Beatrice Lang
An electric circuit is a continuous and closed path through which electric current flows. It consists of conducting wires and other resistances (like lamps) between the terminals of a battery, along which an electric current flows. For the flow of electricity, the entire circuit must be made up of conductors. An electric circuit with no current flowing through it is known as an open circuit.
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What You'll Learn
Open and closed circuits
An electric circuit is a continuous and closed path through which electric current flows. It contains components like a cell or battery, plug key, wires, and electric components like an ammeter or voltmeter. A voltmeter is used to measure the potential difference or voltage in a circuit.
Now, an open circuit is where the energy is not flowing through it. It is not complete, and electricity will not flow from the active energy source to the required endpoint as the path is open or not closed. This could be due to a manual disconnection, a blown fuse, missing components, or faulty wiring. There is no potential difference with an open circuit.
A closed circuit, on the other hand, is where the energy is allowed to flow through it by turning it on. Electricity flows from the energy source to the desired endpoint. A closed circuit will have a potential difference. It is important to note that a circuit with a dead battery can still be a closed circuit, but it cannot do any work.
To summarise, the key difference between open and closed circuits is the flow of energy. In an open circuit, there is no flow of energy due to an incomplete path, while in a closed circuit, energy flows through the continuous and closed path.
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Electric current
Electrons are negatively charged particles, so when they move, a number of charges moves, and we call this movement of electrons electric current. The number of electrons that are able to move governs the ability of a substance to conduct electricity. Some materials allow the current to move better than others. Based on this ability to conduct electricity, materials are classified into conductors and insulators. Conductors allow for the free flow of electrons from one particle to another, enabling charge transfer through the free movement of electrons. Insulators, on the other hand, impede the flow of electrons. Silver and copper are good conductors, while rubber and glass are very good insulators.
The flow of electric current requires certain prerequisites to be in place. The circuit must include an energy source, such as a battery, that produces voltage. Voltage is essential to direct the flow of electrons in a single direction. Without voltage, electrons move randomly and undirected, and current cannot flow. The circuit forms a closed conducting loop, and it is said to be closed or complete when a switch is turned on. The force that acts on the electrons to make them move in a certain direction is known as electromotive force, and its quantity, or pressure, is known as voltage, measured in volts.
The electric current is denoted by the letter 'I' and is expressed by the rate of flow of electric charges. This rate of flow refers to the amount of charge flowing through a particular area in unit time. The small quantity of electric current is expressed in milliampere (written as mA) and microampere (written as pA).
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Potential difference
An electric circuit is a continuous and closed path through which an electric current flows.
Now, onto potential difference:
The potential difference is equal to the amount of current multiplied by the resistance. It can also be described as the work done in moving a unit positive charge from one point to another. When W joules of work is done in bringing a test charge Q coulombs from infinity to point P, the electric potential V at point P is V=W/Q.
The potential difference between two points in a circuit is similar to the difference in water pressure that enables the flow of water.
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Electric fuses
An electric circuit is a continuous and closed path through which electric current flows. Electric fuses are an essential component of any electric circuit or electronic system. They are safety devices that protect electrical equipment from excessive current and prevent short circuits or mismatched loads. Fuses are designed to break the circuit and stop the current flow in the event of a fault or overload.
Fuses are typically made of a metal wire or strip with a high resistivity and low melting point. When an excessive amount of current passes through the fuse, the heating effect of the current causes the wire to melt, interrupting the circuit and stopping the flow of charges. This is why fuses are often referred to as sacrificial devices—they are designed to fail and break the circuit, protecting the rest of the system.
The thickness of a fuse wire is determined by the amount of current flowing through the circuit. The wire is chosen to withstand the normal current but melt when exposed to an excessive amount. This intentional weak point in the circuit prevents damage to other components and helps prevent safety hazards to humans.
Fuses come in different types, including high-voltage and low-voltage varieties. High-voltage fuses include thermal fuses, which protect equipment from overheating, and cartridge-type fuses, which prevent corona effects at high voltages. Low-voltage fuses can be rewirable or cartridge-type. Rewirable fuses are commonly used in house wiring, while cartridge fuses are sealed in containers with metal contacts at both ends.
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Conductors and resistors
An electric circuit is a continuous and closed path that transmits electric current to electronic devices. Conductors are substances that allow electricity to flow through them. A conductor can be defined as a substance that offers less opposition to the flow of current. Some examples of conductors include copper, iron, and steel. The resistance of a conductor depends on its temperature and strain. For instance, by placing a conductor under tension, its length increases, and its cross-sectional area decreases, resulting in increased resistance. On the other hand, conductors under compression experience a decrease in resistance.
Resistors are a type of conductor made from a wide range of materials, including semiconductors. The choice of material depends on factors such as the desired resistance, energy dissipation requirements, precision, and cost. Resistors are used to control the flow of current in a circuit. The resistance of a resistor is influenced by its geometry and the material it is made of. For example, a long, thin copper wire has higher resistance than a short, thick wire of the same material.
The relationship between voltage, current, and resistance is described by Ohm's Law. According to this law, the current through a conductor is directly proportional to the voltage across it. In other words, the voltage drop or difference provides the driving force that pushes current through a resistor. This relationship can be compared to water flowing through a pipe, where the voltage drop is analogous to the pressure drop that pushes water through the pipe.
Photoresistors, or light-dependent resistors, are a type of resistor commonly used as light detectors. They are made from semiconductors and exhibit photoconductivity, meaning their resistance changes when exposed to light.
In summary, conductors are substances that facilitate the flow of electric current, with their resistance influenced by temperature and strain. Resistors are a specific type of conductor used in circuits to control the flow of current, and their resistance is determined by factors such as geometry and the type of material used. Ohm's Law describes the relationship between voltage, current, and resistance in these conductors and resistors.
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Frequently asked questions
An electric circuit is a continuous and closed path through which electric current flows. It consists of conducting wires and other resistances (like lamps) between the terminals of a battery, along which an electric current flows.
An electric circuit through which no electric current flows is known as an open circuit. This can occur if the plug is removed or the connecting wire breaks. A closed circuit is one through which electric current flows continuously.
The unit of current is Ampere, or Amps. 1 Ampere is 1 coulomb of charge flowing through any cross-section of a conductor in 1 second.
