Key Points about EMF:

1. Definition: EMF is the energy supplied per unit charge by a source of electric power. It is expressed in volts (V), which is the unit of electrical potential difference or voltage.

2. Not a "Force" in the Classical Sense: Despite the name, electromotive force is not a force in the traditional sense (like a mechanical force). Instead, it refers to the potential difference generated by a source that causes current to flow when connected to a circuit.

3. Units: EMF is measured in volts (V), the same unit used for voltage. The higher the EMF, the greater the ability of the source to push charge through a circuit.

4. Source of EMF:

   • Batteries: In a battery, chemical reactions create an EMF by converting chemical energy into electrical energy.

   • Generators: In a generator, mechanical energy (such as rotational motion) is converted into electrical energy through electromagnetic induction, creating an EMF.

   • Photovoltaic Cells: Solar cells convert light energy into electrical energy, generating EMF through the photoelectric effect.

5. Formula for EMF: In a simple circuit, the EMF (denoted as ε) can be related to the voltage (V) across the terminals of a source:
   EMF(ε)=V+I×r\text{EMF} (\varepsilon) = V + I \times rEMF(ε)=V+I×r
   where:

   • V is the terminal voltage (the voltage across the load),

   • I is the current flowing through the circuit,

   • r is the internal resistance of the source.

6. Internal Resistance: The source of EMF, such as a battery, usually has some internal resistance, which reduces the actual voltage available to the circuit once current begins to flow. This is why the voltage across the battery's terminals can drop when a load is connected.

7. Applications:

   • Batteries: Provide EMF to power electronic devices.

   • Generators: Supply EMF to the electrical grid or mechanical systems.

   • Electric Circuits: EMF is what drives current through circuits, powering motors, lights, and other devices.