Series and Parallel Circuits

Types of Circuit

There are two types of electrical circuits;

SERIES CIRCUITSPARALLEL CIRCUITS

The components are connected end-to-end, one after the other.

They make a simple loop for the current to flow round.

SERIES CIRCUITS

If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITS

The current has a choice of routes.

The components are connected side by side.

If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.

Measuring Current

Electric current is measured in amps (A)

using an ammeter connected in series in the

circuit.

A

Measuring Current

AA

This is how we draw an ammeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

Measuring Current

SERIES CIRCUIT

PARALLEL CIRCUIT

• current is the same at all points in the circuit.

2A 2A

2A

• current is shared

between the

components

2A2A

1A

1A

Measuring Voltage

The ‘electrical push’ which the cell gives to the

current is called the voltage. It is measured in

volts (V) on a voltmeter

V

Different cells produce different voltages. The

bigger the voltage supplied by the cell, the bigger

the current.

Measuring Voltage

Unlike an ammeter a voltmeter is connected

across the components

Scientist usually use the term Potential

Difference (pd) when they talk about voltage.

Measuring Voltage

V

This is how we draw a voltmeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

V

Series Circuit

1.5V

• Voltage is shared between the components

1.5V

3V

• Voltage is the same in all parts of the circuit.

3V

Parallel Circuit

3V

3V

Resistors in Series

When two or more resistors are connected end-to-end, they are said to be in series

The current is the same in all resistors because any charge that flows through one resistor flows through the other

The sum of the potential differences across the resistors is equal to the total potential difference across the combination

Resistors in Series, cont

Potentials add ΔV = IR1 + IR2 = I

(R1+R2)

Consequence of Conservation of Energy

The equivalent resistance has the effect on the circuit as the original combination of resistors

Equivalent Resistance –Series

Req = R1 + R2 + R3 + …

The equivalent resistance of a series combination of resistors is the algebraic sum of the individual resistances and is always greater than any of the individual resistors

Equivalent Resistance –Series: An Example

Four resistors are replaced with their equivalent resistance

Resistors in Parallel

The potential difference across each resistor is the same because each is connected directly across the battery terminals

The current, I, that enters a point must be equal to the total current leaving that point I = I1 + I2

The currents are generally not the same

Consequence of Conservation of Charge

Equivalent Resistance –Parallel, Example

Equivalent resistance replaces the two original resistances

Household circuits are wired so the electrical devices are connected in parallel Circuit breakers may be used in series with other

circuit elements for safety purposes

Equivalent Resistance –Parallel

Equivalent Resistance

The inverse of the equivalent resistance of two or more resistors connected in parallel is the algebraic sum of the inverses of the individual resistance The equivalent is always

less than the smallest resistor in the group

321eq R

1

R

1

R

1

R

1

Equivalent Resistance –Complex Circuit

Ground Wire

Electrical equipment manufacturers use electrical cords that have a third wire, called a case ground

Prevents shocks

Ground Fault Interrupts (GFI)

Special power outlets

Used in hazardous areas

Designed to protect people from electrical shock

Senses currents (of about 5 mA or greater) leaking to ground

Shuts off the current when above this level

Equivalent Resistance Series Circuits

Req = R1 + R2 + R3 + …

Equivalent Resistance Parallel Circuits

321eq R

1

R

1

R

1

R

1