EMF vs. Terminal Voltage

Attribute	EMF	Terminal Voltage
Definition	The electromotive force (EMF) is the voltage generated by a source such as a battery or generator.	The terminal voltage is the voltage measured across the terminals of a device or circuit.
Symbol	ε or E	Vt
Unit	Volts (V)	Volts (V)
Causes	EMF is caused by chemical reactions, electromagnetic induction, or other means.	Terminal voltage is caused by the flow of current through a resistance, resulting in a voltage drop.
Internal Resistance	EMF does not consider internal resistance.	Terminal voltage takes into account the internal resistance of the source.
Measured	EMF cannot be directly measured.	Terminal voltage can be directly measured using a voltmeter.
Open Circuit	EMF remains constant in an open circuit.	Terminal voltage is equal to EMF in an open circuit.
Loaded Circuit	EMF decreases when a load is connected due to internal resistance.	Terminal voltage decreases further due to the voltage drop across the internal resistance.

Introduction

When studying electrical circuits, two important concepts that often come up are electromotive force (EMF) and terminal voltage. While both terms are related to the flow of electric current, they have distinct attributes and play different roles in circuit analysis. In this article, we will explore the characteristics of EMF and terminal voltage, highlighting their differences and understanding their significance in electrical systems.

EMF: Electromotive Force

Electromotive force, commonly abbreviated as EMF, is a fundamental concept in electrical circuits. It represents the energy per unit charge supplied by a source, such as a battery or a generator, to maintain a potential difference across a circuit. EMF is measured in volts (V) and is responsible for initiating the flow of electric current.

One of the key attributes of EMF is that it represents the maximum potential difference across a circuit when no current is flowing. It is the driving force that pushes charges through the circuit, overcoming any resistance encountered. EMF is independent of the circuit's internal resistance and is solely determined by the source itself.

Another important aspect of EMF is that it is always constant for a given source, regardless of the circuit's characteristics. Whether the circuit is open or closed, series or parallel, the EMF remains the same. This attribute allows us to calculate the total potential difference in a circuit by summing the individual EMFs of the sources present.

Furthermore, EMF is not affected by the presence of any external loads or components. It represents the ideal voltage provided by the source, assuming no energy losses within the circuit. However, in real-world scenarios, factors like internal resistance and other losses can reduce the actual voltage delivered to the circuit, leading us to the concept of terminal voltage.

Terminal Voltage

Terminal voltage, also known as load voltage or circuit voltage, refers to the actual voltage available at the terminals of a source or across a specific component in a circuit. Unlike EMF, terminal voltage takes into account the internal resistance of the source and any voltage drops across other elements in the circuit.

When current flows through a circuit, the presence of internal resistance causes a voltage drop within the source itself. This voltage drop reduces the potential difference available to the external circuit, resulting in a lower terminal voltage compared to the EMF. Terminal voltage can be calculated using Ohm's Law, which states that V = EMF - IR, where V is the terminal voltage, EMF is the electromotive force, I is the current flowing through the circuit, and R is the internal resistance.

Terminal voltage is influenced by the circuit's characteristics, such as the resistance of the load and the internal resistance of the source. As the load resistance increases, the terminal voltage decreases due to a larger voltage drop across the internal resistance. Conversely, a lower load resistance results in a higher terminal voltage as less voltage is lost within the source.

It is important to note that terminal voltage can never exceed the EMF of the source. The maximum terminal voltage occurs when the circuit is open, and no current is flowing, resulting in the full EMF being available across the terminals. As the current increases, the terminal voltage decreases due to the voltage drop across the internal resistance.

Comparison of Attributes

Now that we have explored the individual attributes of EMF and terminal voltage, let's summarize their differences:

• EMF represents the maximum potential difference across a circuit, while terminal voltage is the actual voltage available at the terminals.
• EMF is constant for a given source, regardless of the circuit's characteristics, while terminal voltage depends on the circuit's resistance and the internal resistance of the source.
• EMF is independent of the presence of external loads or components, while terminal voltage is affected by the circuit's characteristics and the current flowing through it.
• Terminal voltage can never exceed the EMF of the source, as it takes into account the voltage drop across the internal resistance.

Conclusion

EMF and terminal voltage are both important concepts in electrical circuits, representing different aspects of the voltage present in a circuit. EMF acts as the driving force, providing the maximum potential difference, while terminal voltage considers the effects of internal resistance and other circuit elements. Understanding the attributes of EMF and terminal voltage allows us to analyze and design circuits more effectively, taking into account the real-world limitations and characteristics of electrical sources.