19.1 CONDUCTION OF ELECTRICITY
19.1.1 Electric Current
1. Meaning of electric current
According to the classical model, freely moving charge carriers found inside a conducting medium (which may be a solid, liquid or gas) exist as tiny particles. They can be forced to move en masse in some specific direction. The flow of charge carriers in a conducting medium is known as an electric current.
2. Types of charge carriers in electric current
The charge carriers that constitute an electric current may be:
- electrons
- positive and negative ions
- holes
One or more kinds of charge carriers could be found moving in a conducting medium.
3. Example of charge carriers moving in different conducting substances
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| Figure 19.1 A series circuit showing conduction through a solid, liquid, and gas using a wire, voltameter, and fluorescent tube connected to a dc supply. |
(a) A dc voltage supply is connected to a series combination consisting of a wire, a voltameter (an electrolyte with two electrodes in it), and a fluorescent tube, as shown in Figure 19.1. There are three kinds of conducting substances in the circuit: a solid (the wire), a liquid (the electrolyte in the voltameter) and a gas (the gas inside the fluorescent tube).
(b) The voltage provided by the dc supply will force the charge carriers to flow in each conducting substance, hence producing an electric current in the whole circuit.
(c) Types of charge carriers in various substances:
| Substances | Charge Carriers |
|---|---|
| Wire | Electrons |
| Electrolyte in voltameter | Positive and negative ions |
| Gas in fluorescent tube | Electrons and positive ions |
19.1.2 Average Current
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| Figure 19.2 Continuous flow of charge carriers through a conductor showing how electric current is produced. |
1. Definition of average current
Consider charge carriers moving continuously through the cross section of a conductor, as shown in Figure 19.2. Since there are charge carriers flowing in the conductor, it means that there is an electric current in the conductor.
The magnitude of the average current is defined as follows:
Let the amount of charge that has flowed through the cross section in time interval Δt be ΔQ coulomb. Then the average current I flowing in the conductor is defined as:
$\boxed{I = \frac{\Delta Q}{Δt}}$
2. Unit of current
The unit of electric current is C s⁻¹ or ampere (A).
19.1.3 Instantaneous Current
If the current in the circuit fluctuates with time, then we may have to use instantaneous current. It is the current that flows at any instant. Its magnitude varies from one instant to another.
For example, at time t = 3.0 s, we may have I = 2.3 A, whereas a short while later, at t = 3.1 s, the current may have become I = 2.8 A.
The expression for instantaneous current is:
$\boxed{I = \frac{dQ}{dt}}$
where charge Q is a function of time t.
Applications of Conduction of Electricity
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Electrical Power Transmission
Electric current is used to transmit electrical energy from power plants to homes, industries, and commercial buildings efficiently.
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Electronic Devices
All electronic devices such as computers, smartphones, and televisions rely on the flow of electric current to operate.
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Circuit Design and Analysis
Understanding average and instantaneous current is essential in designing and analyzing electrical circuits, especially in AC and DC systems.
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Heating Applications
Electric current produces heat (Joule heating), which is used in devices like electric heaters, irons, and kettles.
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Battery and Charging Systems
Electric current is involved in charging and discharging batteries in devices such as phones, laptops, and electric vehicles.
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Industrial Applications
Used in electroplating, electrolysis, and other industrial processes that depend on the flow of electric current.
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Signal Processing and Communication
Instantaneous current is important in signal transmission, especially in communication systems like radio, television, and the internet.
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Measurement and Instrumentation
Devices such as ammeters and sensors use electric current to measure and monitor electrical systems.
Conclusion
Conduction of electricity is a fundamental concept that explains how electric charge flows through different materials such as solids, liquids, and gases. This flow of charge, known as electric current, plays a crucial role in the operation of electrical and electronic systems.
Understanding electric current, including average current and instantaneous current, helps in analyzing how charges move over time and how electrical energy is transferred in circuits. These concepts are essential for both direct current (DC) and alternating current (AC) systems.
In practical applications, the conduction of electricity is vital in power distribution, electronic devices, communication systems, and industrial processes. A clear understanding of this topic provides a strong foundation for studying more advanced concepts in physics and electrical engineering.
Frequently Asked Questions (FAQ) – Conduction of Electricity
1. What is conduction of electricity?
Conduction of electricity is the process by which electric charge flows through a material due to the movement of charge carriers such as electrons or ions.
2. What is electric current?
Electric current is the rate of flow of electric charge through a conductor, usually measured in amperes (A).
3. What is the difference between average current and instantaneous current?
Average current is the total charge flowing per unit time over a period, while instantaneous current is the current at a specific moment in time.
4. What are charge carriers?
Charge carriers are particles that carry electric charge, such as electrons in metals and ions in liquids.
5. How does electricity conduct in solids, liquids, and gases?
- In solids: conduction occurs mainly through free electrons
- In liquids: through positive and negative ions (electrolytes)
- In gases: through ionized particles when sufficient energy is provided
6. What is the formula for electric current?
$I = \frac{Q}{t}$
7. What is instantaneous current?
$I = \frac{dQ}{dt}$
8. What factors affect electrical conduction?
Factors include temperature, material type, electric field strength, and the number of charge carriers.
9. Why is conduction of electricity important?
It is essential for the functioning of electrical devices, power systems, and modern technology.
10. Where is conduction of electricity used in real life?
It is used in power transmission, electronic devices, communication systems, and industrial applications.
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