What is an Electric circuit?

What is an electrical circuit?

 An electrical circuit can be defined as a way or path or line through which an electrical current flows. The path may be closed (joined at both ends), making it a loop, called closed electric circuit. A closed circuit makes electrical current flow possible. It can also be an open circuit where the electron flow is cut short because the path is not complete or broken. An open circuit does not allow electrical current to flow.

Electric Circuit
Electric Circuit

Following are the basic set of symbols that you may find on circuit diagrams.

Electrical Circuit Symbols:
Electrical Circuit Symbols:
Electrical Circuit Symbols:

It is very important to know the basic parts of a simple circuit and the symbols that relate to them. A simple circuit has conductors, a switch, a load and a power source.

Here are the functions of each part:
  • Conductors:
These are usually called wires and consists of copper wires with no insulation. They make the way or path through which the electricity flows. One piece of the wire connects the current from the power source (cell) to the load/resistance. The other piece connects the load back to the power source.
  • Switch:
The switch is simply a small device that allows you to close or open the circuit. When the switch is closed, the circuit is closed and electricity flows and when switch is open the circuit is open and the current does not flow.

  • The Load/Resistance:
The load is a small light bulb or buzzer that lights when the circuit is turned on. The load is also known as a resistor.

  • Cell:
Cell is the source of power to the circuit. (Note that more than one cell put together is known as a battery)

The diagram below shows how a basic circuit looks like.

Diagram of a basic electrical circuit:

Diagram of a basic electrical circuit:
Diagram of a basic electrical circuit:

Note: It is important to draw circuits with clean straight lines, as shown in diagram B. Avoid realistic sketches. It is important to know that a circuit can have more than the basic components in the diagram. It can have multiple batteries or bulbs or any other components.

Types of an Electric circuits

  •  Series circuits
A series circuit is one that has more than one resistor (or you can say load i.e. bulbs, buzzer etc.), but only one path through which the electricity (current) flows. From one end of the cell (battery), the electrons flow along one path with NO branches (or split), through the resistors, to the other end of the cell. All the components in a series circuit are connected end-to-end.
A resistor in a circuit can be defined as anything that uses some of the power from the cell. In the following examples, the resistors are the bulbs (in other examples it may be buzzer, heater etc). In a series circuit, the components are arranged in a line, one after the other.

The simple series circuit can be drawn as following:

series circuit
series circuit

The disadvantage of series electric circuit is that each time when there is damage (break) in any one of the resistors the entire circuit will not function. For example, if one light bulb goes out, all the other lights will go off because the path to flow current is broken and the circuit is cut off (i.e circuit is open)

One advantage of this type of circuit is that you will always know if there is a break in a series circuit.

If there are many bulbs in a circuit with a battery (cell), it is very likely that the light will be dimmer because many resistors are acting on the same voltage of power from the battery.
  • Parallel circuits
In a parallel circuit, there is more than one resistor (bulb) and they are arranged on many paths. This means electricity (electrons) can travel from one end of the cell through more than one branches to the other end of the cell.
Following is an electric circuit illustrating the resistors in parallel circuit:
parallel circuit:
parallel circuit:

You will notice from the above that there is more than one path:

PATH 1: A-B-C-D-E-F and back to A.
PATH 2: A-B-C-G-H-D-E-F and back to A.
From the above, it is clear that electricity from the cell can take either path A or Path B to return to the cell. The great advantage about parallel circuits over the series circuit is that, even when one resistor (bulb) burns out, the other bulbs will work because the electricity is not flowing through only one path instead it is flowing through multiple path.
Bonus point: Think of all the light bulbs in your home. If one bulb burns out, the other bulbs in the rooms still work.
Another great thing is that the bulbs in a parallel circuit do not dim out like the case in series circuits. This is because the voltage across one branch is the same as the voltage across all other branches.

What is a short circuit?

A simple, well-designed circuit, as discussed earlier, has a cell providing current along a path (wire), to a load (resistor) and from load back to the other end of the cell as shown in the figure below.
simple, well-designed circuit
simple, well-designed circuit
As the voltage gets to the resistor (load), there is a power drop, because the resistor uses some of the electricity up to produce heat and light. This means that the voltage that ends up at the other side of the cell is reduced.

short circuit
short circuit
In case of short circuit, there is absence of  load. For many reasons, the wires in a circuit can find a short-cut, bypassing the load (and other components). This causes the same voltage from the cell to flow to the other end of the cell. When short circuit the high voltage causes the wires to heat up and eventually may catch fire.
Here are a few reasons for short circuit:
  1. Wires may lose their insulation and touch each other in the circuit
  2. There could be a fault (improper wiring) in a device
  3. Intentionally connecting both ends of a cell / battery with wires. This causes a massive drain of electricity and the battery loses its power in a very short time.
A short circuit can cause heating, melting of wires, harmful smoke and smell, and blinding light. In some cases we use short circuit to complete our tasks like what you see during welding.

Electric Circuit protection:

It is very important that electrical devices in homes, cars, offices, schools, airplanes, buses and other complex machines are protected from higher voltage than the wires are designed to take — otherwise, the devices can break (i.e. the short circuit may take place) and even may catch fire.

In real life applications in an electrical circuits, it is possible that wires (conductors) lose their insulation and come into contact with the ground or other conductors (i.e. short circuit). If that happens, the voltage in the wire will have no resistor (load) and the same high voltage will be returned to the source of power.
This can result in overheating, as there is way too much voltage than the wires can take. Overheating will then cause melting and eventually a break (open) in the circuit and even in some worst cases it may lead to fire.
One way of circuit protection is by adding a fuse, circuit breaker or thermal breaker to the circuit.

These work in similar ways, but let us discuss in detail about a fuse:

A Fuse:

A fuse is nothing but simply a strip of alloy wire (made of bismuth and tin), which is connected to the circuit. The fuse is usually designed to tackle specific range of electricity (current). For example is a 3amp fuse is fixed into a circuit — it cannot take any more than 3amps of electricity. If for any reason, there is a surge or increase in the current in the circuit, the fuse will melt immediately and break. This will stop the flow of high voltage and prevent any potential damage to the circuit or device and hence to the life and property of human.

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