Series & Parallel Circuits

2.4

Circuit Diagrams

A practical way to describe a circuit is to draw a circuit diagram

Uses standard symbols to represent the components and their connections

SYMBOL COMPONENT

SYMBOL COMPONENT

Connecting wire

Cell

Switch Battery

SYMBOL COMPONENT

SYMBOL COMPONENT

Resistor Voltmeter

Bulb Ammeter

You Try!

Draw a simple circuit (using symbols) that includes: 2 cells A switch A resistor A light bulb

What’s happening here?

Types of Circuits

There are essentially 2 types of circuits: Series Parallel

Series Circuits

Only 1 pathway for current to flow Simple

Electrons only have one path to follow Each electron must go

through each load, in turn

Current (I) is the same at each point in the circuit

Parallel Circuits

More than 1 pathway for current to flow Charges flow around 2 or more

different “loops”

Current is not the same at all points Some electrons will take one path and

others will take a different path

Most circuits are a combination of series and parallel

Ammeters

Ammeter measures current (in amperes, A) at a particular location in the circuit Where the ammeter is located!

Ammeter is always connected in series

Voltmeters

Voltmeter measures potential difference (in volts, V) between 2 points

Electric potential on one side of a load, such as a bulb or resistor, is greater than the electric potential on the other side

Voltmeter measures this difference

Always connected in parallel

Back to this guy…

What if one of the bulbs was burnt out? Bulbs must be connected

in parallel How do we turn the

lights on? 1 switch Power source and switch

must be connected in series

Loads in Series – Current (I) The current is the same at all points in a

series circuit

IT = I1 = I2 = I3…

Loads in Series – Potential Difference (V)

Loads transform electrical energy into other forms of energy

The total energy transformed must equal the work that is done by the cell (power source)

.: The potential difference of the cell must equal the sum of the potential differences of each load

Loads in Series – Potential Difference (V)

VT = V1 + V2 + V3 …

Loads in Series – Resistance (R)

The total resistance of the circuit will increase as more loads are added in series

RT = R1 + R2 + R3 …

What would happen if we added more loads (i.e. light bulbs) in series?

Loads in Parallel – Current (I)

There is more than one path for electrons to flow

The current entering a parallel connection divides

The sum of the currents through each path equals the total current

IT = I1 + I2 + I3 …

Loads in Parallel – Potential Difference (V)

Voltage is the same across all loads in the circuit

Equivalent to the potential difference across the cell

VT = V1 = V2 = V3…

Loads in Parallel – Resistance (R) The total resistance of

loads connected in parallel, is less than the resistance of any of the loads individually

RT < R1; RT < R2; RT <

R3; …