DC Circuit Analysis

Circuit and its elements

A Circuit is that encloses conducting path through which an electric current flows. The circuit consists of active and passive elements.

Active elements are those which have their own energy and they transfer energy to passive elements. Examples are voltage and current.

Passive elements are those which do not have their own energy. They receive energy from the active elements. Examples are resistors, capacitors, inductors.

Active and Passive Networks

Active Networks are those which contain one or more passive elements.

Passive Networks are those which does not contain any active elements and it is the combination of only passive elements.

Resistor And Resistance

A resistor is a device that resists the flow of current and Resistance is the property of a substance due to which it opposes the flow of current. It is a dissipative element i.e. it converts electrical energy into heat energy as current flows from through it.

They provide a way to control voltage and currents that’s why they are very common in circuits. Resistors are uses to divide voltage and limit the amount of current. The resistor is denoted by R. The unit of resistance is ohm “Ω”.

A resistance has color stripes on them that represent their value of resistance. Resistor those uses in the circuit have special color coding from which resistivity of the resistor can be determine.


The diode conducts in only in one direction conduction is form anode to cathode.

The diode is said to be forward biased if anode is connected to the positive terminal and cathode to negative and reverse biased if connected vice-versa.

Zener Diode

Zener diode behaves like an ordinary diode if forward biased or reverses biased with small voltage. If Zener diode is reverse biased with a voltage greater than a certain amount called Zener diode, it conducts easily. The voltage of the Zener diode is fixed when a Zener diode is manufactured. Zener diodes are used to regulate the output power supply circuits.


Capacitor consists of two metals plates with a layer of insulator called dielectric. The capacitance of capacitor is measured in farad. Generally there is a mark to show cathode terminal of the capacitor otherwise larger terminal indicates positive and shorter the negative.


Transistors are three-terminal semiconductor devices. Based on composition, they are of PNP type and NPN type. They are used for switching and amplification.

Transistors enclosed in plastic case has flat surface and that metal case has tag on its rim to identify the terminals wires.

IC (Integrated Circuits)

Devices made by the integration of electric components like transistors, diodes, and resistors into a single chip are called Integrated circuits. They may vary in combination and size according to their types and usage. For example, comparators consist of 23 transistors, 2 diodes, and 19 resistors in its one type. Other examples are Audio Amplifier ICs, Timer ICs, Logic ICs, Memory chips, etc. They are used for amplification, multi-switching, and storing data as RAM and ROM, etc.


LED stands for light-emitting diodes. They are used as indicators. Some LEDs are even multicolor use to indicate the different status of voltage and current in circuits. Usually, not always, the cathode wire is shorter than the anode wire. Another way is to look at the rim. The rim is flat on the side nearer to the cathode terminal.


Generally, Inductor is a coil of wire. It often has a core. There are two main types of inductors: Chokes and Tuning Coils. Two or more coils are wrapped on one former to make a transformer. It is also a storage device, but store energy in terms of magnetic field or electric field. Its unit is (H) Henry.

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