Otis Singleton
The concept of internal resistance is a fundamental aspect of electrical engineering, and it applies to all kinds of electrical sources. In simple terms, internal resistance refers to the opposition or impedance within an electrical component that hinders the flow of electric charge. This resistance is inherent in the materials used to construct electrical cells, whether they are metals or chemicals. When a power source delivers a current, the internal resistance causes a voltage drop, resulting in a lower measured voltage output than expected. This voltage drop is the product of the current and the resistance. Understanding internal resistance is crucial for analyzing different types of circuits and ensuring efficient energy transfer.
| Characteristics | Values |
|---|---|
| Definition | The internal resistance of an electrical source is the opposition in an electrical component to the movement of electrical charge through it. |
| Formula | The internal resistance of a cell can be calculated using the equation: E = Vtpd + VL |
| Unit | Internal resistance is measured in ohms (Ω). |
| Ideal Current Sources | Ideal current sources have infinite internal resistance. |
| Good Current Sources | Good current sources have very high internal resistance. |
| Practicality | Internal resistance is typically quite low and may only become a problem when the load resistance approaches this value. |
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What You'll Learn
- The concept of internal resistance applies to all electrical sources
- Energy consumption differs between original and equivalent voltage sources
- Internal resistance is typically low and may only become a problem when load resistance is high
- Good real current sources have high internal resistance
- Internal resistance can be calculated using Ohm's Law
The concept of internal resistance applies to all electrical sources
When a power source delivers current, the measured voltage output is lower than the no-load voltage. This difference is the voltage drop caused by the internal resistance. The internal resistance of the power supply results in some of the energy produced being used to push the current through the power supply, and this energy is not available to the external circuit.
Internal resistance is typically quite low and may only become a problem when the load resistance approaches this value. Good constant current sources have high internal resistance, and ideal ones have infinite internal resistance. This means that very little current will flow in good constant current devices, and no current will flow in ideal ones. However, this is not a problem as the resistance is in parallel with the current source, so the higher the resistance, the more current goes through the load when it is connected.
The internal resistance of a cell or power supply can be determined by carrying out an experiment with a series of resistors in series with the cell. For each resistance, the current and Vtpd can be measured, and plotting Vtpd against I will produce a straight-line graph with a negative slope. The emf, internal resistance, and short-circuit voltage can then be determined from the graph.
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Energy consumption differs between original and equivalent voltage sources
All electrical sources have internal resistance. This resistance is due to the materials used in the electrical cell, which can be metal or chemicals. The internal resistance of the power supply results in some of the energy produced being used to push the current through the power supply, which is therefore not available to the external circuit. This is known as the lost volts, and can be calculated using Ohm's Law.
An ideal voltage source has two terminals whose voltage remains constant and does not depend on the amount of current flowing through it. It is also known as an independent voltage source. The internal resistance of an ideal voltage source is zero; it is able to supply or absorb any amount of current.
A practical voltage source, on the other hand, has two terminals whose voltage or potential difference depends on the current flowing through it. It decreases with an increase in the load current. The terminal voltage is less than the actual voltage generated by the source due to internal resistance.
A current source provides a constant current, as long as the load connected to the source terminals has sufficiently low impedance. A practical current source has very high internal resistance, and its current decreases with an increase in voltage or load.
Therefore, the energy consumption differs between original and equivalent voltage sources due to the internal resistance of the power supply, which results in some of the energy being lost as lost volts. The voltage of a practical voltage source decreases with an increase in load current, while the current of a practical current source decreases with an increase in voltage or load.
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Internal resistance is typically low and may only become a problem when load resistance is high
All electrical sources have some internal resistance. This internal resistance is typically low and may only become a problem when the load resistance is high.
Internal resistance in an electrical source refers to the opposition to the flow of electric current within the source itself. It is an inherent property of the source and is primarily due to the materials and components used in its construction. The internal resistance of a source is typically much lower than the resistance of the external load connected to it, which is why it often goes unnoticed.
In most cases, the internal resistance of an electrical source is so low that it can be neglected in circuit analysis. This is especially true for ideal voltage sources, which are commonly assumed to have zero internal resistance. However, in reality, all electrical sources have some finite internal resistance, and in certain cases, this internal resistance can become significant and impact the performance of the circuit.
When the load resistance connected to the electrical source is high, the internal resistance of the source can become a factor. As the load resistance increases, the current flowing through the circuit decreases. If the load resistance becomes comparable to or exceeds the internal resistance of the source, it can no longer be ignored.
In such cases, the voltage supplied to the load may be significantly affected by the internal resistance of the source. The voltage drop across the internal resistance of the source can lead to a lower voltage being delivered to the load, potentially impacting the performance of the circuit or device. This is particularly critical in applications that require precise voltage levels, such as sensitive electronic equipment or battery-operated devices.
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Good real current sources have high internal resistance
All electrical sources have internal resistance. This is because all materials have some resistance, and electrical sources are made from materials such as metals or chemicals. The internal resistance of the power supply results in some of the energy produced in the power supply being used to push the current through the power supply. This energy is not available to the external circuit.
The concept of internal resistance is useful for analyzing many types of circuits. For example, a battery may be modelled as a voltage source in series with a resistance. These types of models are known as equivalent circuit models.
It is important to note that ideal current sources with infinite internal resistance do not exist in the real world. This is because connecting an ideal current source to an open circuit would create the paradox of running a constant, non-zero current through an element with a defined zero current.
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Internal resistance can be calculated using Ohm's Law
All electrical sources have some internal resistance. This is due to the fact that all materials have some resistance, and electrical cells are made from materials such as metal or chemicals. The internal resistance of a cell is scaled in ohms, and it increases with continuous use.
The formula for internal resistance is:
> r = (E - V) / I
Where:
- R = internal resistance
- E = electromotive force
- V = voltage
- I = current
For example, let's say we have a cell with an electromotive force of 3V and a current of 3 x 10^-3 A. We can calculate the internal resistance as follows:
> r = (3V) / (3 x 10^-3 A) - 995 Ω
> r = 1000 Ω - 995 Ω
> r = 5 Ω
So, the internal resistance of the cell is 5 Ω.
It's important to note that the internal resistance of a power supply results in some energy being used to push the current through the supply, which is not available to the external circuit. This energy loss is known as "lost volts" and can be calculated as the product of the current and the internal resistance.
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Frequently asked questions
Internal resistance is the opposition in an electrical component to the movement of electrical charge through it. It is measured in ohms.
Yes, all electrical sources have some internal resistance. This is because all materials have some resistance, and electrical cells are made from materials such as metal or chemicals.
When a power source delivers current, the measured voltage output is lower than the no-load voltage due to the voltage drop caused by the internal resistance. This results in some of the energy produced by the power supply being used to push the current through the power supply, and this energy is not available to the external circuit.
The internal resistance of a power source can be determined by performing an experiment with a series of resistors in series with the cell. By measuring the current and voltage terminal potential difference (Vtpd) for each resistance, you can plot a graph of Vtpd against I, which will produce a straight line with a negative slope. The internal resistance can then be calculated using the data from this graph.
