Electric Circuit

Electric Circuit – Definition & Basics

An electric circuit is a closed path through which electric current flows, allowing energy to be transferred between electrical components. In such a circuit, electrons move through the loop under the influence of an electric field produced by a source such as a battery or generator.

Key Features of an Electric Circuit

• An electric circuit must form a complete, closed path for current to flow.
• Electric current is the flow of electrons through the circuit path.
• The circuit energy is supplied by a source that establishes an electric field.

Common Circuit Components

Resistors:

oppose the flow of electric current and dissipate electrical energy in the form of heat.

Capacitors:

store electrical energy in the form of an electric field between two plates.

Inductors:

store energy in a magnetic field when current flows through them.

Semiconductor Devices:

such as LEDs and transistors are used to control and regulate current flow.

Integrated Circuits:

contain multiple electronic components combined into a single compact unit.

How an Electric Circuit Works

In a closed electric circuit, electrons move from the source, through the circuit elements, and return to the source. The source provides energy, while the circuit elements convert this energy into useful forms such as heat, light, or motion.

Types of Electric Circuits

Series Circuits:

components are connected end to end, and the same current flows through all elements.

Parallel Circuits:

components are connected across the same voltage source, allowing multiple current paths.

Series-Parallel Circuits:

combine both series and parallel connections to achieve desired electrical characteristics.

Modeling a Simple Electric Circuit

Suppose we want to construct a circuit model for a flashlight. What are the important components?

• Batteries: $v_s$
• Filament (lamp): $R_L$
• Case: $R_c$
• Switch
• Coil: $R_1$

We can model the batteries with a voltage source. The other components can be modeled with resistors, except for the switch. The switch is nothing more than a connection that can be either open (off) or closed (on). The filament is more than a resistor: it gives off light and heat. However, we are interested in only electrical behavior, so we will ignore those properties and stick with the resistor as a model. How do we connect these elements together? An examination of a flashlight shows that these things are connected in series (more on that later), which is to say they are connected end-to-end. The following diagram results. This is a circuit model for a flashlight. We have made some assumptions here

• The switch is ideal and has no resistance when it is closed, and an infinite resistance when it is open. Real switches have some small resistance when closed, and a large but finite resistance when open.
• The batteries are ideal: the voltage does not depend on the fact that current is flowing through them, which is not the case for real batteries.
• We use a resistor, which has constant R, to model the lamp. In fact, the resistance of a real flashlight lamp changes a little when current flows through it. We will ignore that detail here.

Now what? We want to solve this circuit. That means we want to know all the voltages and currents associated with all the circuit elements. To do that, we need to know something more about the voltages and currents in this circuit. That information comes from Kirchhoff's Laws.

Conclusion

An electric circuit is a fundamental concept in electrical engineering, defined as a closed path that allows electric current to flow. Understanding circuit components, structure, and operation is essential for designing efficient and reliable electrical systems.