Voltage
Voltage, often referred to as electric potential, is the force that drives the flow of electrons in an electrical circuit. It is measured in joules per coulomb, where one volt signifies a force that pushes one coulomb of charge through a medium with one ohm of resistance in one second. The concept of voltage is rooted in the difference in charge between two points, indicating the energy required to move a charge between them. Voltage can be classified into two types: alternating voltage, which reverses polarity periodically, and direct voltage, which maintains a constant polarity.
Devices such as voltmeters are used to measure voltage by connecting multiple points in a circuit, while the flow of electrical current typically occurs from areas of higher charge to lower charge. An analogy often used is that of water pressure in a hose, where voltage represents the pressure that drives the flow of water (current). Furthermore, voltage is crucial in calculations related to Ohm's law, which describes the relationship between voltage, current, and resistance. Understanding voltage is essential for safe and effective use of electrical devices, as higher voltages can pose significant safety risks. For example, voltages above fifty volts can be lethal, particularly under certain conditions.
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Voltage
Voltage is typically referred to as electric potential, the force that instigates the flow of electrons through a circuit. This quantity is measured as a per-unit charge and is given in joules per coulomb; in other words, one volt pushes a single coulomb of charge carriers through a medium with one ohm of resistance in one second. Voltage is an indication of the difference in charge between any two points, and it shows the energy, or work, required to move a specified charge between those two points. Voltage takes its name from Alessandro Volta (1745–1827), an Italian scientist who is best known for studying electrical capacitance. He also invented the voltaic pile, a crude battery.
Generally speaking, the greater the voltage, the greater the corresponding flow of electrical current through the conducting medium at a given resistance. This is known as Ohm’s law. The actual charge of either of the two points in space is less relevant than the difference between the two points’ potential electric energy; thus, voltage is always relative to the points that have been selected.
Background
There are two types of voltage: alternating and direct. With alternating voltage, from time to time the polarity reverses direction, as happens with outlets used to provide power in homes. Direct voltage, in contrast, does not reverse direction, instead maintaining the same polarity continuously.
The device used to measure voltage is called a voltmeter, and it is attached to multiple points, such as battery leads, in order to measure the difference in charge between them. Other devices that are sometimes used to measure voltage are the potentiometer and the cathode-ray oscilloscope.
Voltage is studied in terms of positive and negative charges. These opposing charges attract one another, so electrical current flows from objects with positive charges to objects with lower charges and from objects with higher charges to objects with negative charges. The flow is typically from high to low, but it is also possible for the charge to move from low to high if there is an additional source of energy to help the charge move against the opposing electrical field. If two points with the same potential energy are connected by a conducting material, no current will flow between them because the difference in charges is zero.
Overview
One often thinks of a battery as a device used to store energy. (The reality is slightly more complicated, but this serves as a satisfactory explanation of how the concept of voltage becomes meaningful when applied to a real-world situation.) A battery contains two different materials. One of the materials essentially has excess electrons. Because electrons carry a single negative charge each, a substance with too many electrons accumulates the negative charges into one large negative charge. The other material in the battery lacks electrons, which produces a positive charge.
If these two different materials are connected by a conductor, which is a substance that allows electrons to flow along it, then the electrons tend to flow from negative to positive, as if seeking to attain a balanced state in which both materials have the same, or close to the same, charge. The rate at which the electrons in this situation will flow across the conductor depends on how great the difference is between the charges of the two materials. If there is a small difference in charge, then the flow will be weaker; if there is a large difference, then the flow will be stronger. Voltage is the value used to measure the difference between the charges of the two materials.
An analogy that is often used to clarify how voltage operates is that of water flowing through a garden hose. The reason that water starts flowing out of the hose when the faucet is turned on is because the water is stored under pressure; when a channel is opened, the pressure pushes the water out of its container and through that channel (the hose). In this analogy, if there were a way of measuring the amount of pressure applied to the stored water, that pressure measurement would be akin to what is meant by voltage, while the strength of the flow of the water would be akin to current. Thus, pressure (voltage) increases as the flow (current) is restricted.
Voltage is often used in calculations based on Ohm’s law, which encapsulates the relationships between flow, pressure, and resistance by proving that there is a direct linear relationship between the current flowing from one point to another along a conductor and the difference in potential energy between those two points, given constant resistance. Ohm’s law is named after its creator, German physicist Georg Ohm (1789–1854), who conducted experiments using voltaic piles connected by wires of different lengths and discovered a way to mathematically express the relationship between voltage, current, and resistance.
The degree of danger posed by a particular source of electrical energy may sometimes be expressed in terms of the source’s voltage. Voltages of fifty and higher are lethal; lower voltages can be deadly if they come into contact with wet or broken skin, but this depends on the circumstances, including whether insulating materials are near the point of contact. The voltage of most batteries in household use (such as AA, C, or D) is 1.2 to 1.5 volts during discharge.
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