Current Definition: Meaning, Formula & Examples
Electric current describes the rate at which electric charge flows through a conductor or electrical circuit. It is one of the most fundamental ideas in electricity and electronics because almost every electrical device depends on controlled movement of charge. When a battery powers a flashlight, a charger supplies energy to a phone, or electricity passes through household wiring, current is flowing somewhere in the circuit. Current is represented by the symbol I and is measured in amperes, commonly shortened to amps or written as A. Understanding current makes concepts such as voltage, resistance, electrical power, and circuit behavior much easier to understand.
At a basic level, current occurs when electrically charged particles move through a material. In metallic conductors such as copper wires, these moving charges are primarily electrons. A voltage difference creates an electric field that encourages charge movement through the conductive material. The amount of charge passing a particular point during a given period determines the current. More charge passing per second means a larger current, while less charge passing per second means a smaller current. This relationship is expressed mathematically through the fundamental electric current formula, which connects charge and time.
Electric current appears in several forms, but the two most familiar are direct current and alternating current. Direct current, or DC, maintains one general direction of charge flow and is commonly associated with batteries, electronic circuits, solar systems, and many low-voltage devices. Alternating current, or AC, changes direction periodically and is widely used for electricity distribution in homes, offices, factories, and power networks. Although their behavior differs, both forms represent movement of electric charge. Understanding their differences helps explain why different power sources and electrical systems are designed in different ways.
Current is closely related to voltage and resistance through Ohm’s law. Voltage provides the potential difference that can drive charge through a circuit, while resistance opposes current flow. If voltage increases while resistance remains constant, current increases. If resistance increases while voltage stays constant, current decreases. These relationships allow technicians, engineers, students, and hobbyists to calculate expected circuit behavior. They also help explain why components such as resistors, fuses, circuit breakers, and conductors need appropriate ratings for safe operation.
This guide explains the current definition, current formula, unit of current, current calculations, AC and DC current, Ohm’s law, measurement methods, and practical examples. It also explores how current differs from voltage, resistance, and electrical power. The explanations are designed to be accessible to beginners while remaining useful for anyone refreshing their understanding of basic electrical concepts. By understanding how charge, time, voltage, and resistance interact, you can interpret many everyday electrical situations much more confidently. Current may be invisible, but its effects are present throughout modern technology.
What Is Electric Current?
Electric current is the rate of movement of electric charge through a particular point or cross-section of a conductor. The word rate is important because current describes not simply whether charge is moving but how much charge passes during a certain amount of time. In an electrical wire, large numbers of electrons can move as a result of an electric field created by a voltage source. Their collective movement produces electric current. The amount of current can vary depending on the voltage applied, the resistance of the circuit, and other physical characteristics. Current is therefore a measurable quantity rather than simply a description of electricity being present.
The standard symbol used for electric current is I. This notation appears in circuit diagrams, equations, textbooks, electrical specifications, and engineering calculations. The SI unit of current is the ampere, represented by the symbol A. One ampere corresponds to one coulomb of electric charge passing a point per second. Smaller electrical currents may be expressed in milliamperes, abbreviated mA, or microamperes, abbreviated µA. Larger industrial currents can reach hundreds or thousands of amperes depending on the equipment and application involved.
Current requires a complete conductive path in most ordinary circuits. Consider a simple circuit containing a battery, wires, a switch, and a lamp. When the switch is open, the path is interrupted and sustained current cannot flow around the complete circuit. Closing the switch completes the pathway, allowing the battery’s potential difference to establish current through the lamp. Electrical energy is transferred to the lamp, where it can be converted into light and heat. This basic example illustrates why switches control electrical devices by opening or closing current paths.
In metals, current is associated with the movement of electrons, but electric current is not limited to metallic conductors. In electrolytes, positive and negative ions can carry charge through a liquid. In semiconductors, current can involve electrons and charge carriers described as holes. In gases and plasmas, ions and electrons can participate in conduction under suitable conditions. The general definition remains the same regardless of the particular charge carriers involved. Electric current measures the rate of charge flow, not one specific type of particle.
Current is essential because electrical devices need controlled charge movement to perform useful functions. Motors use current to create electromagnetic effects that produce motion. Heating elements convert electrical energy into heat as current passes through resistance. Electronic processors control tiny currents through semiconductor components to perform computations. Batteries deliver current to portable devices, while electrical grids supply current to homes and industries. From microscopic integrated circuits to enormous industrial machinery, current remains one of the central quantities used to describe electrical operation.
Electric Current Formula Explained
The fundamental current formula is based on the amount of electric charge passing through a point over time. Current can be expressed as I = Q ÷ t, where I represents current in amperes, Q represents electric charge in coulombs, and t represents time in seconds. This equation shows that current increases when a greater amount of charge passes through the same point during the same interval. It also shows that the same amount of charge produces less current when it takes longer to pass. The formula provides a direct mathematical definition of electric current.
Suppose 10 coulombs of electric charge pass through a wire in 5 seconds. Using the formula I = Q ÷ t, the current would be 10 divided by 5, giving 2 amperes. If the same 10 coulombs passed in only 2 seconds, the current would be 5 amperes. The amount of total charge has not changed, but the rate at which the charge passes has increased. This is why electric current is properly described as a rate. The concept is similar to measuring how much water passes through a pipe during a particular time interval.
The ampere can therefore be understood directly from the relationship between charge and time. A current of 1 ampere represents 1 coulomb of charge passing through a point every second. Two amperes represent 2 coulombs per second, while half an ampere represents 0.5 coulomb per second. Because a coulomb represents an enormous number of elementary charges, even relatively small everyday currents involve the movement of vast numbers of charge carriers. Electrical measurements summarize this microscopic activity using practical units.
For currents that change continuously over time, the simple average formula may not describe every instant accurately. In more advanced physics and engineering, instantaneous current can be described using the rate of change of charge with respect to time. However, beginners usually work first with I = Q ÷ t because it clearly establishes the meaning of current. Later study of alternating signals, capacitors, electronics, and electromagnetic systems introduces more detailed mathematical descriptions. The basic relationship remains the conceptual foundation.
When using the formula, it is important to keep the units consistent. Charge should usually be expressed in coulombs and time in seconds when the answer is required in amperes. If time is given in minutes, it should be converted into seconds before applying the equation. Similarly, milliampere values may need conversion depending on the problem. Careful unit handling prevents simple calculation mistakes. Understanding the meaning of the equation is ultimately more valuable than memorizing it without recognizing what each quantity represents.
Current and Ohm’s Law
A second widely used way to calculate current comes from Ohm’s law. The familiar equation is V = I × R, where V represents voltage, I represents current, and R represents resistance. Rearranging the equation to solve for current gives I = V ÷ R. This relationship is extremely useful because electrical circuits are often described using voltage and resistance rather than total charge passing over time. If the voltage across a resistor and its resistance are known, current can usually be calculated directly.
Imagine a 12-volt source connected across a 6-ohm resistor. Using I = V ÷ R, the current equals 12 divided by 6, which gives 2 amperes. If the resistance increases to 12 ohms while the voltage remains 12 volts, the current decreases to 1 ampere. This demonstrates the inverse relationship between current and resistance when voltage remains unchanged. Greater resistance makes it more difficult for charge to move through the circuit. Lower resistance allows more current under the same applied voltage.
Voltage also strongly influences current. Suppose resistance remains fixed at 10 ohms. A 5-volt source would produce 0.5 ampere through an ideal ohmic resistor, while a 10-volt source would produce 1 ampere. Doubling the voltage doubles the current when resistance remains constant. This proportional relationship is one reason electrical systems must be designed for specific operating voltages. Applying excessive voltage can force more current through components than they are designed to handle.
Ohm’s law works directly for components whose resistance remains reasonably constant under the conditions being considered. Many resistors behave approximately this way within their intended operating range. However, not every electrical component has a constant resistance. Diodes, transistors, lamps, thermistors, and many other devices can have nonlinear voltage-current relationships. Temperature can also change resistance significantly. Ohm’s law remains fundamental, but real circuits may require more information than one fixed resistance value.
The relationship between voltage, current, and resistance is central to circuit troubleshooting. If a device draws much more current than expected, technicians may investigate whether resistance has decreased because of a short circuit or component failure. If current is too low, excessive resistance, broken connections, or insufficient voltage may be responsible. Measuring multiple electrical quantities helps narrow down the fault. Ohm’s law therefore serves not only as a classroom formula but also as a practical diagnostic tool in electrical and electronic work.
Direct Current vs Alternating Current
Direct current, or DC, refers to current that maintains one overall direction of charge flow. Batteries are familiar sources of direct current because their terminals maintain defined polarity while delivering energy. Many electronic devices operate internally using DC even when they receive power from an AC wall outlet. Chargers and power supplies convert incoming electricity into suitable DC voltage and current for electronic circuits. Solar panels also naturally generate direct current, which may later be converted depending on how the electricity will be used.
Alternating current, or AC, repeatedly changes direction over time. The voltage and current in common power systems typically vary in a repeating waveform. In many electrical grids, this alternating behavior occurs dozens of times each second according to the system frequency. AC became widely used for power distribution because voltage can be transformed efficiently for transmission and local use. High-voltage transmission helps move large amounts of electrical power over long distances with manageable losses. Transformers can then adjust voltage to appropriate levels for distribution and equipment.
The difference between AC and DC does not mean that one is fundamentally more electrical than the other. Both involve electric charge and can transfer energy to loads. Their waveform and direction behavior differ, which affects how circuits are designed and analyzed. DC is convenient for batteries, electronics, and many low-voltage systems. AC is well suited to large power networks and many motors, appliances, and industrial systems. Modern electrical infrastructure frequently converts between the two forms as needed.
Current magnitude in AC systems requires additional interpretation because the instantaneous value changes continuously. A sinusoidal alternating current rises, falls, reverses direction, and repeats according to its frequency. Electrical measurements commonly use root-mean-square values to describe an equivalent effective magnitude for power-related purposes. This allows AC voltages and currents to be compared meaningfully with DC in many practical calculations. Peak values are higher than corresponding RMS values for a sinusoidal waveform. Understanding the distinction becomes important in more advanced electrical work.
Many modern systems combine AC and DC technologies. A laptop charger receives AC from the power outlet but supplies regulated DC to the computer. An electric vehicle battery stores energy as DC, while power electronics control current for charging and motor operation. Solar installations generate DC and often use inverters to produce AC for buildings or the electrical grid. Data centers similarly rely on multiple stages of conversion and distribution. Understanding both current types therefore provides a better picture of how contemporary electrical systems actually operate.
How Is Electric Current Measured?
Electric current is commonly measured using an ammeter or a multimeter configured for current measurement. Unlike voltage measurement, which is typically taken across two points, current measurement traditionally requires the meter to become part of the current path. This means the circuit may need to be opened and the meter connected in series so the same current passes through the measuring instrument. Incorrect connection can damage the meter or create a hazardous short circuit. Users should therefore understand both the instrument and the electrical system before attempting a current measurement.
A digital multimeter usually provides several input terminals and selectable measurement ranges. The test lead used for current measurement may need to be moved to a dedicated amperage input rather than remaining in the voltage-resistance terminal. Some meters have separate inputs for small currents and higher currents. Selecting an inappropriate input or range can blow the meter’s internal fuse or damage equipment. Professional meters often include protective features, but these do not replace correct procedures. The manufacturer’s instructions should be followed carefully.
For larger currents, technicians often use a clamp meter rather than disconnecting the circuit. A clamp meter measures the magnetic field associated with current flowing through a conductor and converts that information into a current reading. This can make measurements faster and safer in many situations because the wire does not need to be electrically opened. The clamp usually surrounds one conductor rather than an entire cable containing both outgoing and returning conductors. Clamping around both can cause magnetic fields to cancel and produce an incorrect reading.
Current measurement becomes more complicated in AC circuits, rapidly changing signals, and electronic systems. Some meters are designed to provide accurate RMS measurements for standard waveforms, while others may be less accurate with distorted signals. Oscilloscopes combined with current probes can display how current changes over time. Engineers may also measure voltage across a known low-value shunt resistor and calculate current from that voltage. The appropriate technique depends on current magnitude, frequency, accuracy requirements, and circuit design.
Safety becomes especially important when measuring current in mains-powered or high-energy systems. A meter inserted incorrectly across a voltage source while configured for current measurement can create a very low-resistance path and cause dangerous fault current. High-voltage installations can present risks of shock, arc flash, burns, or equipment damage. People without appropriate training should not open or probe hazardous electrical systems. Understanding the definition of current is useful for everyone, but practical measurement should always respect the risks associated with electrical energy.
Current Examples in Everyday Electrical Systems
A small LED provides a simple example of electric current in everyday electronics. Many indicator LEDs operate using currents measured in milliamperes rather than whole amperes. A resistor or electronic driver limits the current so the LED receives an appropriate amount. Too little current may make the LED dim, while excessive current can overheat and damage it. This example illustrates an important principle: electrical components are often designed to operate within a specific current range. Current control is therefore fundamental to electronic circuit design.
A smartphone provides another familiar example. Its battery stores energy chemically and supplies direct current to internal circuits. Different components require different voltage and current levels, so power-management electronics regulate electricity throughout the device. The processor, display, wireless radios, cameras, storage, and other components all contribute to overall power consumption. During demanding activities, the device may draw more current from the battery than it does while idle. This increased current contributes to faster battery discharge.
Household appliances can involve substantially larger currents. A small electronic charger may draw relatively little current from an outlet, while an electric heater, kettle, oven, or air conditioner can require much more. Heating appliances often have significant power demands because electrical energy is intentionally converted into heat. Wiring, plugs, switches, fuses, and circuit breakers must therefore be sized for expected current. If current exceeds safe levels, protective devices are designed to interrupt the circuit under defined conditions.
Automobiles also provide many examples of current. A vehicle battery may need to provide very high current briefly when operating the starter motor. Smaller electrical loads power lights, sensors, entertainment systems, computers, pumps, and control modules. Modern electric and hybrid vehicles operate with much more sophisticated high-voltage battery systems and power electronics. Their motors can draw substantial currents, particularly during acceleration. These systems require careful thermal management, insulation, current sensing, and protective devices.
Industrial equipment can operate at currents ranging from tiny sensor signals to extremely large motor or power-system currents. Electric motors draw current according to their load and operating conditions, and starting current can differ significantly from normal running current. Automation systems monitor these values to identify faults or overloads. Protective relays and circuit breakers can disconnect equipment when unsafe conditions occur. Current measurement therefore supports both operation and preventive maintenance. These examples demonstrate how the same basic electrical quantity applies from miniature electronics to industrial power systems.
Current vs Voltage vs Resistance
Current, voltage, and resistance are closely related but describe different electrical concepts. Current measures the rate of electric charge flow, voltage represents electrical potential difference, and resistance describes opposition to current flow. These quantities interact according to circuit conditions. Confusing them can make even simple electrical explanations difficult to follow. A useful starting point is to think of voltage as a driving potential, current as the resulting charge flow, and resistance as something that limits that flow.
A water analogy is sometimes used to introduce these concepts. Voltage can be compared loosely to pressure pushing water through a pipe, current to the rate of water flow, and resistance to restrictions that make flow more difficult. This analogy can help beginners develop intuition, but it should not be taken literally because electrical behavior differs from fluid systems in important ways. Electricity involves electric fields and charge carriers rather than water molecules. The analogy is useful mainly for understanding relationships between quantities.
Ohm’s law provides the mathematical connection for many basic resistive circuits. Current equals voltage divided by resistance, which means increasing voltage tends to increase current if resistance remains constant. Increasing resistance tends to decrease current if voltage remains unchanged. This simple relationship explains why resistors can limit current and why low-resistance faults can create dangerously high currents. It also demonstrates why electrical values must be considered together rather than independently. A current reading often makes more sense when voltage and resistance are also known.
Resistance itself depends on several physical factors. The material of a conductor matters because some materials allow charge movement more easily than others. Length and cross-sectional area also influence resistance, with longer conductors generally providing greater resistance and thicker conductors providing less. Temperature can change resistance as well, particularly in metallic conductors. These effects influence current throughout real electrical systems. Engineers therefore select conductor sizes and materials according to current, voltage drop, temperature, safety, and installation requirements.
Understanding the three quantities helps prevent a common misconception that a voltage source simply pushes a fixed current into every device. In reality, the current drawn depends on the connected load and circuit characteristics. A device designed for a particular voltage presents an electrical behavior that determines how much current it takes under operating conditions. Connecting an inappropriate load can cause excessive current or incorrect operation. Current, voltage, and resistance should therefore be considered as interconnected parts of circuit behavior rather than isolated numbers.
Current and Electrical Power
Electric current is closely connected to electrical power, but the two are not the same quantity. Current measures charge flow, while power measures the rate at which electrical energy is transferred or converted. One commonly used power equation is P = V × I, where P represents power in watts, V represents voltage in volts, and I represents current in amperes. This means power depends on both voltage and current. A high current does not automatically mean high power unless the voltage is also considered.
Suppose a device operates at 12 volts and draws 2 amperes. Using P = V × I, its electrical power is 24 watts. Another device operating at 120 volts while drawing 2 amperes would use 240 watts. The current is identical in both examples, but the voltage differs substantially, causing the power to differ. This illustrates why comparing current ratings without considering voltage can be misleading. Electrical systems often specify both values so users understand operating requirements.
Current can also produce heating in conductors and resistive components. The power dissipated in a resistance can be related to current through formulas derived from Ohm’s law. As current increases, resistive heating can increase significantly. This is one reason electrical conductors need sufficient cross-sectional area for their expected current. A wire that is too small for a heavy load can overheat. Appropriate circuit protection helps limit the duration of excessive-current conditions.
Electrical power consumption also influences the current drawn by household appliances. At a given supply voltage, a higher-power appliance generally requires more current than a lower-power appliance. This helps explain why high-powered heaters, cooking equipment, and air-conditioning systems may require dedicated electrical circuits. Circuit breakers and wiring are selected according to expected current and installation standards. Trying to operate too many high-power devices from one circuit can exceed its intended capacity and cause protective devices to trip.
Energy is related to power over time rather than to current alone. An appliance using a certain number of watts for several hours consumes more energy than the same appliance running briefly. Electricity billing commonly reflects energy consumption using kilowatt-hours. Current contributes to power and therefore indirectly to energy use, but it should not be confused with either. Recognizing the difference between amperes, watts, and kilowatt-hours makes electrical specifications much easier to interpret.
Factors That Affect Electric Current
Voltage is one of the main factors affecting electric current in a resistive circuit. When the applied voltage increases and resistance remains approximately constant, the current increases. A stronger potential difference creates a stronger electric field that influences charge movement through the conductor. This relationship can be predicted using Ohm’s law for suitable components. However, real devices may change their electrical characteristics as voltage changes. Engineers therefore use component-specific behavior rather than assuming every circuit remains perfectly linear.
Resistance is another major factor. Higher resistance opposes current flow more strongly, reducing the current for a given voltage. Lower resistance allows greater current under the same voltage. Resistors are deliberately added to circuits when current must be limited or voltages need to be divided. Unwanted resistance in connectors or damaged wiring can reduce performance and create localized heating. Extremely low resistance can produce a short circuit and cause dangerously high current.
Temperature can affect current because many materials change resistance as they heat or cool. Metallic conductors typically increase in resistance as temperature rises. This means the current through a conductor can change if the voltage remains constant while the conductor becomes hotter. Semiconductor components can exhibit more complex temperature behavior. These relationships are important in electronics, motors, power distribution, and battery systems. Thermal design and electrical design therefore often need to be considered together.
Conductor geometry also matters. A longer wire generally has more electrical resistance than a shorter wire made from the same material and with the same thickness. A larger cross-sectional area generally reduces resistance because more conductive pathway is available. This is why heavy-current circuits typically use thicker conductors. The required conductor size depends on current, material, length, acceptable voltage drop, environmental conditions, and applicable electrical standards. Choosing wire size only by appearance can be unsafe.
The nature of the electrical load also determines current. A fixed resistor behaves differently from a motor, capacitor, LED, computer power supply, or heating element. Some loads draw a large brief current when first switched on and then settle to a lower operating value. Others change current dynamically according to processing activity or mechanical load. Accurate current prediction therefore requires understanding the device as well as the supply voltage. Real electrical systems are more complex than one simple resistance connected to a battery.
Why Electric Current Matters for Electrical Safety
Electric current is directly connected to electrical safety because excessive current can overheat wires, damage components, start fires, and create serious hazards. Conductors have limits on how much current they can carry safely under particular conditions. If too much current flows for too long, resistive heating can raise the temperature of the wire and surrounding materials. Electrical systems therefore use protective devices designed to disconnect abnormal current. Proper design considers both normal operating current and possible fault conditions.
Fuses protect circuits by containing an element designed to open when current exceeds an appropriate level for a sufficient period. Once a fuse operates, it generally must be replaced. Circuit breakers perform a related function but can usually be reset after the fault has been corrected. Different protective devices have different operating characteristics, so their current rating alone does not describe every aspect of protection. Engineers select them according to conductor capacity, equipment behavior, expected starting currents, and fault conditions.
A short circuit can create particularly large current because the fault path may have very low resistance. According to the basic relationship between voltage, current, and resistance, reducing resistance dramatically can increase current if the source can supply it. The resulting fault can generate intense heating, sparks, arcs, or equipment damage. Protective devices are designed to interrupt these conditions quickly enough to reduce risk. This explains why bypassing fuses or installing an incorrectly rated breaker can be dangerous.
Electric shock risk also involves current passing through the human body, but safety cannot be reduced to one universal current threshold. The effect depends on current magnitude, path through the body, duration, frequency, skin condition, contact area, and other circumstances. Even common electrical systems can cause severe injury or death. People should never intentionally test electrical current using their bodies or assume a voltage is harmless based only on familiarity. Qualified procedures and suitable protective equipment are essential around hazardous installations.
Understanding current encourages safer decisions even for non-specialists. It explains why extension leads have ratings, why overloaded outlets are risky, why damaged wiring should be repaired, and why circuit protection should not be defeated. However, conceptual understanding does not qualify someone to perform high-voltage electrical work. Household mains systems and industrial installations should be serviced according to applicable electrical codes and professional safety practices. Electricity is highly useful precisely because it can transfer significant energy, and that capability deserves appropriate respect.
Conclusion
Electric current is the rate at which electric charge flows through a point in an electrical system. It is represented by the symbol I and measured in amperes, or amps. The fundamental definition can be expressed using charge and time, while Ohm’s law allows current to be calculated from voltage and resistance in many basic circuits. These relationships provide the foundation for understanding electrical behavior. Current appears throughout electronics, household wiring, transportation, communications, renewable energy systems, and industrial equipment.
The basic current formula shows that more charge passing during a shorter time produces a larger current. One ampere corresponds to one coulomb of charge passing a point each second. This simple definition connects microscopic charge movement with the electrical measurements used in real devices. For practical circuit calculations, I = V ÷ R is often used when voltage and resistance are known. Both equations describe current from different but complementary perspectives.
Current can be either direct or alternating depending on the electrical system. Direct current maintains one overall direction and is common in batteries and electronic circuits. Alternating current changes direction periodically and is widely used for power generation and distribution. Many modern devices use both forms at different stages, converting AC to DC or DC to AC when necessary. Understanding these current types helps explain how everyday electrical equipment receives and uses energy.
Current should also be distinguished from voltage, resistance, power, and energy. Voltage represents potential difference, resistance opposes current, and power represents the rate of energy transfer. These quantities interact closely, which is why electrical calculations often involve several of them simultaneously. Measuring one quantity can help diagnose problems involving another. Learning how they connect is more useful than memorizing isolated definitions. The relationships form the basis of practical circuit analysis.
Ultimately, understanding the current definition, formula, units, and examples provides an essential starting point for learning electricity. Current explains how electrical charge moves through circuits and how devices receive the energy needed to operate. It also helps explain protective devices, wiring requirements, power consumption, and electrical safety. Whether you are studying physics, learning electronics, or simply interpreting appliance specifications, the concept appears everywhere. Once current is understood clearly, more advanced electrical topics become considerably easier to approach.
Frequently Asked Questions About Electric Current
What is current in simple words?
Electric current is the rate at which electric charge moves through a conductor or circuit. It is commonly represented by the symbol I and measured in amperes.
What is the formula for electric current?
The fundamental formula is I = Q ÷ t, where I is current, Q is electric charge, and t is time. Current can also be calculated using Ohm’s law as I = V ÷ R when voltage and resistance are known.
What is the unit of current?
The SI unit of electric current is the ampere, represented by A. Smaller currents are often expressed in milliamperes or microamperes.
What is the difference between current and voltage?
Current measures the rate of electric charge flow, while voltage represents electrical potential difference between two points. Voltage can drive current through a circuit, while the resulting amount of current depends on the electrical characteristics of the circuit.
What are examples of electric current?
Examples include current flowing from a battery through a flashlight, current powering a smartphone circuit, AC current supplying household appliances, and high current operating an industrial motor. The magnitude and type of current vary according to the device and electrical system.
