Voltage (Potential Difference)
Voltage, or potential difference, is the difference in electric potential between two points in a circuit or electric field, representing the work done per unit positive charge to move it from one point to another against or with the electric force. Measured in volts (V), it is the driving force (electromotive force) that causes electric current to flow through a conductor from higher to lower potential. Voltage is the key parameter in electrical engineering and electronics, governing the operation of batteries, power supplies, electronic components, and all forms of electrical power transmission.
Key Formula
V_AB = V_A − V_B = W_AB / q
LaTeX: V_{AB} = V_A - V_B = \frac{W_{AB}}{q}
| Symbol | Meaning | Unit |
|---|---|---|
| V_AB | Potential difference (voltage) between points A and B | V |
| V_A | Electric potential at point A | V |
| V_B | Electric potential at point B | V |
| W_AB | Work done moving charge q from B to A | J |
| q | Electric charge being moved | C |
Worked Example
Problem
A 9 V battery moves 4 C of charge from the negative terminal to the positive terminal through an external circuit. Calculate the work done by the battery (electrical energy supplied) and the current if this takes 2 seconds.
Solution
Step 1: Calculate work done using potential difference. W = V × q W = 9 V × 4 C = 36 J Step 2: Calculate electric current (charge per unit time). I = q / t = 4 C / 2 s = 2 A Step 3: Verify using power: P = V × I = 9 × 2 = 18 W Energy = P × t = 18 × 2 = 36 J ✓
Answer
Work done = 36 J; Current = 2 A
Typical Voltage Values in Real-World Systems
| Source / Device | Voltage (V) | Type | Application |
|---|---|---|---|
| AA/AAA battery | 1.5 V | DC | Torches, remote controls |
| Car battery | 12 V | DC | Starting engine, lights |
| Household mains (India) | 230 V | AC (50 Hz) | Appliances, lighting |
| High-tension power lines | 11,000–400,000 V | AC | Long-distance transmission |
| Lightning bolt | ~300,000,000 V | DC pulse | Natural discharge |
| USB port (computer) | 5 V | DC | Charging, data transfer |
Interactive Tools
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Related Terms
Electric Potential
Electric potential at a point in space is the amount of electric potential energy per unit positive test charge at that location, representing the work done per unit charge to bring a positive test charge from infinity to that point against the electric field. It is a scalar quantity measured in volts (V), where 1 volt equals 1 joule per coulomb. Electric potential is fundamental to understanding capacitors, batteries, and electrical circuits, and the difference in electric potential between two points (voltage) drives the flow of electric current.
Electric Field
An electric field is a vector field that exists in the region around an electric charge or a changing magnetic field, representing the electrostatic force that would be exerted per unit positive charge placed at any point in space. The field lines emanate outward from positive charges and point inward toward negative charges, with the density of field lines indicating field strength. Electric fields are central to understanding capacitors, electromagnetic waves, semiconductor devices, and the operation of all electrical equipment from simple circuits to complex communication systems.
Electric Charge
Electric charge is a fundamental intrinsic property of matter that causes particles to experience a force when placed in an electromagnetic field, existing as either positive (carried by protons) or negative (carried by electrons) with an elementary charge unit of e = 1.602 × 10⁻¹⁹ coulombs. Charge is conserved in all physical processes (the total charge of an isolated system remains constant), and it is quantised, meaning any observable charge is an integer multiple of the elementary charge. Electric charge is the source of the electric force, which is described by Coulomb's Law and governs all electromagnetic interactions in nature and technology.
Named after Alessandro Volta (1745–1827), the Italian physicist who invented the voltaic pile (first battery) in 1800. The term "potential difference" derives from Latin "potentia" (power) and "differentia" (distinction). The unit volt was officially adopted by the International Electrical Congress in 1881.