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External electric load

 

 
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External electric load
 
 
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If an electric circuit
Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches....
 has a well-defined output terminal, the circuit connected to this terminal (or its input impedance
Input impedance

The input Electrical_impedance, Electrical load impedance, or external impedance of a electrical network or electronic device is the Th?venin's theorem electrical impedance looking into its input....
) is the load. (The term 'load' may also refer to the power
Power (physics)

In physics, power is the rate at which mechanical work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time....
 consumed by a circuit; that topic is not discussed here.)

Load affects the performance of circuits that output voltage
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
s or currents, such as sensor
Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube....
s, voltage source
Voltage source

A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force....
s, and amplifier
Amplifier

Generally, an amplifier or simply amp, is any machine that changes, usually increases, the amplitude of a Signal . The "signal" is usually voltage or current....
s. A household's power outlet
Domestic AC power plugs and sockets

AC power plugs and sockets are devices for removably connecting electrically-operated devices to the mains electricity.An electric plug is a gender of connectors and fasteners electrical connector with contact prongs to connect mechanically and electrically to slots in the matching female socket....
s provide an easy example: they are a voltage source, outputting 120 V
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
 AC
Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
 for example (in USA), with the household's appliances collectively making up the load.






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If an electric circuit
Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources, and switches....
 has a well-defined output terminal, the circuit connected to this terminal (or its input impedance
Input impedance

The input Electrical_impedance, Electrical load impedance, or external impedance of a electrical network or electronic device is the Th?venin's theorem electrical impedance looking into its input....
) is the load. (The term 'load' may also refer to the power
Power (physics)

In physics, power is the rate at which mechanical work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time....
 consumed by a circuit; that topic is not discussed here.)

Load affects the performance of circuits that output voltage
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
s or currents, such as sensor
Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube....
s, voltage source
Voltage source

A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force....
s, and amplifier
Amplifier

Generally, an amplifier or simply amp, is any machine that changes, usually increases, the amplitude of a Signal . The "signal" is usually voltage or current....
s. A household's power outlet
Domestic AC power plugs and sockets

AC power plugs and sockets are devices for removably connecting electrically-operated devices to the mains electricity.An electric plug is a gender of connectors and fasteners electrical connector with contact prongs to connect mechanically and electrically to slots in the matching female socket....
s provide an easy example: they are a voltage source, outputting 120 V
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
 AC
Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
 for example (in USA), with the household's appliances collectively making up the load. When a power-hungry appliance switches on, it dramatically reduces the load impedance
Electrical impedance

Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current . Electrical impedance extends the concept of Electrical resistance to AC circuits, describing not only the relative amplitudes of the voltage and Electric current, but also the relative Phase ....
, causing the output voltage to drop. This drop is easily observed; for instance, turning on a vacuum cleaner
Vacuum cleaner

A vacuum cleaner is a device that uses an air pump to create a partial vacuum to suck up dust and dirt, usually from floors.Most homes with carpeted floors in developed countries possess a vacuum cleaner for cleaning....
 dims the lights.

A more technical approach

(Two sidenotes on generality, for advanced readers: This discussion will disregard nonlinearity
Nonlinearity

In mathematics, a nonlinear system is a system which is not linear system, that is, a system which does not satisfy the superposition principle, or whose output is not proportional to its input....
. It will also use simple resistance
Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
s, but they can be readily generalized to impedances for AC analysis.)

When discussing the effect of load on a circuit, it is helpful to disregard the circuit's actual design and consider only the Thévenin equivalent. (The Norton equivalent
Norton's theorem

Norton's theorem for electrical networks states that any collection of voltage sources, current sources, and resistors with two terminals is electrically equivalent to an ideal current source, I, in parallel with a single resistor, R....
 works just as well, but this discussion will use the Thévenin form.) The Thévenin equivalent of a circuit looks like this:

Electric Load0
With no load (open-circuited terminals), all of falls across the output; the output voltage is . However, the circuit will behave differently if a load is added. We would like to ignore the details of the load circuit, as we did for the power supply, and represent it as simply as possible. If we use an input resistance
Input impedance

The input Electrical_impedance, Electrical load impedance, or external impedance of a electrical network or electronic device is the Th?venin's theorem electrical impedance looking into its input....
 to represent the load, the complete circuit looks like this:

Electric Load1
Whereas the voltage source by itself was an open circuit
Open circuit

The term Open circuit may refer to:*Open-circuit voltage, the difference of electrical potential between two terminals of a device when there is no external load connected...
, adding the load makes a closed circuit and allows current to flow. This current places a voltage drop across , so the voltage at the output terminal is no longer . The output voltage can be determined by the voltage division
Voltage divider rule

In electronics, a voltage divider is a simple linear circuit that produces an output voltage that is a fraction of its input voltage . Voltage division refers to the partitioning of a voltage among the components of the divider....
 rule:

See also

  • Dummy load
    Dummy load

    A dummy load is a device used to simulate an electrical load, usually for testing purposes....