Electrical potential is a fundamental concept in physics that describes the potential for an electric charge to move or perform work within an electric field. It measures the energy stored per unit of electric charge at a specific point in space. This concept is often compared to gravitational potential energy.
When a stone is lifted against gravity, the work done is stored as potential energy. Similarly, electrical potential is the work required to move a positive test charge against an electric field from a reference point to a specific location. It represents the “electrical pressure” at that location, indicating the energy available for release.
The Core Concept: Potential Energy per Unit Charge
We must distinguish between Electrical Potential Energy and Electrical Potential. Electrical Potential Energy is the total stored energy of a charged particle within an electric field, measured in Joules. This value depends on the particle’s location and the magnitude of the charge. For example, a particle with twice the charge will possess twice the potential energy at the same location.
Electrical Potential, represented by \(V\), is a property of the space itself and is independent of any charge placed there. It is defined as the electrical potential energy per unit of charge. Because it is a ratio of energy to charge, it is a scalar quantity, meaning it has magnitude but no direction.
This concept requires a defined reference point where the potential is considered zero. For theoretical calculations, this zero-potential reference is often taken to be infinitely far away from the charge. In practical applications, this reference is typically a physical ground or a common neutral point within a circuit.
Measuring Potential: Defining the Volt and Potential Difference
Measuring the absolute electrical potential at a single point is less practical than measuring the Potential Difference between two points. This difference is known as voltage and is the driving force behind all electrical circuits. Voltage quantifies the work per unit charge required to move a charge from one point to the other.
The unit of measurement for both electrical potential and potential difference is the Volt (\(V\)). One Volt is defined as one Joule of energy per one Coulomb of electric charge (\(1 V = 1 J/C\)). This definition links the concept of potential to the units of energy (Joule) and charge (Coulomb).
When measuring voltage across a battery or wall outlet, we are measuring the difference in electrical potential between the two terminals. Establishing a common reference point, such as connecting one terminal of the voltmeter to a designated “ground” or zero-potential wire, is essential for a meaningful measurement. This zero reference allows all other potentials in the system to be measured relative to a fixed baseline.
Potential in Action: Driving Current and Electric Fields
The existence of a potential difference drives the movement of electric charge, which is called current. Positive charges naturally move from a region of higher electrical potential to a lower one, similar to a ball rolling down a hill. This movement converts stored electrical potential energy into kinetic energy or work.
The electric field is the rate at which the potential changes over distance. A high electric field strength indicates a steep change in potential. Charges experience a force from the electric field that always acts in the direction that decreases their electrical potential energy.
In a uniform electric field, the potential decreases linearly in the direction of the field. When current flows through a conductor, the potential difference does work on the charges, propelling them and powering devices. The potential energy lost by the moving charges is transformed into other forms of energy, such as light, heat, or mechanical work.
Applications of Electrical Potential
Electrical potential is the fundamental mechanism allowing energy to be stored and utilized. Batteries are chemical systems designed to create and maintain a consistent potential difference between their terminals. This sustained voltage allows stored chemical energy to be converted into electrical work.
Household electricity operates by maintaining a large potential difference, typically 120 V or 240 V, between the active wire and the neutral or ground wire. This voltage ensures enough energy is available per unit of charge to power appliances. Electrical potential also plays a role in biological processes within the human body.
The function of nerve cells, or neurons, depends on maintaining a potential difference known as the membrane potential across the cell wall. Changes in this potential are how neurons transmit signals. The ability to create and control electrical potential is essential to both modern technology and biology.