Understanding Ohm's Law: Resistor Application Explained

Ohm's law is a fundamental principle in electrical and electronic circuits, describing the relationship between voltage, current, and resistance. It states that the current flowing in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance. In other words, if the voltage across a circuit is doubled, the current will also double, but if the resistance is doubled, the current will be halved. This law is named after German physicist Georg Ohm, who, in 1827, published his findings on the relationship between voltage and current. While Ohm's law does not apply to all materials, it is particularly relevant to resistors.

Ohm's Law and resistors

Ohm's Law is one of the most fundamental laws in electrical and electronic circuits, describing the relationship between voltage, current, and resistance. It is named after German physicist Georg Ohm, who, in 1827, published his findings on the relationship between voltage and current in a conductor.

Ohm's Law states that the electrical current through a conductor is proportional to the potential difference across it, and that the electrical resistance of the conductor is constant. This leads to the equation: V = IR, where V is the voltage in volts, I is the current in amperes, and R is the resistance in ohms.

Ohm's Law is particularly important when it comes to understanding electric circuits. It allows us to control the amount of current in a circuit by adding or removing resistors. It can also be used to describe electrical power, as power is equal to the product of current and voltage.

Resistors are passive elements that introduce resistance to the flow of electric current in a circuit. A resistor that functions according to Ohm's Law is called an Ohmic resistor. When current passes through an Ohmic resistor, the voltage drop across the terminals is proportional to the magnitude of the resistance.

Ohm's Law is valid for circuits with multiple resistors that can be connected in series, parallel, or both. It can also be used for circuits with varying voltage or current, making it applicable to alternating current (AC) circuits. However, it cannot be used for capacitors and inductors, as their I-V curves are inherently non-linear.

Ohm's Law can be used to calculate the value of resistors required in circuits, as well as to determine the current flowing in a circuit when the voltage can be easily measured across a known resistor. It is a fundamental tool in electronic circuit design and electrical engineering.

Ohmic and non-ohmic resistors

Ohmic resistors

Ohmic resistors follow Ohm's law, meaning that the current through the resistor is directly proportional to the voltage applied. In other words, if the voltage across the resistor is increased, a graph of voltage versus current will show a straight line (indicating a constant resistance). The slope of the line is the value of the resistance. Ohmic resistors have a constant resistance, regardless of the voltage or current. Examples of ohmic resistors include metals, resistors, nichrome wires, and connecting wires.

Non-ohmic resistors

Non-ohmic resistors do not follow Ohm's law and exhibit a non-linear relationship between current and voltage. The resistance of non-ohmic resistors changes depending on the voltage or current. For example, if the voltage across a non-ohmic resistor is continuously increased, but the currents don’t increase beyond a particular value, it is said to be non-ohmic. A light bulb is a perfect example of a non-ohmic resistor. As the filament in the bulb heats up, the resistance of the bulb increases, which means the graph of voltage versus current becomes a curve rather than a straight line, and Ohm's law doesn't apply. Other examples of non-ohmic resistors include diodes, semiconductors, electrolytes, thyristors, transistors, and filament lamps.

How to calculate resistance, current, and voltage

Ohm's law is a fundamental principle in electrical engineering and physics that describes the relationship between voltage, current, and resistance in an electrical circuit. It was discovered by German physicist Georg Ohm in 1827. The law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them.

The formula for Ohm's law is:

E = I x R

Where:

• E = voltage (measured in volts)
• I = current (measured in amps)
• R = resistance (measured in ohms)

This formula can be rearranged to solve for any of the three variables, as long as you have values for the other two. For example, to find the current (I) when you know the voltage (E) and resistance (R), you would use the formula:

I = E / R

Ohm's law can be used to calculate the voltage, current, or resistance in a circuit, as long as you have values for at least two of these variables. It is important to note that Ohm's law only applies to ohmic materials or components, which exhibit a linear relationship between voltage and current. Nonohmic materials or components do not follow Ohm's law and have a more complex relationship between voltage and current.

Calculating Resistance:

Let's say you have a circuit with a 9-volt battery and a current of 3.00 mA (0.003 amps). To calculate the resistance, you can use the formula:

R = E / I

R = 9 V / 0.003 A

R = 3000 ohms

Calculating Current:

Now, let's calculate the current in a circuit with a voltage of 12 volts and a resistance of 24 ohms. We can use the formula:

I = E / R

I = 12 V / 24 ohms

I = 0.5 A

Calculating Voltage:

Finally, let's find the voltage in a circuit with a current of 2 amps and a resistance of 5 ohms. We can use the original Ohm's law formula:

E = I x R

E = 2 A x 5 ohms

E = 10 volts

These are just a few examples of how to use Ohm's law to calculate resistance, current, and voltage. By understanding this law and its applications, you can gain valuable insights into the workings of electrical circuits and make informed decisions about resistor selection and circuit design.

The importance of Ohm's Law

Ohm's Law is a fundamental principle in electrical engineering and physics that plays a critical role in understanding the relationship between resistance, voltage, and current in electrical circuits. This relationship was first described by German physicist Georg Ohm in 1827, and it holds for most materials and conductors.

Ohm's Law is important because it allows us to mathematically describe and predict the behaviour of electrical circuits. It relates the voltage to the current, with the resistance value moderating the relationship between the two. This means that we can use Ohm's Law to control the amount of current in a circuit by adding or removing resistors.

The law is also important for safety reasons. By calculating the expected current flow and voltage drop in a circuit, engineers can design systems that are safe and reliable. If the voltage applied to a circuit is too high, it can cause the current to increase beyond the capacity of the conductors and components, leading to overheating, damage, and even fires.

Additionally, Ohm's Law is useful for troubleshooting and diagnosing problems in electrical systems. If a test instrument detects abnormal current measurements, it could indicate a supply or circuit issue. By using Ohm's Law, technicians can determine which part of a circuit is faltering and locate the problem.

Ohm's Law is also important for physics students as it allows them to analyse circuit diagrams, especially when combined with Kirchhoff's laws. It provides a foundation for understanding the core rules underpinning most modern technology.

Limitations of Ohm's Law

Ohm's law is a cornerstone of physics, but it has its limitations. It is not a fundamental law of nature like Newton's laws or the laws of thermodynamics. Instead, it is an empirical law, meaning it is an experimentally observed phenomenon. This means it is not universally applicable.

Firstly, Ohm's law is only valid for metal conductors, and even then, physical conditions must remain constant. If the temperature changes, for example, the law may not apply. This is because Ohm's law assumes a linear relationship between voltage and current, but in reality, this is often not the case. A lightbulb is a good example of this. As the filament in a lightbulb heats up, its resistance increases, and the graph of voltage against current becomes a curve rather than a straight line, meaning Ohm's law doesn't apply.

Secondly, Ohm's law is not applicable to gaseous conductors or semiconductors. Materials such as silicon and germanium are non-ohmic conductors and do not obey Ohm's law.

Ohm's law also does not apply to unilateral electrical components such as diodes and transistors, which only permit current to flow in one direction.

Finally, Ohm's law assumes a constant voltage level with respect to time, which is not the case for non-linear electrical components with properties such as capacitance and resistance.

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