The interconnection of various
Electrical Circuit Elements
in a prescribed manner to form a closed path is called an electric
circuit. The system in which electric current can flow from source to
load through one path and after delivering energy at load the current
can return to the other terminal of source through another path is
referred as electric circuit. The main parts of an ideal electric
circuit are
- Electrical Sources (for delivering electricity to the circuit and these are mainly electric generators and batteries)
- Controlling Devices (for controlling electricity and these are mainly switches, circuit breakers, MCBs, and Potentiometer like devices etc.)
- Protection Devices (for protecting the circuit from abnormal conditions and these are mainly electric fuses, MCBs, Switchgear systems).
- Conducting Path (to carry current one point to other in the circuit and these are mainly wires or conductors)
- Load
Thus Voltage and Current are the two basic features of an
Electric Element.
Various techniques by which voltage and current across any element in
any electric circuit are determined is called Electric Circuit Analysis.
In this figure shows a simple
Electric Circuit Containing
- A battery of 30 V
- A carbon resistor of 5kΩ
Due to this a current I flows in circuit and a potential drop of V volts across resistor.
Basic Properties of Electric Circuits
- A circuit is always a closed path.
- A circuit always contain an energy source which acts as source of electrons.
- The electric elements include uncontrolled and controlled source of energy, resistors, capacitors, inductors, etc.
- In an electric circuit flow of electrons takes place from negative terminal to positive terminal.
- Direction of flow of conventional current is from positive to negative terminal.
- Flow of current leads to potential drop across the various elements.
Types of Electric Circuit
The electric circuit can be categorized in three different ways
- Open circuit
- Closed circuit
- Short circuit
Open Circuit
If due to disconnection of any part of an electric circuit if there is no flow of current the circuit is said to be open circuited.
Closed Circuit
If there is no discontinuity in the circuit and current can flow from one part to another part of the circuit then the circuit is said to be closed circuit.
Short Circuit
If two or more phases, one or more phases and earth or neutral of AC system or positive and negative wires or positive or negative wires and earth of DC system touch together directly or connected together by a zero impedance path then the circuit is said to be short circuited.
Electric circuits can further be categorised according to their structural features.
- Series Circuit
- Parallel Circuit
- Series Parallel Circuit.
Series Circuit
When all elements of a circuit are connected one after another in tail to head fashion and due to which there will be only one path of flowing current then the circuit is called series circuit. The circuit elements are said to be series connected. In series electrical circuit same current flows through all element connected in series.
Parallel Circuit
If components are connected in such a way that the voltage drop across each component is same is known as parallel circuit. In parallel circuit the voltage drop across each component is same but the current flowing through each component is different. The total current is the sum of currents flowing through each element.
An example of a parallel circuit is the wiring system of a house. If one of the lights burns out, current can still flow through the rest of the lights and appliances.
In a parallel circuit the voltage is the same for all elements.
When the resistors are connected in parallel:-
To find the total resistance of all components, add the reciprocals of the resistances of each component and take the reciprocal of the sum.
When the inductors are connected in parallel:-
Total inductance of non-coupled inductors in parallel is equal to the reciprocal of the sum of the reciprocals of their individual inductances.
When the capacitors are connected in parallel:-
The capacitors connected in parallel acts as series combination. The total capacitance of capacitors in parallel is equal to the sum of their individual capacitances.
Types of Electric Circuit Elements
Passive Element
The element which receives energy (or absorbs energy) and the either converts it into heat or stored it in an electric or magnetic field called Passive Element.
Example: Resistor, Inductor, Capacitor etc.
Active Element
The elements which supply energy to the circuit is called Active Element.
Examples: Include Voltage and Current sources, Generators etc.
Note: A transistor is an active circuit element, meaning that it can amplify the power of a signal. On the other hand, Transformer is not an active element because it does not amplify the power and power remains same both in primary sides and secondary sides. Transformer is an example of passive element.
Bilateral Element
Conduction of current in both directions in an element with same magnitude is termed as Bilateral Element.
Example: Resistor, Inductor, Capacitor etc. This figure shows a bilateral element can conduct from both sides and offers same resistance for current from either side
Unilateral Element
Conduction of current in one direction is termed as Unilateral Element.
Example: Diode, Transistor etc. This figure shows the unilateral element. When diode is forward biased it offers very small resistance and conducts. While when reverse biased it offers very high resistance and don't conduct.
Lumped Elements
When the voltage across and current through the element doesn't vary with dimension of element, it is called Lumped Elements.
Example: Resistor connected in any electrical circuit.
Distributed Element
When the voltage across and current through the element changes with dimension of element, it is called Distributed Element.
Example: Resistance of the transmission line.
Electrical Circuit Symbol
Electrical circuit contains a symbol for every component and product. A circuit diagram uses symbols to represent parts of circuit. Now a day’s electrical circuit is design and managing by using different software like ORCAD, CAD, MATLAB, SCADA. If you want to read any circuit you should familiar with the entire
Electrical Symbol.
| Component Group | Component | Symbol |
| Sources | Cell |  |
| Battery |  |
| DC Power Supply | |
| Variable DC Power Supply |  |
| AC Power Supply |  |
| Resistors | Resistor |  |
| Variable Resistor |  |
| Potentiometer, Voltage Divider |  |
| Light Dependent Resistor (LDR) |  |
| Filament Globe |  |
| Thermistor |  |
| Fuse |  |
| Capacitors | (Non-Polarised) Capacitor |  |
| Variable Capacitor |  |
| Polarised Capacitor, Electrolytic Capacitor |  |
| Transformers | Iron-cored Transformer
(one Secondary Winding) |  |
| Iron-cored Transformer
(one Secondary Winding – centre-tapped) |  |
| Iron-cored Transformer
(two Secondary Windings) |  |
| Diodes | Junction Diode |  |
| Zener Diode |  |
| Photo Diode |  |
| Light Emitting Diode (LED) |  |
| Diode Bridge |  |
| Transistors | npn transistor |  |
| pnp Transistor |  |
| n-Type Junction Field Effect Transistor (NJFET) |  |
| p-Type Junction Field Effect Transistor (PJFET) |  |
| Integrated Circuits | Integrated Circuit (IC) |  |
| Switches | Single Pole, Single Throw (SPST) Switch |  |
| Single Pole, Double Throw (SPDT) Switch |  |
| Double Pole, Single Throw (DPST) Switch |  |
| Double Pole, Double Throw (DPDT) Switch |  |
| Normally Open (NO) Switch |  |
| Normally Closed (NC) Switch |  |
| Relay |  |
| Meters | Ammeter |  |
| Voltmeter |  |
| Galvanometer |  |
| Cathode Ray Oscilloscope (CRO) |  |
| Amplifiers | Voltage Amplifier |  |
| Operational Amplifier (Op Amp) |  |
| Transducers | Motor |  |
| Microphone |  |
| Loudspeaker |  |
| Logic Gates | NOT or Invert Gate |  |
| OR Gate |  |
| XOR (Exclusive OR) Gate |  |
| NOR Gate |  |
| AND Gate |  |
| NAND Gate |  |
| External Connections | Earth |  |
| Aerial |  |
| Circuit Connections | Non - Connected Leads |  |
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