Resistors in Series or in Parallel
Chapter 20 Section 2
Single Resistor Alone
In 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 Charge
According 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 Resistance
Equivalent 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 Circuits
Parallel – 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 & Voltage
Resistors 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