Electromotive Force (EMF)

Definition

Electromotive force (EMF) is the voltage or potential difference generated by an electrical source, such as a battery or generator, that drives the flow of electric current in a circuit. It is the force that causes electrons to move through a conductor, creating an electric current.

5 Must Know Facts For Your Next Test

1. EMF is the driving force that causes electric current to flow in a circuit, overcoming resistance and other opposing forces.
2. EMF is measured in volts (V) and is the potential difference between the positive and negative terminals of a power source.
3. EMF is not the same as voltage, as voltage is the potential difference between two points in a circuit, while EMF is the potential difference generated by the power source.
4. Faraday's Law of Electromagnetic Induction states that a changing magnetic field induces an EMF in a conductor, which is the basis for the operation of generators and transformers.
5. The EMF generated by a power source is determined by the chemical or physical processes within the source, such as the reactions in a battery or the rotation of a generator's armature.

Review Questions

• Explain the relationship between EMF and electric current in a circuit.
  • The EMF generated by a power source is the driving force that causes electric current to flow through a circuit. The current is directly proportional to the EMF and inversely proportional to the resistance in the circuit, as described by Ohm's law: $I = \frac{\varepsilon}{R}$, where $I$ is the current, $\varepsilon$ is the EMF, and $R$ is the resistance. The EMF overcomes the resistance and other opposing forces, allowing the electrons to move and create an electric current.
• Describe the role of Faraday's Law of Electromagnetic Induction in the context of EMF.
  • Faraday's Law of Electromagnetic Induction states that a changing magnetic field induces an EMF in a conductor. This principle is the basis for the operation of generators and transformers, where a changing magnetic field is used to induce an EMF in a conductor, which in turn drives the flow of electric current. In the context of Stokes' Theorem, Faraday's Law can be used to relate the line integral of the electric field around a closed path to the surface integral of the changing magnetic field over the surface bounded by that path.
• Analyze how the EMF generated by a power source is determined by the underlying chemical or physical processes within the source.
  • The EMF generated by a power source, such as a battery or a generator, is determined by the specific chemical or physical processes occurring within the source. In a battery, the EMF is generated by the electrochemical reactions between the anode and cathode materials, which create a potential difference. In a generator, the EMF is generated by the rotation of the armature within a magnetic field, as described by Faraday's Law. The magnitude of the EMF is dependent on factors such as the materials used, the strength of the magnetic field, and the speed of rotation, among other variables. Understanding the underlying principles that govern the generation of EMF is crucial for designing and analyzing electrical systems.

Related terms

Voltage: The potential difference or electrostatic potential between two points in an electrical field, measured in volts.

Electric Current: The flow of electric charge through a conductor, such as a wire, measured in amperes.

Faraday's Law of Electromagnetic Induction: A law that describes the relationship between a changing magnetic field and the electromotive force induced in a conductor.