Voltage is a fundamental concept in the study of electricity, representing a measure of the energy available to drive an electric current through a circuit. It quantifies the difference in electric potential between two points, acting as the force that pushes charged particles to move. This potential difference is what ultimately allows work to be done by the flow of electricity.
The Primary Unit of Measurement
The standard international (SI) unit used to measure voltage is the volt, symbolized by the letter \(\text{V}\). This unit is named in honor of the Italian physicist Alessandro Volta, who invented the first electric battery, the voltaic pile, in 1800. One volt is defined in terms of energy and charge, representing one joule of energy per one coulomb of electric charge (\(\text{1 V} = \text{1 J/C}\)).
Understanding Electrical Potential
Voltage is often described as electric potential difference, which is the difference in the amount of potential energy per unit of charge between two points in an electric field. This concept is made clearer through an analogy involving gravity and water, where voltage is similar to water pressure. A greater height difference in a water tower, for example, results in higher water pressure at the bottom, just as a greater potential difference results in a higher voltage.
In an electrical circuit, a power source like a battery creates a separation of charge, establishing a high-potential point and a low-potential point. This separation acts like an electrical “push,” similar to how a pump creates the pressure difference in the water analogy. The difference in potential energy compels the charge, typically electrons, to flow from the high-potential point to the low-potential point through the external circuit.
Tools and Techniques for Measurement
The instrument specifically designed for measuring voltage is called a voltmeter. In practical applications, a multimeter, a versatile device capable of measuring current and resistance as well, is most commonly used as a voltmeter. To correctly measure the voltage across a component or a power source, the voltmeter must be connected in parallel with the part of the circuit being tested. This parallel connection is mandatory because voltage is a measure of the potential difference between two points.
To perform a measurement, the voltmeter’s probes are placed on either side of the component or source to tap into the two points of potential. If the voltage is measured across a source, such as a battery, the reading indicates the energy available to the circuit. If the measurement is taken across a load, like a light bulb or resistor, the reading shows the amount of electrical potential energy that is consumed or “dropped” by that specific component. Modern voltmeters have a very high internal resistance, which ensures that they draw a negligible amount of current from the circuit, preventing the measurement process from significantly altering the actual voltage being read.
Voltage in the Context of Electricity
Voltage is one of the three fundamental properties of an electric circuit, working in conjunction with current and resistance. The relationship between these three quantities is mathematically defined by Ohm’s Law, which states that voltage is equal to the product of current and resistance, expressed as \(V=IR\). This formula demonstrates that if the resistance in a circuit remains constant, increasing the voltage will cause the current to increase proportionally.
Voltage also appears in two distinct forms based on the nature of the electrical flow: Direct Current (\(\text{DC}\)) and Alternating Current (\(\text{AC}\)). \(\text{DC}\) voltage, typically supplied by batteries or solar panels, maintains a constant polarity, meaning the current flows in a single, unwavering direction. In contrast, \(\text{AC}\) voltage, which is delivered by wall outlets in homes and businesses, periodically reverses its polarity, causing the current to rapidly change its direction of flow. This periodic reversal creates a sinusoidal wave pattern, typically cycling at \(\text{50}\) or \(\text{60}\) hertz depending on the region.