Wiktor Wise
Electrical circuits are made up of two types of elements: active and passive. Active elements, such as batteries, generators, and operational amplifiers, supply electrical energy to the circuit. Passive elements, such as resistors, capacitors, and inductors, cannot generate electrical energy on their own but consume it. Electrical sources, which are active elements, can be classified as voltage sources or current sources. Voltage sources, such as batteries, provide a constant voltage that is independent of other circuit elements. Current sources, on the other hand, are less common and provide a current that depends on the voltage or current elsewhere in the circuit. These electrical sources can be further categorized as direct (DC) or alternating (AC) sources. While ideal power sources are assumed to provide infinite voltage and current, real-world sources have limitations and are affected by factors such as load and resistance.
| Characteristics | Values |
|---|---|
| Definition | A source is a device that delivers energy into a system. |
| Types | Voltage source, current source, active element, passive element |
| Active element | Supplies continuous energy to a circuit, e.g. batteries, generators, amplifiers |
| Passive element | Physical elements that consume energy but do not generate it, e.g. resistors, capacitors, inductors |
| Voltage source | Provides a constant voltage independent of other circuit elements |
| Current source | Less common than voltage sources; provides a voltage that depends on the voltage or current elsewhere in the circuit |
| Voltage sources in real or practical sources | There is always a resistance connected in series |
| Current sources in real or practical sources | There is always a resistance connected in parallel |
| Direct (DC) or alternating (AC) source | DC source provides constant voltage, AC source varies sinusoidally with time |
| Examples | Generators, photovoltaic cells, thermopiles, batteries |
| Energy conversion | Can convert non-electrical energy into electrical energy and vice versa |
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What You'll Learn
Voltage sources and current sources
A source in an electrical circuit refers to a device that supplies electrical power to a circuit. There are two types of electrical sources: voltage sources and current sources. Voltage sources are active elements that provide a constant voltage that is independent of any other circuit elements. Examples of voltage sources include batteries and generators, which provide a potential difference (voltage) between two points within an electrical circuit, allowing current to flow. The rated voltage across the terminals of a voltage source decreases as the load current it supplies increases.
Voltage sources can be further classified as independent (ideal) or dependent (controlled). An independent voltage source can deliver an infinite amount of energy without loss and its voltage can be specified independently of any other variable in the circuit. On the other hand, a dependent voltage source provides a voltage supply that depends on the voltage across or current flowing through another circuit element.
Current sources, on the other hand, are less common in circuits but complement voltage sources. A current source delivers or absorbs an electric current that is independent of the voltage across it. It provides a constant current as long as the load connected to its terminals has sufficiently low impedance. An ideal current source would provide infinite energy and voltage as the load resistance approaches infinity (an open circuit).
Similar to voltage sources, current sources can be independent or dependent. An independent current source delivers a constant current, while a dependent current source delivers a current proportional to another voltage or current in the circuit. Current sources are implemented using active electronic components such as transistors, which adjust their resistance to compensate for current variations and maintain a constant total resistance in the circuit.
In summary, voltage sources and current sources are two types of electrical sources in a circuit. Voltage sources provide a constant voltage, while current sources deliver or absorb a constant current. Both types of sources can be independent or dependent, and they play a crucial role in supplying electrical power and maintaining stable circuit operations.
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Active and passive elements
A source in an electrical circuit is a device that delivers energy to a system. Sources generate power by converting chemical or mechanical energy into electricity. Examples of electrical sources include generators, photovoltaic cells, thermopiles, and batteries.
Electrical circuits can be divided into two main categories: active elements and passive elements.
Active Elements
Active elements are those that supply energy to an electric circuit and control the flow of charge. They can amplify and control energy. Examples of active elements include:
- Voltage sources
- Current sources
- Diodes
- Transistors
- Generators
- Alternators
- Semiconductor devices
Active elements can be further divided into voltage-controlled and current-controlled sources. Voltage-controlled devices, such as bipolar junction transistors, produce their output current based on the input voltage. Current-controlled active devices, on the other hand, work by restraining another current based on the input current.
Passive Elements
Passive elements, on the other hand, can only receive energy and either dissipate or store it. They do not require any external voltage to function and do not provide gain or amplification. Examples of passive elements include:
- Resistors
- Capacitors
- Inductors
- Transformers
While passive elements do not generate their own energy, they can store energy for a limited time and discharge it. For example, capacitors store energy in an electric field, while inductors store energy in a magnetic field.
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Independent and dependent sources
A source in an electrical circuit refers to a device that supplies electrical power to a circuit. Electrical sources can be categorised into two types: voltage sources and current sources. Voltage sources provide a potential difference (voltage) between two points within an electrical circuit, allowing current to flow around it. Current sources, on the other hand, deliver a specified electric current to the circuit.
Both voltage sources and current sources can be further classified into independent (ideal) or dependent (controlled) sources. Independent sources are those whose output voltage or current remains constant and is not influenced by the voltage or current in any other part of the circuit. They are represented by symbols like a circle with a "+" and "-" for voltage or an arrow for current. These sources are considered ideal because they theoretically deliver an infinite amount of energy without loss. Examples of independent sources include batteries, constant current sources, and ideal power supplies.
On the other hand, dependent sources provide an output voltage or current that depends on another voltage or current in the circuit. They are represented by diamond-shaped symbols. Dependent sources are essential for modelling amplifiers, transistors, and operational amplifiers, as they capture the dynamic behaviour of these devices in circuits. A voltage-controlled voltage source (VCVS) is an example of a dependent source, where the output voltage is proportional to a controlling voltage in the circuit.
It is important to note that the distinction between independent and dependent sources is fundamental to understanding the behaviour of electrical circuits. These concepts are crucial in circuit analysis and design, forming the backbone of circuit theory and practical applications.
In summary, independent sources are those that maintain a constant output voltage or current regardless of other circuit elements, while dependent sources rely on other voltages or currents within the circuit to determine their output.
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Power sources and loads
A power source is a device that supplies electrical power to a circuit. Electrical sources can be classified as voltage sources or current sources. Voltage sources, such as batteries or generators, provide a potential difference (voltage) between two points within an electrical circuit, allowing current to flow around it. The rated voltage across the terminals of a voltage source drops as the load current it supplies increases. Current sources, on the other hand, are less common in circuits but complement voltage sources.
Voltage sources can be further classified as independent (ideal) or dependent (controlled). An ideal voltage source can theoretically deliver an infinite amount of energy without loss, whereas a controlled voltage source provides a voltage supply whose magnitude depends on the voltage across or current flowing through another circuit element.
Power sources generate power by converting chemical or mechanical energy into electricity. Examples of power sources include electric generators, batteries, photovoltaic cells, thermopiles, and primary-cell batteries.
A load, on the other hand, is a device that consumes electrical power from a circuit. It extracts energy from the system, resisting the flow of electrical current and creating a voltage drop. Examples of loads include resistors, lamps, and electric motors.
In a circuit, the addition of a load changes the behaviour of the circuit, converting electrical energy back into motion, light, heat, or sound. For example, when a CD player is connected to an amplifier, the CD player is the source, and the amplifier is the load.
Understanding the distinction between sources and loads is essential for troubleshooting and analysing electrical circuits, especially in industrial applications.
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Primary and secondary energy
Primary energy sources are the natural, unconverted forms of energy found in nature, also known as unconverted or original fuels. They are the initial sources of energy that undergo extraction or harvesting before they can be used to generate electricity, perform mechanical work, or provide heat. Examples of primary energy sources include fossil fuels such as coal, oil, and natural gas, which are extracted from the Earth's crust and burned to release heat energy. Other primary energy sources include renewable resources such as solar energy, wind power, hydropower, and biomass, which are harnessed directly from nature and can be converted into electricity without causing significant environmental damage. Nuclear fuel, powered by uranium and plutonium, is another example of a primary energy source that is zero-emission due to its lack of carbon dioxide emissions, although it can cause environmental damage through mining activities.
Secondary energy, on the other hand, is energy that has already been converted from primary sources. It is the energy that results from the conversion of primary energy sources into a transportable form. For example, when coal is burned in a power plant to produce electricity, the electricity generated is a form of secondary energy. Other examples of secondary energy include liquid fuels such as gasoline and diesel, which are refined oil products, as well as heat. Secondary energy cannot be harnessed directly from nature but is generated from primary fuels.
The choice between primary and secondary energy sources has important implications. For instance, in an experiment studying electricity generation efficiency, using primary energy data (e.g., the energy content of coal) would provide insights into the inherent losses and efficiency of the conversion process. In contrast, relying on secondary energy data (e.g., the electricity generated from coal) may overlook the losses associated with energy conversion.
Additionally, the conversion of primary to secondary energy can be inefficient, especially in the case of fossil fuels, which have particularly large primary energy losses. Transitioning away from fossil fuels and towards renewable sources can help reduce these losses and improve sustainability.
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Frequently asked questions
A source in an electrical circuit is a device that supplies electrical power to the circuit. Sources can be classified as voltage sources or current sources. Voltage sources, such as batteries, provide a constant and specified voltage, while current sources are less common and depend on the voltage elsewhere in the circuit.
A source delivers energy into a system, while a load extracts energy from a system. Examples of sources include generators, batteries, and photovoltaic cells, which create electrical voltage to motivate current flow. Loads, such as resistors and lamps, resist the flow of electrical current, creating a voltage drop.
Sources in an electrical circuit can include batteries, generators, and photovoltaic cells. Batteries are an example of direct current (DC) sources, while the wall socket in your home is an alternating current (AC) source. Capacitors and rechargeable batteries can also act as sources or loads, depending on the other components in the circuit.
