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Electric circuit

An electric circuit is a closed path (with no breaks or gaps) along which electrical charges (electrons) flow powered by an energy source.

Representing electric circuits

Components of electrical circuits

Some common elements (components) which can be found in electrical circuits include light bulbs, batteries, connecting leads, switches, resistors, voltmeters and ammeters. You will learn more about these items in later sections, but it is important to know what their symbols are and how to represent them in circuit diagrams. Below is a table with the items and their symbols:

Component Symbol Usage
light bulb
glows when charge moves through it
The longer line shows the positive (+) side of the battery, the shorter line shows the (-) side of the battery.
provides energy for charge to move - conventional current flow from positive to negative through a circuit
allows a circuit to be open or closed
resists the flow of charge
measures potential difference
measures current in a circuit
connecting lead
connects circuit elements together

Circuit diagrams

Representing circuits

A physical circuit is the electric circuit you create with real components.

A circuit diagram is a drawing which uses symbols to represent the different components in the physical circuit.

We use circuit diagrams to represent circuits because they are much simpler and more general than drawing the physical circuit because they only show the workings of the electrical components. You can see this in the two pictures below. The first picture shows the physical circuit for an electric torch. You can see the light bulb, the batteries, the switch and the outside plastic casing of the torch. The picture is actually a cross-section of the torch so that we can see inside it.

Physical components of an electric torch. The dotted line shows the path of the electrical circuit.

Below is the circuit diagram for the electric torch. Now the light bulb is represented by its symbol, as are the batteries, the switch and the connecting wires. It is not necessary to show the plastic casing of the torch since it has nothing to do with the electric workings of the torch. You can see that the circuit diagram is much simpler than the physical circuit drawing!

Circuit diagram of an electric torch.

Series and parallel circuits

There are two ways to connect electrical components in a circuit: in series or in parallel .

Series circuit

In a series circuit, the charge flowing from the battery can only flow along a single path to return to the battery.

Parallel circuit

In a parallel circuit, the charge flowing from the battery can flow along multiple paths to return to the battery.

The picture below shows a circuit with two resistors connected in series on the left and a circuit with two resistors connected in parallel on the right. In the series circiut, the charge path from the battery goes through every component before returning to the battery. In the parallel circuit, there is more than one path for the charge to flow from the battery through one of the components and back to the battery.

This simulation allows you to experiment with building circuits.

run demo

Draw the circuit diagram for a circuit which has the following components:

  1. 1 battery
  2. 1 lightbulb connected in series
  3. 2 resistors connected in parallel

Draw the circuit diagram for a circuit which has the following components:

  1. 3 batteries in series
  2. 1 lightbulb connected in parallel with 1 resistor
  3. a switch in series with the batteries


  1. Using physical components, set up the physical circuit which is described by the circuit diagram below and then draw the physical circuit:
  2. Using physical components, set up a closed circuit which has one battery and a light bulb in series with a resistor.
    1. Draw the physical circuit.
    2. Draw the resulting circuit diagram.
    3. How do you know that you have built a closed circuit? (What happens to the light bulb?)
    4. If you add one more resistor to your circuit (also in series), what do you notice? (What happens to the light from the light bulb?)
    5. Draw the new circuit diagram which includes the second resistor.
  3. Draw the circuit diagram for the following circuit: 2 batteries and a switch in series, and 1 lightbulb which is in parallel with two resistors.
    1. Now use physical components to set up the circuit.
    2. What happens when you close the switch? What does does this mean about the circuit?
    3. Draw the physical circuit.

Discussion : alternative energy

At the moment, most electric power is produced by burning fossil fuels such as coal and oil. In South Africa, our main source of electric power is coal-burning power stations.(We also have one nuclear power plant called Koeberg in the Western Cape). However, burning fossil fuels releases large amounts of pollution into the earth's atmosphere and contributes to global warming. Also, the earth's fossil fuel reserves (especially oil) are starting to run low. For these reasons, people all across the world are working to find alternative /other sources of energy and on ways to conserve /save energy. Other sources of energy include wind power, solar power (from the sun), and hydro-electric power (from water, e.g. dammed rivers) among others.

With a partner, take out the lists you made earlier of the item/appliances/machines which used electricity in the following environments. For each item, try to think of an alternative AND a way to conserve or save power.

For example, if you had a flourescent light as an item used in the home, then:

  • Alternative: use candles at suppertime to reduce electricity consumption
  • Conservation: turn off lights when not in a room, or during the day.


  • At home
  • At school
  • At the hospital
  • In the city

Once you have finished making your lists, compare with the lists of other people in your class.

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
The fundamental frequency of a sonometer wire streached by a load of relative density 's'are n¹ and n² when the load is in air and completly immersed in water respectively then the lation n²/na is
Mukesh Reply
Properties of longitudinal waves
Sharoon Reply

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Source:  OpenStax, Siyavula textbooks: grade 10 physical science [caps]. OpenStax CNX. Sep 30, 2011 Download for free at http://cnx.org/content/col11305/1.7
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