electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

, voltage drop is the decrease of

electric potential Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...

along the path of a

current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (hydr ...

flowing in a circuit.

Voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

drops in the

internal resistance In electrical engineering, a practical electric power source which is a linear circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This impedance is termed the internal resis ...

of the

source Source may refer to: Research * Historical document * Historical source * Source (intelligence) or sub source, typically a confidential provider of non open-source intelligence * Source (journalism), a person, publication, publishing institute ...

, across conductors, across

contacts Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic ...

, and across connectors are undesirable because some of the energy supplied is

dissipated In thermodynamics, dissipation is the result of an irreversible process that affects a thermodynamic system. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to a final form, wher ...

. The voltage drop across the load is proportional to the

power Power may refer to: Common meanings * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power, a type of energy * Power (social and political), the ability to influence people or events Math ...

available to be converted in that load to some other useful form of energy. For example, an electric

space heater A space heater is a device used to heat a single, small- to medium-sized area. This type of heater can be contrasted with central heating, which distributes heat to multiple areas. Types Dominant mode of heat transfer All space heaters t ...

may have a resistance of 10

ohm Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm. Ohm or OHM may also refer to: People * Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm'' * Germán Ohm (born 1936), Mexican boxer * Jörg Ohm (1 ...

s, and the wires that supply it may have a resistance of 0.2 ohms, about 2% of the total circuit resistance. This means that approximately 2% of the supplied voltage is lost in the wire itself. An excessive voltage drop may result in the unsatisfactory performance of the space heater and the overheating of the wires and connections. National and local

electrical code An electrical code is a term for a set of regulations for the design and installation of electrical wiring in a building. The intention of such regulations is to provide standards to ensure electrical wiring systems are safe for people and propert ...

s may set guidelines for the maximum voltage drop allowed in

electrical wiring Electrical wiring is an electrical installation of Electrical cable, cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure. Wiring is subject to safety standards for design and in ...

to ensure efficiency of distribution and proper operation of electrical equipment. The maximum permitted voltage drop varies from one country to another. In electronic design and

power transmission Power transmission is the movement of energy from its place of generation to a location where it is applied to perform useful Mechanical work, work. Power (physics), Power is defined formally as units of energy per unit time. In SI units: :\text ...

, various techniques are employed to compensate for the effect of voltage drop on long circuits or where voltage levels must be accurately maintained. The simplest way to reduce voltage drop is to increase the diameter of the conductor between the source and the load, which lowers the overall resistance. In

power distribution Electric power distribution is the final stage in the delivery of electricity. Electricity is carried from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission v ...

systems, a given amount of power can be transmitted with less voltage drop if a higher voltage is used. More sophisticated techniques use active elements to compensate for excessive voltage drop.

Resistive DC voltage drop

Ohm's law Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of ...

can be used to determine the DC voltage drop by multiplying current times resistance: . Also,

Kirchhoff's circuit laws Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirc ...

state that in any DC circuit, the sum of the voltage drops across each component of the circuit is equal to the supply voltage. Consider a direct-current circuit with a nine-volt DC source; three

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

s of 67

s, 100 ohms, and 470 ohms; and a light bulb—all connected in

series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used i ...

. The DC source, the conductors (wires), the resistors, and the light bulb (the load) all have resistance; all use and dissipate supplied energy to some degree. Their physical characteristics determine how much energy. For example, the DC resistance of a conductor depends upon the conductor's length, cross-sectional area, type of material, and temperature. If the voltage between the DC source and the first resistor (67 ohms) is measured, the voltage potential at the first resistor will be slightly less than nine volts. The current passes through the conductor (wire) from the DC source to the first resistor; as this occurs, some of the supplied energy is "lost" (unavailable to the load), due to the resistance of the conductor. Voltage drop exists in both the supply and return wires of a circuit. If the voltage drop across each resistor is measured, the measurement will be a significant number. That represents the energy used by the resistor. The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor.

Reactive AC voltage drop

AC voltages additionally have a second kind of opposition to current flow: reactance. The sum of resistance and reactance is called impedance. Electrical impedance is commonly represented by the variable ''Z'' and measured in ohms at a specific frequency. Electrical impedance is computed as the

vector Vector most often refers to: * Euclidean vector, a quantity with a magnitude and a direction * Disease vector, an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematics a ...

sum of

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual paral ...

capacitive reactance In electrical circuits, reactance is the opposition presented to alternating current by inductance and capacitance. It's measured in Ω (Ohms). Along with resistance, it is one of two elements of impedance; however, while both elements involve ...

, and

inductive reactance In electrical circuits, reactance is the opposition presented to alternating current by inductance and capacitance. It's measured in Ω (Ohms). Along with resistance, it is one of two elements of impedance; however, while both elements involve ...

. The amount of impedance in an alternating-current circuit depends on the frequency of the alternating current and the magnetic permeability of electrical conductors and electrically isolated elements (including surrounding elements), which varies with their size and spacing. Analogous to

for direct-current circuits, electrical impedance may be expressed by the formula . So, the voltage drop in an AC circuit is the product of the current and the impedance of the circuit.

Diode voltage drop

Forward-biased p–n junctions in

diodes A diode is a two- terminal electronic component that conducts electric current primarily in one direction (asymmetric conductance). It has low (ideally zero) resistance in one direction and high (ideally infinite) resistance in the other. ...

and

transistors A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

experience a voltage drop that is slightly above the diode's threshold voltage. The energy is dissipated through

photons A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that ...

, which for the case of

light-emitting diodes A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

are emitted and visible.

References

*Electrical Principles for the Electrical Trades (Jim Jennesson) 5th edition Electrical parameters

Drop Drop, DROP, drops or DROPS may refer to: * Drop (liquid) or droplet, a small volume of liquid ** Eye drops, saline (sometimes mydriatic) drops used as medication for the eyes * Drop (unit), a unit of measure of volume * Falling (physics), allowing ...

Resistive DC voltage drop

Reactive AC voltage drop

Diode voltage drop

See also

References