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Ohm’s Law Explained: Voltage, Current, and Resistance

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Introduction

Ohm's Law, named after German physicist Georg Simon Ohm, is crucial in understanding electrical behavior in circuits within the realm of electrical engineering. Exploring this fundamental law reveals the mysteries of electrical phenomena for engineers, whether experienced or new to the field. Let's delve into the significance of Ohm's Law in engineering applications together.

Alt text: "Diagram illustrating Ohm’s Law with three triangles showing voltage, current, and resistance. Equations below: V=IR, I=V/R, R=V/I."

Ohm’s Law

The relationship between voltage (V), the current (I) and resistance (R) in a d.c. circuit was first discovered by German scientist George Simon Ohm. This relationship is called Ohm’s law and may be stated as under:
 
The ratio of potential difference (V) between the ends of a conductor to the current (I) flowing between them is constant, provided the physical conditions (e.g. temperature etc.) do not change i.e.
`frac vi`= Constant = R
where R is the resistance of the conductor between the two points considered.For example,if in Fig.1
  1. When the voltage between points A and B is V volts and current is I amperes, the ratio V/I remains constant and equals R, the resistance between A and B. Doubling the voltage also doubles the current, keeping the V/I ratio unchanged. If you plot a graph of voltage V against current I, the result is a straight line passing through the origin, as shown in Fig. 2.
  2. The resistance R between points A and B is given by slope of the graph i.e.
R=tan θ = V/I = Constant

Ohm’s law can be expressed in three forms viz.

 I = V/R ; V = IR ; R = V/I

You can apply these formulae to any part of a DC circuit or to the entire circuit. When you measure voltage in volts and current in amperes, the resulting resistance is expressed in ohms.

                    Circuit diagram showing a resistor labeled "R" between two points, A and B. Current "I" flows from A to B, with voltage "V" across the resistor.
                       Figure 1                        
                                        Coordinate plane diagram with a vector in the first quadrant, forming an angle θ with the positive x-axis. Axes labeled V (vertical) and I (horizontal).

  Figure 2

 

Ohm's Law is a fundamental tool for understanding and forecasting the performance of electrical circuits. It helps engineers establish the connection between voltage, current, and resistance, allowing for the enhancement of different electronic systems.

Non-ohmic Conductors

Non-ohmic conductors, such as vacuum tubes, transistors, and electrolytes, do not follow Ohm’s Law (I ∝ V). They often exhibit one or more nonlinear electrical properties:
  • The V-I graph is non-linear i.e. V/I is variable.
  • The V-I graph may not pass through the origin as in case of an ohmic conductor.
  • A non-ohmic conductor may conduct poorly or stop conducting altogether when you reverse the potential difference.

Engineers generally solve non-linear circuit problems using graphical methods.

                                       Graph showing a junction diode's I-V curve. Positive voltage yields an exponential rise in current; negative voltage shows minimal current flow.
        Figure 1
                                        Graph of neon gas V-I characteristics with voltage on the horizontal axis and current on the vertical. Shows breakdown above a positive voltage.
       Figure 2
                                                 Graph of a diode valve with voltage on the horizontal axis and current on the vertical. The curve shows current increasing rapidly in forward bias.
   Figure 3
Above figure illustrates the graphs of non-ohmic conductors. Note that V-I graphs for these non-ohmic conductors are not a straight line.

Implications and Applications of Ohm's law

The consequences of Ohm's law resound in many branches of electrical engineering, from simple circuit analysis to high-end electronics design.
  1. Circuit Design and Analysis: Ohm’s Law forms the foundation of circuit design, helping engineers calculate voltage, current, and resistance to select components, ensure proper operation, and troubleshoot effectively.
  2. Power Electronics: In power electronics applications like power supply design and motor control, Ohm's Law allows engineers to determine the suitable voltage and current ratings for components like resistors, capacitors and inductors. Using Ohm's Law, engineers assure the effective power delivery and minimal energy losses in electronic platforms.
  3. Electrical Safety: Having a solid understanding of Ohm’s Law is critical, especially when it comes to ensuring electrical safety in various setups such as homes, businesses, and industrial environments. In fact, it serves as the foundation for analyzing and designing safe electrical circuits. Moreover, by applying Ohm’s Law, one can accurately calculate current, voltage, and resistance levels, thereby preventing potential hazards such as overheating, short circuits, or electrical fires. Therefore, this fundamental principle is essential for both professionals and individuals working with electrical systems.Engineers and electricians, using voltage, current, and resistance calculations in electrical circuits, can evaluate potential hazards, implement proper safety measures and prevent electrical incidents.
  4. Instrumentation and Measurement: Ohm's Law is the foundation of many electronic measurement techniques and instruments that include multimeters, oscilloscopes and signal generators. Engineers use Ohm's law for interpreting measurement data, for calibration of instruments, and for verification of electronic device performance.

Conclusion

Ohm's Law is essential in electrical engineering, offering a foundational structure for comprehending the operation of electrical circuits and parts. Engineers rely on the principles of Ohm's Law for tasks ranging from basic circuit analysis to advanced electronics design.

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