalent Resistance – The total

resistance of the circuit.The equivalent resistance in a series

circuit is the sum of the circuits resistance.

The equivalent resistance can then be used to find the current in the circuit as long as the voltage is known.

Resistors in Series Equation

Req = Equivalent ResistanceTo find the total current in a series

circuit, first simplify the circuit to a single equivalent resistance

Potential Difference Across Resistors

The potential difference across each resistor is different.

The current across each resistor is constant.

V1 = IR1

V2 = IR2

V3 = IR3

Why Use Series Circuits?Resistors placed in series can

regulate the current in a device.Lots of resistors will make the current

very low.This is why Christmas lights are in series

so the filament doesn’t have to withstand high currents which could cause fires.

Several lesser resistors can make one large equivalent resistor which may not be available.

Parallel CircuitsParallel – Describes two or more

components in a circuit that are connected across common points or junctions, providing separate conducting paths for the current.

The advantage to parallel circuits is that if one of the lights on a strained go out, the rest of the lights remain lit.

Parallel Circuit Diagram

Resistors In Parallel & VoltageResistors in parallel have the same

potential difference across them.The current across the resistors vary

on the strength of resistance.

Resistors in Parallel Equation

1𝑅𝑒𝑞

=1𝑅1

+1𝑅2

+1𝑅3

+…

Resistors in Series or in Parallel

Circuit Type Series Parallel

Schematic Diagram

Current=Same for each resistor

= Sum of currents

Potential Difference (Voltage) =Sum of voltage =Same for each

resistor

Equivalent Resistance =Sum of individual

resistors=Reciprocal sum of resistors