Series and Parallel Circuits

Simple electrical circuits can be made using an energy source and resistors. We can measure current intensity using an ammeter.

Potential difference is measured using a voltmeter.

Symbols used in circuit diagrams:Resistor: Switch: Power source (battery):Ammeter:Voltmeter:

There are two main types of electrical circuits. The way the elements are connected to one another determines the type of circuit.

If the elements (power source and resistors) are connected in one loop (one path) this is called a series circuit.

If the elements are connected to one another using multiple branches (more than one path) then this is called a parallel circuit.

Ammeters and Voltmeters

When measuring the current intensity, the ammeter is always attached in series to the rest of the circuit.

The voltmeter is attached in parallel.

Kirchhoff’s Laws (EST)

Series circuit:When resistors are connected in series all

current travels through each resistor.The disadvantage of such a circuit is the fact that

if one of the appliance burns out, the current flow is broken, as a result the circuit is broken.

The equivalent Resistance: RT = R1 + R2 + R3

The disadvantage is that the total resistance increases as you add on resistors

Total Voltage: VT = V1 + V2 + V3

The voltage drops as you add resistors.

The current: IT = I1 = I2 = I3

The current is the same at every point in the circuit

Parallel Circuit A parallel circuit is when the elements (resistors, light

bulbs, fan, etc.) are connected side by side to each other.

This connection allows the current to flow along different paths at the same time.

The current intensity through any path will be a fraction of the total current.

The advantage of such circuit is that if one resistor burns out there is still current flowing through the rest.

The equivalent Resistance:The equivalent resistance is smaller than the resistance value of

any individual resistor.

RT = (1/R1 + 1/R2 + 1/R3 )-1

Total Voltage

All devices in parallel experience the same potential difference (voltage)

VT = V1 = V2 = V3 The current

The current from the battery equals the sum of the current intensities through each the resistors.

IT = I1 + I2 + I3 ……